Workshop on assembling of superstructures in soft matter BOOK OF

Workshop on assembling of superstructures

in soft matter

BOOK OF ABSTRACTS

October 11-13th 2012, Ljubljana, Slovenia

(i)

Workshop on assembling of

superstructures in soft matter

BOOK OF ABSTRACTS

October 11-13th 2012, Ljubljana, Slovenia

(iii)

Workshop on assembling of superstructures in soft matter is organized by the HIERARCHY network, with a number of prominent invited speakers, to wrap up the conclusions of our 4-year European research network and to discuss perspectives for further evolution of this field. The research in HIERARCHY network is aimed at complex soft matter structures that brought together research groups from UK, Germany, Netherlands, and Slovenia. Building on experiments, modeling, and applications it bridges the gaps between, physics, chemistry, biology, material science, and technology, which will give the broad perspective also to this workshop. Scientific Board

Roeland Nolte (Radboud University Nijmegen, Netherlands) Theo Rasing (Radboud University Nijmegen, Netherlands) Alan Rowan (Radboud University Nijmegen, Netherlands) Igor Muševič (Jožef Stefan Institute, Slovenia) Martin Möller(RWTH Aachen, Germany) Cees Bastiaansen (TU Eindhoven, Netherlands) Slobodan Žumer (University of Ljubljana, Slovenia) Stephan Herminghaus (MPI Dynamics & Self-Organization – Göttingen, Germany) Dick Broer (Philips – Eindhoven, Netherlands) Janez Pirš (Balder – Ljubljana, Slovenia) Jules Beekwilder (Plant Research International – Wageningen, Netherlands) Owain Parri (Merck UK – Southampton, UK)

Local Organizing Committee

Igor Muševič, chair Slobodan Žumer, co-chair Matjaž Humar Miha Ravnik Jožef Stefan Institute, University of Ljubljana and CO NAMASTE

Editors

Matjaž Humar Miha Ravnik

Financial support

European Commission, FP7, PEOPLE, MARIE CURIE ACTIONS, Marie-Curie Initial Training Networks

(v)

Conference Venue The workshop will be held in Cankarjev dom (CD) Cultural and Congress Centre. CD is located in the centre of Ljubljana, at a walking distance from several hotels and the attractive Old Town. More precisely, the conference venue is in the Klub CD which is the conference hall at the roof-top of the CD Centre (5th floor). The CD centre has several entrances. The conference hall is easiest accessed by entering the entrance from Erjavčeva cesta street (see the map below). On the entrance it is written Klub CD. Once entering the CD take the elevator on the right which will be marked with the conference board.

Address: Cankarjev dom, Prešernova cesta 10, Ljubljana Phone: + 386 (0)1 2417 122 Email: [email protected] Website: www.cd-cc.si/congress Conference Dinner The dinner on Thursday, October 11th will be held in a traditional Slovenian restaurant Šestica. The restaurant is located on Slovenska cesta near the city centre (see the map below). Address: Gostilna Šestica, Slovenska cesta 40, Ljubljana Website: www.sestica.si

(vii)

Program

Thursday - October 11th 8:00-8.55 Registration 8:55-9:00 Welcome 9:00-9:40 Ivan I. Smalyukh: Optical nanolabs in liquid crystal defects (invited) 9:40-10:00 Sergey Semin: Bio-nano-photonics: highly brilliant two-photon probes

and waveguiding from self-assembled peptide tubes 10:00-10:20 Tine Porenta: Complex field-stabilised nematic defect structures in

Laguerre-Gaussian optical tweezers 10.20-10.50 Coffee break 10:50-11:30 Etienne Brasselet: Topological defects: interplay between light and liquid

crystals (invited) 11:30-11:50 Venkata Subba Rao Jampani: Chiral nematic colloidal structures, pair

interactions, 3D organization and photonic applications of nematic colloids 11:50-12:10 Anupam Sengupta: Liquid crystal microfluidics: surface, elastic and viscous

interactions on a microfluidic platform 12.10-14.30 Lunch 14:30-15:10 Moonsoo Park: Liquid Crystal Optical Films for 3D-Display (invited) 15:10-15:30 Amir Asgharsharghi: ISO Standard for LCD light shutters for Eye

Protection applications 15:30-15:50 Laura Cattaneo: Fast and energy efficient liquid crystal switches using

patterned command layer 15.50-16.20 Coffee break 16:20-17:00 Liang-Chy Chien: Synergistic effects of dispersion of polypeptides in Blue

Phase Matrixes (invited) 17:00-17:20 Firat Ozdemir: Spontaneous Formation of Polymeric Onions 17:20-17:40 Heng Zhang: Nano-channel formation by wedge-shaped sulfonates and

their ion-conductivity study 19:00 Conference dinner

(viii)

(ix)

Friday – October 12th 9:00-9:40 Tommaso Bellini: Exploring Soft Matter with DNA (invited) 9:40-10:00 Fuat Topuz: DNA Nanogels as Cancerogens Scavengers 10:00-10:20 Anke Kristin Trilling: Oriented detection elements in biosensors: site-

specific functionalized llama antibody fragments 10.20-10.50 Coffee break 10:50-11:30 Mark R. Wilson: Self-assembly of liquid crystalline nanostructures in aqueous

solution (invited) 11:30-11:50 Alexandra Alvarez Fernandez: Ionic liquid crystals: towards addressable

water 11:50-12:10 Karthik Reddy Peddireddy: Solubilization of Thermotropic Liquid Crystal

Compounds in Aqueous Surfactant Solutions 12.10-14.30 Lunch (**13:00 meeting for heads of the network groups**) 14:30-15:10 Arjun G. Yodh: Self-Assembling Temperature-Sensitive Colloids for

Investigation of Melting, Frustration, and Jamming Phenomena (invited) 15:10-15:30 Giorgio Mirri: Stabilisation of ordered colloidal structures and deformed

defects by polymerisation of reactive liquid crystalline matrices 15:30-15:50 Mojca Vilfan: Self-assembled biomimetic cilia 15.50-16.20 Coffee break 16:20-17:00 Helena Godinho: Wrinkling Labyrinth Patterns on Elastomeric Janus

Particles (invited) 17:00-17:20 Owain Parri: Optical and shape anisotropic particles 17:20-17:40 Maryam Nikkhoo: Topological defects and shape-controlled interaction

in nematic liquid crystal 17:40-18:00 Miha Ravnik: Tilings of nematic colloidal platelets 18:00-19:00 Poster session

(xi)

Saturday - October 13th 9:00-9:40 Jun-ichi Fukuda: Cholesteric blue phases under confinement and electric

field (invited) 9:40-10:00 Yuji Sasaki: High-resolution calorimetric studies on liquid crystal

transitions in thin layers 10:00-10:20 Wei-Ta Wu: Controlling the Pretilt Angle of Nematic Liquid Crystals by

Obliquely Sputtering Iron Oxide 10:20-10:40 Xunda Feng: Surface induced ordering phenomena at liquid crystal

interfaces laden with surface active molecules 10:40-11:10 Coffee break 11:10-11:50 Teresa Lopez-Leon: Liquid Crystalline Superatoms (invited) 11:50-12:10 Andriy Nych: Assembly and Control of 3D Nematic Colloidal Crystals 12:10-12:30 Anna Ryzhkova: Nanocolloids interactions in nematic liquid crystal 12:30-12:40 Closing remarks

OORRAALL PPRREESSEENNTTAATTIIOONNSS

1

Optical nanolabs in liquid crystal defects

Ivan I. Smalyukh1,2

1Department of Physics, Materials Science and Engineering Program, Department of Electrical, Computer, and Energy Engineering, and Liquid Crystals Materials Research

Center, University of Colorado at Boulder, Boulder, Colorado 80309, United States 2Renewable and Sustainable Energy Institute, National Renewable Energy Laboratory

and University of Colorado at Boulder, Boulder, Colorado 80309, United States E-mail: [email protected]

Plasmonic metal nanoparticles are of great interest for applications in

nanophotonics, third-generation solar cells, photothermal therapies, and imaging. Nonspherical metal particles can exhibit surface plasmon resonance (SPR) tunable throughout the visible and near-infrared spectral regions, and their plasmonic properties can be further enhanced by the collective behavior when the inter-particle separation becomes comparable to their size. For example, multipole SPRs and well-defined assemblies of nanoparticles give simple ways of obtaining a non-trivial magnetic response and making plasmonic colloidal systems potentially useful for the fabrication of optical metamaterials. Near-field proximity of plasmonic nanoparticles can also alter the fluorescent behavior of semiconductor quantum nanoparticles and molecular dyes. Although notoriously difficult to achieve, precise arrangement of metal nanoparticles can yield highly desirable functionality for applications such as nanoantennas. Non-contact manipulation and trapping techniques that would allow for precise nanoscale positioning and alignment of anisotropic metal, semiconductor, and other particles with respect to each other in tunable fluid host media are in a great demand. This lecture will demonstrate scaffolding of plasmonic and semiconductor nanoparticles by topological defects stabilized by colloids and inherent chirality in liquid crystal host media [1-3]. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles not only stably localize in defects, but also align with respect to each other and with respect to the far-field liquid crystal director. Using laser tweezers, we manipulate the ensuing colloidal dimers and superstructures, probing the strength of elastic binding and demonstrating hierarchical self-assembly [1]. Oriented localization in topological point and line defects in liquid crystals enables creation of a “nanoscale laboratory” in a fluid host medium to study the interplay of properties of small numbers of metal and semiconductor nanoparticles. The lecture will conclude with a discussion of applications of our findings in many-body experiments that probe photonic effects due to nanoscale interactions of individual and small groups of colloids such as complex-shaped plasmonic metal nanoparticles and quantum dots and rods. 1. B. Senyuk, J. S. Evans, P. Ackerman, T. Lee, P. Manna, L. Vigderman, E.R. Zubarev,

J. van de Lagemaat, and I.I. Smalyukh, Nano Lett 12, 527-1114 (2012). 2. J. S. Evans, P.J. Ackerman, D. J. Broer, J. van de Lagemaat, and I. I. Smalyukh,

(2012). 3. B. Senyuk and I.I. Smalyukh, Soft Matter 8, 8729 - 8734 (2012).

3

Bio-nano-photonics: highly brilliant two-photon probes and waveguidingfrom self-assembled peptide tubes

S. Semin, J. Deurloo, A.van Etteger, and Th.Rasing

Radboud University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525AJ Nijmegen, The Netherlands

Diphenylalanine peptide is one of the simplest building-blocks which self-assembles innano- and micro structures driven by intermolecular forces. Microtubes based on thismaterial (FF-PTs) belong to a unique class of self-assembled biomaterials with a widerange of interesting properties including biocompatibility, mechanical rigidity, ferroelec-tricity and chemical stability. In addition they do not show environmental or cytotoxicthreats.FF-PT samples were prepared by a self assembly process from peptides dimers. Thedimer was dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol up to concentration 100 mg/ml.The stock solution was further diluted in deionized water to a concentration of 0.2-0.5mg/ml[1]. The typical diameter of the peptide structures varies from hundreds of nanome-tres to tens of micrometres. The length of the tubes can reach several microns.Second harmonic generation and two-photon luminescence results related with the tubescrystal structure are reported. These techniques reveal a phase transition which occurs inthe FF-PT by laser or heat treatment. Evidence of the phase transition was also shownby XRD and PFM (AFM in piezo mode)[2]. The possibility to control the local opticalproperties of individual FF-PTs by a laser was shown. The observed waveguiding effectoffers new applications in photonics.

[1] Amdursky, N., Beker, P., Koren, I., Bank-Srour, B., Mishina, E., Semin, S., Rasing,T., et al. (2011). Structural transition in peptide nanotubes. Biomacromolecules, 12(4),134954.[2] Heredia, A., Bdikin, I., Kopyl, S., Mishina, E., Semin, S., Sigov, a, German, K., etal. (2010). Temperature-driven phase transformation in self-assembled diphenylalaninepeptide nanotubes. Journal of Physics D: Applied Physics, 43(46), 462001.

4

Complex field-stabilised nematic defect structures in Laguerre-Gaussianoptical tweezers

Tine Porenta1, Miha Ravnik1,2, and Slobodan Zumer1,2,3

1 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000Ljubljana, Slovenia

2 Center of Excellence NAMASTE, Jamova 39, 1000 Ljubljana, Slovenia3 Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Complex optical beams can produce highly non-uniform electric field profiles on microm-eter and sub-micrometer scale that can be used for the formation of complex nematicstructures [1]. We demonstrate the formation of various complex nematic structures us-ing Laguerre-Gaussian beams. The optical beam polarization winding number directlyimprint into the profile of the nematic director, producing complex symmetric arrange-ments of nematic defect loops inside optical beam which number is exactly equal topolarization winding number[2]. The role of the absorption is addressed, demonstratingcomplex local heating and ’softening’ of the nematic within the optical beams. Tuningof the demonstrated field-stabilised structures is studied by increasing the intensity orabsorption of optical beam. Generally by increasing either beam intensity or absorptionin nematic, the region of an effective coupling between the nematic and optical electricfield increases. Consequently, the defect loops and the structure as a whole expand. Toconclude, using modelling to find stable defect structures based on the delicate balanceof the effects due to chirality, confinement, surface anchoring profiles, external fields, andpresence of colloidal particles may lead to use in various fields of photonics, optics, andcomplex material design.

[1] I. I. Smalyukh, Y. Lansac, N. A. Clark and R. P. Trivedi, Nat. Mater.,Three-dimensional structure and multistable optical switching of Triple Twist Toron quasiparti-cles in anisotropic fluids, 9, 139 (2010)[2] T. Porenta, M. Ravnik and S. Zumer, Complex field-stabilised nematic defect structuresin Laguerre-Gaussian optical tweezers, Soft Matter, 6, 1865 (2011)

5

Topological defects : interplay between light and liquid crystals

E. Brasselet

‘Singular Optics & Liquid Crystals’ group Laboratoire Ondes et Matière d’Aquitaine, CNRS, Université Bordeaux 1

351 cours de la Libération, 33405 Talence, France E-mail : [email protected]

Abstract

Liquid crystals are well-known to exhibit a wealth of topological defects structures. Optical fields as well, this is the object of study of a research field called singular optics. Here I will discuss how light interact with material defects and vice-versa. What make the interplay between light and liquid crystals unique are the self-assembling capabilities and the high sensitivity to external fields of soft matter. In particular, this includes the controlled generation of optical singularities using liquid crystals topological defects that might be useful for singular photonics applications. Inversely, light can induce liquid crystals topological defects via singular optical nonlinear orientational processes such as singular cross-phase optical modulation, singular self-phase optical modulation, and nonlinear optical vortex precession.

6

mailto:[email protected]�

Chiral nematic colloidal structures, pair interactions, 3D organization and

photonic applications

V.S.R.Jampani1,*, M. Škarabot1, 2, M. Humar1, M. Ravnik2, S. Čopar2, S. Žumer1, 2 and I. Muševič1, 2

1Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 2University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia

We explored the topology and geometry of closed defect loops in chiral nematic colloids. Laser tweezers-assisted quenching of the local nematic order was used to discern the defect line propagation in chiral nematic colloids [1]. We show experimentally how -1/2 defect loops wrap around single colloidal particle in π, 2π and 3π twist in a cholesteric cell. The entangled structures of pairs of colloids in π cell have resulted in a rich number of structures compared to planar nematic and twisted π/2 cells [2]. At least 25 different entangled structures with pairs of colloids were observed in π cell. We also study pair interactions and 3D self-assembly of colloidal structures. The pair interaction potential was calculated from the measurements of forces between colloidal particles [3]. The observed pair potential landscapes are attractive, but are not monotonic functions of colloidal separation. The observed local minima lead to metastable states in colloidal pair interactions. The number of observed metastable states increases with increasing chirality of the cell. In addition to this, partially ordered and most probably entangled 3D structures were observed in chiral nematic colloids with a larger number of particles. Furthermore we have studied resonant transfer of light into the nematic droplets from the planar waveguides. The prism film coupler setup was used to couple supercontinuum source to the planar waveguide. The modes in the waveguide were coupled to whispering gallery modes (WGMs) in the nematic LC droplet close to the waveguide. WGMs are characterized by the total internal reflection at the periphery of the droplet and can be seen as equally spaced resonances [4].

Figure 1. (a)-(d) colloidal dimer and cluster in π cell, (f)-(h) Laser tweezers stretched Defect lines, (i) Two layers of 3D entangled colloidal structures in a chiral nematic cell. (j) Whispering gallery modes from the LC microcavity on waveguide. References: [1] V. S. R. Jampani et al., Colloidal entanglement in highly twisted chiral nematic colloids: Twisted loops, Hopf links and trefoil knots, Phys. Rev. E 84, 031703 (2011). [2] U. Tkalec et al., Reconfigurable knots and links in chiral nematic colloids, Science 333, 62 (2011). [3] I. Muševič, et al., Two- dimensional nematic colloidal crystals self assembled by topological defects, Science 313,954 (2006). [4] M. Humar, et al., Electrically tunable liquid crystal optical microresonators, Nat.Photonics 3, 595 (2009). _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ * presenting author; E-mail: [email protected]

7

Liquid crystal microfluidics:

surface, elastic and viscous interactions on a microfluidic platform

Anupam Sengupta

Max Planck Institute for Dynamics and Self Organization, Dynamics of Complex Fluids,

Am Faßberg 17, Göttingen-37077, Germany

Flow of anisotropic fluids (e.g. liquid crystals) is inherently complex due to coupling

between the flow and the long-range order. Experiments carried out at micro scales further

reveal the influence of surface properties on the static and dynamic outcomes. We use

microfluidic platforms to tune one or more of the above competing components, and explore

the resulting equilibrium states. The delicate but intricate balance between the viscous,

elastic and surface forces was consequently used to devise optofluidic and micro-scale-

transport applications. On one hand the novel applications complement the conventional

microfluidic capabilities, and on the other, broaden the reach of isotropic microfluidics by

offering competitive advantages. Standard microfluidic techniques and a combination of

polarizing optical microscopy, fluorescence confocal polarizing microscopy and particle

tracking methods were emloyed for the investigations.

8

Liquid Crystal Optical Films for 3D-Display

Moonsoo Park Merck Chemicals Ltd., Chilworth Technical Centre, University

Parkway, Southampton SO16 7QD, UK

Three-dimensional display (“3D-display”) is very interesting technology which provides exciting visual experience, and makes the new concept of product development and market creation possible.

The mega hit of Avartar in 2009 revived public interests in 3D displays, triggering its rapid growth. Especially, the portion of 3D TV is expected to be 20% of the total TV market in 2014. Current 3D TV technology can be realized by using special glasses and optical film which control the polarization and the path of the light.

In this presentation, we would like to discuss the Film Patterned Retarder(FPRTM) technology and our own photo alignment material used in the polarization type stereoscopic 3D-displays.

9

ISO Standard for LCD light shutters for Eye Protection applications

A. Asgharsharghi, B. Urankar, D. Ponikvar, J. Turk and J.Pirs

Jožef Stefan Institute, Ljubljana, Slovenia

Active Liquid Crystal light shutters are gaining increasing importance in the field of “eye protection” against fast intense light flashes that are typically encountered in welding or various medical applications (e.g. intense pulse light skin treatment,..). They are potentially very interesting also for reducing glare with car drivers (sun, night driving,…) and airplane pilots.

The fact is that fast changes of light represent considerate stress for human eyes. Present safety standards are predominantly focused on permanent eye damage (e.g. lasers,…). Specific temporary hazards not causing permanent damage are not adequately specified yet, though they are causing temporary blindness, reduced color/pattern recognition, eye fatigue,…. and hence reduced comfort and performance of the user.

A new “safety standard” has been proposed to the expert group ISO/TC94/SC6/WG2 and WG4 of the International Standard Organization. Two new test methods for the most frequent causes of such hazards - angular dependence of the protective shade and inadequate light sensitivity, have been developed. In order to make the implementation of the proposed ISO Standard possible, a new standard plasma light source has been developed. It allows not only for the standardization measurement and “ISO” quality approvals of the protective active glasses but also represents an ideal light source for medical studies of these phenomena, as it can be used under clinical conditions.

The proposal for the new ISO safety standard has been already evaluated world-wide and is in a process of being accepted.

References: 1. Auto-Darkening Welding Filters - State Of-The-Art and Perspectives, Welding in South East Asia, Bangkok Nov. 21-22,

Proceedings, No 44, pp 393-406. (2006) 2. Wide-view STN liquid crystal light shutter”, Appl. Optics, 47, no.12, (2008). 3. Variable Contrast, Wide Viewing Angle LCD Light-Switching Filter" CIP US patent appl.: Pat Appl. No. 13/208,378 4. High contrast, wide-viewing angle LCD light filter”, WO 2006 122679 A1; EP1883854; US 8,026,998 5. Artificial welding and ambient light sources – calibration: COBISS.SI-ID 23568167

10

FAST AND ENERGY EFFICIENT LIQUID CRYSTAL SWITCHES

USING PATTERNED COMMAND LAYER Laura Cattaneo, Paul Kouwer, Alan Rowan, Theo Rasing Radboud University Nijmegen, IMM, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands. Currently, most of the efforts in Liquid Crystal (LC) technology are devoted to realize faster switching since their slow responsivity to external stimuli. Switching speeds of a hybrid-aligned nematic device in the sub-millisecond range have been achieved for cells with patterned self-assembled monolayers (SAMs) on indium-tin-oxide (ITO) substrates [1,2]. To achieve such fast LC responsivity, thermal treatments of the patterned SAM-on-ITO are required, which increase the relative anchoring energy experienced by the interacting LC molecules. Furthermore, to investigate the switching mechanism of such patterned hybrid cells in detail, different confinement conditions have been tested it terms of LC thickness and pattern size, as shown in Figure 1(a-c). We find that a proper engineering of this patterned command layer can be used as a versatile tool, adaptable to different silane type for 2D & 3D LC applications. Preliminary results will be presented.

Figure 1 (a), (b) and (c) show a square pattern cell, consisting out of 44 m2 , 22 m2 and

11 m2 square boxes, viewed in white-light transmission between crossed polarizer and analyzer and the full wave retardation plate. The cells thickness is 4 m.

References:

[1] B. Lee and N.A. Clark, Alignment of Liquid Crystals with Patterned Isotropic Surfaces Science, 291, 2576-2580, (2001).

[2] J. Zhang, M. I. Boamfa, A. E. Rowan, and T. Rasing, Compartmentalized Multistable Liquid Crystal Alignment, Adv. Mater. 22, 961-965, (2010).

11

Synergistic effects of dispersion of polypeptides in Blue Phase Matrixes

Everett Rheinhalt, Jenny Marie Wong, Emine Kemiklioglu, Jeoung-Yeon Hwang and

Liang-Chy Chien

Chemical Physics Interdisciplinary Program and Liquid Crystal Institute Kent State University, Kent, Ohio, USA

Email: [email protected]

Since the first observation of blue colored substance by Reinitzer [1], blue phase liquid crystals (BPLCs) have drawn a great deal of attention recently due to the demonstration of potential applications as information displays. Because the Skyrmion arrangement requires high bend curvature of director to stabilize the blue phase, thermodynamically stable blue phases have been predicted and demonstrated that the planar helix structure generally associates with the cholesteric phase and becomes unstable at the temperature near the transition point. Due to the free-energy cost of disclination, blue phases was usually appeared within few degrees of Celsius between the chiral nematic (or smectic) and isotropic phases [2].

Ravnik, et al. [3] has recently established a proof-of-principle that colloids or nanopartiacles can be used to mediate defects in cubic lattice and potential stabilization of such hetereogeneous systems. But the possible design parameters such as the size and density of nanoparticles to reach wide blue phase temperature range are still evolving. Our work seeks for modulating the surface tension and elastic property of blue phase media that enable a Kerr device with wide operation temperature and at a low switching voltage.

In this presentation, we followed the report in studying a wide range of blue phase nanocomposites with colloids, aerogels and nanotubes that exhibit a wide temperature range blue phase liquid crystals for display applications. Systematically tuning of the elastic constant and dielectric anisotropy values of the blue phase liquid crystal (BPLC) temperature range leads to broadening the BP temperature. We found that as the chiral concentration of the blue phase increases, the BP temperature range decreases. The studied BPLCs also exhibit fast response time and low switching voltage. These results can be explained based on the defect theory and would give effective guidance during the application of BPLC. The BP temperature range of the nanocomposites was validated with theoretical estimation [4].

Intrigued by the helical structures of proteins (consisting of one or more polypeptides) and DNA in living systems, many research works have focused on the helical conformation in self-assembled system. We will introduce a simple analytical platform for sensors based on BPLCs dispersion of various types of peptides. The concept of chirality playing an important role in molecular self-assembly into liquid crystal phase may have the synergistic effect on the host matrix. Similar to the helix-helix transition of macromolecular conformation, we studied the effect of size and shape as well as helical handedness changes with the host matrix that exhibits a blue phase. Detailed materials chemistry and physics, optical and electro-optical study will be presented.

1. Reinitzer, F., Monatsh. Chem., 9, 421-441 (1888). 2. Johnson, P. L., Flack, J. H. and Crooker, P. P., Phys. Rev. Lett., 45, 641-644 (1980). 3. Ravnik, M., Alexander, G. P., Yeomans, J. M., Zumer, S., Faraday Discuss., 144, 159–169 (2010). 4. Meiboom, S. S., J. P.; Amderson, P. W.; Brinkman, W. F., Phys. Rev. Lett. 46, 1216-1219 (1981).

12


Spontaneous Formation of Polymeric Onions Firat Ozdemir, Helmut Keul, Ahmed Mourran, Martin Moeller

DWI an der RWTH Aachen e.V , Forckenbeckstraße 50, D-52056 Aachen Germany

Despite many advantages of the polymersomes against liposomes, they exist exclusively in unilamellar form as the repulsion of large hydrophilic coils of block copolymers prevents the spontaneous formation of multilamellar polymersomes. In this study, our aim was to overcome this limitation by utilizing double comb copolymers instead of block copolymers1.For the synthesis of the amphiphilic double-comb copolymers we followed a “grafting to” approach. First a linear copolymer of glycidol and allyl glycidyl ether was synthesized. Next hydrophilic and hydrophobic side-chains were attached via activated carbonate coupling and thiol-ene addition, respectively. In both cases the conversions were found to be quantitative2

. The resulting polymers were characterized by NMR, GPC and DSC. Subsequently, we investigated the self-assembly behavior of the polymers. By applying different means of hydration we were able to form small (ca. 100 nm) and giant (5-50 µm) multilayer vesicles as well as giant unilamellar vesicles from these polymers. The vesicles were characterized by Dynamic Light Scattering and Differential Interference Contrast Microscopy. In addition, permeability of the membranes to model dye molecules is studied by Fluorescence Microscopy.

1 Discher DE, Ahmed F ,Annu. Rev. Biomed. Eng., 2006. 8:323–41 2 Ozdemir F, Keul H, Mourran A, Moeller M., Macromol Rapid Commun. 2011, 32(13):1007-13

13

Figure 2. The dependence of ion conductivity on the RH.

NANO-CHANNEL FORMATION BY WEDGE-SHAPED

SULFONATES AND THEIR ION-CONDUCTIVITY STUDY

Heng Zhang1, Jaime J. Hernandez Rueda2, Dimitri A. Ivanov2, Xiaomin Zhu1 1 DWI an der RWTH Aachen e.V. and Institute of Technical and Macromolecular

Chemistry at RWTH Aachen. Forckenbeckstrasse 50, D-52056 Aachen, Germany 2 Institut de Sciences des Matériaux de Mulhouse, IS2M CNRS LRC 722

15 rue Jean Starcky, F-68057 Mulhouse, France

Nafion™ is a well-known example of industrially applied ion-conductive membranes [1]. According to Schmidt-Rohr’s structural model of Nafion, an analogous system with nano-channels is generated in our work, and then the conductivity behaviours are investigated. As shown in Figure 1, we synthesized a series of amphiphilic molecules carrying a large hydrophobic rim and a hydrophilic sulfonate group at the tip of the wedge, and they are able to self-assemble to tetramers and stack together in the direction of a column axis, forming the potential nano-channel. A series of lithium / sodium / potassium / caesium 2,3,4- tris(1,1’- acryloylundecyl- 1’-oxy)benzenesulfonate (Li/Na/K/Cs salt) is synthesised according to a literature procedure [2]. By means of polarizing optical microscope (POM) and X-ray measurements, we determine the mesophase structures that Na and K salts are columnar hexagonal (Colh) phases, and Li and Cs salts are both isotropic.

Figure 1. (a) The schematic formation of the nano-channels by wedge-shaped sulfonates. (b) POM images of Na and K salts. (c) X-ray diffractograms of the four salts. Figure 2 shows the ion conductivity of these salts under different relative humidity (RH). At dry state all sulfonates exhibit similar ion conductivity in the order of 10-5 µS/cm and the conductivity increases with the increase of RH. Interestingly, the conductivity growth rate of Na and K salts which form nano-channels in Colh phase is much higher than that of Li and Cs salts which are in the isotropic state. It indicates the nano-channels of the material indeed have a significant influence on the ion conductive properties. [1] S Slade, et al, J. Electrochem. Soc. 2002, 149, A1556-A1564. [2] X Zhu, et al, Chem. Mater. 2006, 18, 4667-4673.

14

Exploring Soft Matter with DNA Tommaso Bellini

Department of Medical Biotechnology and Translational Medicine University of Milan, Italy

Selective interactions of DNA oligomers with designed sequences have been exploited in recent years for the construction of self-assembled multi-strand nano-structures. In parallel, recent observations have revealed that selectivity and self-assembly can be combined to guide short oligomers of DNA toward various forms of long-ranged liquid crystal ordering. In both cases, structures first nucleate because of local Watson-Crick pairing and duplex formation, followed by various hierarchical stages of self-assembly. In this context, I will discuss two lines of results in which DNA emerges as a unique system for the investigation of soft matter. Concentrated solutions of ultrashort DNA and RNA oligomers, down to 6 base pairs in length, may order into chiral nematic and columnar liquid crystal phases. These phases are produced whenever the oligomers pair into double helices that display mutual end-to-end attraction because of staking or pairing interactions. Building on this first observation, we investigated the generality of liquid crystal ordering in more complex solutions of DNA oligomers, including mixtures of natural right-handed DNA duplexes and synthetic mirror-symmetric duplexes, and solutions of DNA oligomers with partially or fully random sequences. These investigations indicate that the formation of liquid crystal is a general and robust tendency in DNA solutions, and have enlightened a variety of mechanism of ordering, some of them relying on defects and non-equilibrium configurations. DNA can also be used to explore soft matter by designing sequences that assemble into multi-strand structures of controlled shape, valence and mutual interactions. We studied the phase diagram of solutions of 3-arms and 4-arms star-shaped DNA constructs with mutual tip-to-tip attractive interactions. We find that both systems display a liquid-vapor-like phase behavior, with a coexistence region terminating, at higher temperature, in a critical point. We find that the coexistence region markedly depends on the valence of the structures, being much smaller for the constructs with smaller valence. While the observed phase diagrams agree with recent theoretical predictions for colloidal solutions of limited valence and short-range interactions, the dynamics of these systems is anomalous and reflects specific features of the free energy involved in the DNA pair formation.

15

DNA Nanogels as Cancerogens Scavengers

Fuat Topuz,1* Smriti Singh,1 Krystyna Albrecht,2 Martin Moeller,1 and Juergen Groll2

1 DWI e.V. and Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Forckenbeckstrasse 50, 52056 Aachen, Germany

2 Department and Chair of Functional Materials in Medicine and Dentistry, University Hospital Würzburg, Pleicherwall 2, 97070 Würzburg, Germany


Polycyclic aromatic hydrocarbons (PAHs) are byproducts of combustion-related pollutants

and identified as carcinogenic, mutagenic, and teratogenic. They bind to DNA forming PAH-

DNA adduct that can further lead to miscoding of DNA and therefore, cell death. In this

study, we successfully scavenged the phenanthrene as a model PAH molecule with DNA

nanogels in aqueous solutions. The nanogels were prepared from double-stranded (ds-) or

single-stranded (ss-) DNA molecules through inverse-miniemulsion in the size range of 200-

400 nm (Figure 1). DNA nanogels were characterized by TEM, SFM, DLS, FE-SEM,

Fluorescence microscopy, and as well as by UV-spectrophotometer. Fluorescence

spectroscopy was used to investigate PAH scavenging capacities of DNA nanogels in aqueous

solutions at different ionic strengths. Moreover, the molecular level chemistry of binding

between phenanthrene and DNA was elucidated by Circular dichroism (CD) analysis.

Depending on DNA conformation in nanogels, they showed different PAH scavenging

capacities.

Figure 1. Cartoon illustration of DNA nanogel preparation through inverse miniemulsion

method.

16


Oriented detection elements in biosensors: site-specific functionalized llama antibody fragments

Anke Kristin Trilling1,2, Han Zuilhof1 and Jules Beekwilder2

1Laboratory of Organic Chemistry, Wageningen University, Wageningen, The Netherlands 2Plant Research International, Wageningen, The Netherlands

A robust detection method that enables a sensitive and reproducible analysis of targets is

the driving force towards biosensors. The on-going miniaturization in this field yields sensors with nanometer-sized dimensions, which limits the size and quantity of deposited detector elements. Llama antibodies are the smallest antibodies available today, and can serve as a detector element for biosensors.

Conventional antibodies are large, complex molecules, but llamas possess smaller heavy chain antibodies. Heavy chain fragments are small in size and easier to engineer. Therefore we aim to couple llama antibody domains (VHHs) oriented onto surfaces.

Fig1: Llama antibodies A: Conventional Immunoglobulin G (IgG) consist of two heavy chains (yellow/red) and two light chains (green/orange). Antigens are bound by VH and VL domain (red/orange). Heavy chain IgG lacks the light chain. Antigens are bound by VHH domain (red). B: Crystal structure of VHH showing the antigen binding site in green. N-terminus is close to the antigen binding site whereas C-terminus is situated at the opposite site.

VHH fragments have been selected and in vivo biotinylation using the BirA enzyme [1]

was performed to functionalize the C-terminus of VHHs. Biotinylated VHH’s can be immobilized in an oriented way onto streptavidin coated surfaces.

To covalently attach VHHs to surfaces, VHH’s have been functionalized with the methionine analog azidohomoalanine [2] to yield azide (N3) bearing VHHs. An azide can selectively react with an alkyne by strain promoted azide-alkyne 1,3-dipolar cycloaddition (SPAAC) [3], known as click chemistry. Selectivity was improved by engineering VHH’s, to obtain one single azide at the C-terminal end. These functionalized VHHs were oriented onto alkyne functionalized surfaces by click chemistry.

In surface plasmon resonance (SPR) analysis orientation of VHHs result in a higher response compared to randomly immobilized VHHs. 1. Saerens et al. 2005 AnalChem 77(23):7547-7555 2. Kiick et al. 2002 Proc Nat AcadSci USA 99(1):19-24 3. Rostovtsev et al. 2002 AngewChem Inter Ed 41(14):2596-2599

17

Self-assembly of liquid crystalline nanostructures in aqueous solution Mark R. Wilson

Department of Chemistry, Durham University, Durham, DH1 3LE, UK

Chromonic mesogens are non-conventional amphiphiles, which self-assemble in aqueous solution to form

aggregate structures: rods, stacks or layers. These aggregates can subsequently self-organise to form

chromonic mesophases. Self-assembly is different to that seen in most conventional amphiphiles: it is

enthalpically-driven and takes place in the absence of a critical micelle concentration.

There is great interest in chromonic systems as materials for the fabrication of new thin films for

biosensors and optical compensators; and also because a better fundamental understanding of chromonic

self-assembly is required to control aggregate structure formation in certain classes of drug molecules.

This talk presents results from molecular simulation studies of chromonic self-assembly at different levels

of detail. Atomistic molecular dynamics simulations of the dye molecule, sunset yellow [1], and the drug

molecule, disodium cromoglycate, determine for the first time the structure and dynamical properties of

chromonic aggregates in aqueous solution. Showing how subtle changes in intermolecular interactions can

change the mode of self-assembly. Coarse-grained models, at the level of dissipative particle dynamics

(DPD), demonstrate how simulation provides a tool to engineer new nanostructures by exploring the role

of molecular shape and interactions in determining the structure of aggregates formed.

References: [1] F. Chami and M. R Wilson, Molecular Order in a Chromonic Liquid Crystal: A Molecular Simulation Study of the Anionic Azo Dye Sunset Yellow, J. Am. Chem. Soc., 132, 7794, (2010).

18

Ionic liquid crystals: towards addressable water

Alexandra Alvarez Fernández,1* Alan E. Rowan,1 Paul H.J. Kouwer1

1 Institute for Molecules and Materials, Department of Molecular Materials, Radboud University Nijmegen, The

Netherlands Liquid crystals are well-known for their optical properties that now are exploited in the multibillion dollar LCD industry. Recently, focus in the liquid crystal field has turned to alternative applications, such as sensors and templated self-organisation [3]. In the latter, the susceptibility towards external fields can be used to address a range of length scales from nanometers to microns. The compatibility issues of liquid crystals with biomolecules [1], [2] required us to redesign a whole new generation of liquid crystalline materials, focussing on transition temperatures and order: ionic liquid crystals. Can we really go to tuneable water?

References: [1] Brake, J. M., Daschner, M. K., Luk, Y. Y. & Abbott, N. L. Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals. Science 302, 2094–2097 (2003). [2] Slavinec, M., Crawford, G. D., Kralj, S. & Zumer, S. Determination of the nematic alignment and anchoring strength at the curved nematic–air interface. J. Appl. Phys. 81, 2153–2156 (1997). [3] Scott J. Woltman, Gregory D. Jay & Gregory P. Crawford. Liquid-crystal materials find a new order in biomedical applications. Nature Materials 6, 929 - 938 (2007) _____________________________________________ * presenting author; E-mail: [email protected]

19

Solubilization of Thermotropic Liquid Crystal Compounds in Aqueous

Surfactant Solutions

Karthik Peddireddy, Christian Bahr

Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Goettingen,

Germany

We study the micellar solubilization of thermotropic liquid crystal compounds by

immersing single drops in aqueous solutions of ionic surfactants. (N-alkyl-

trimethylammonium bromides) For both nematic and isotropic drops, we observe a linear

decrease of the drop size with time as well as convective flows and self-propelled

motions. The solubilization is accompanied by the appearance of small aqueous droplets

within the nematic or isotropic drop. At low temperatures, nematic drops expel small

nematic droplets into the aqueous environment. Smectic drops show the spontaneous

formation of filament-like structures which resemble the myelin figures observed in

lyotropic lamellar systems. In all cases, the liquid crystal drops become completely

solubilized, provided the weight fraction of the liquid crystal in the system is not larger

than a few percent. [1] Due to higher refractive indices of liquid crystals in comparison to

the surrounding water medium and smoothness of smectic filament’s surface, smectic

filaments can be used for light guiding applications.

[1] Karthik Peddireddy, Pramoda Kumar, Shashi Thutupalli, Stephan Herminghaus, and

Christian Bahr, Langmuir, 2012, 28 (34), 12426-12431

Figure: Left image: Self propelled nematic discs in an aqueous surfactant solution. Right

image: A 70 µm smectic filament in an aqueous surfactant solution which further ejects

another smectic filament.

20

Self-Assembling Temperature-Sensitive Colloids for Investigation of Melting, Frustration, and Jamming Phenomena

Arjun G. Yodh

Department of Physics & Astronomy University of Pennsylvania

Philadelphia, PA 19104-6396

Abstract Temperature-sensitive microgel particles present experimenters with a fantastic new variable for creation of novel phases and control of phase transformations. In particular, colloidal particle diameter and colloidal suspension particle volume fraction are readily tuned by small changes in temperature. I will describe experiments from my laboratory which exploit this phenomenon to learn new physics. Recent experiments, for example, permit us to explore first steps of bulk melting in three-dimensional crystals [1], to create geometrically frustrated colloidal ‘anti-ferromagnets’ [2], and to study aging, phonons and rearrangements in disordered (jammed) media [3-6]. [1] A.M. Alsayed, M.F. Islam, J. Zhang, P.J. Collings, A.G. Yodh, Science 309, 1207-1210 (2005). [2] Y. Han, Y. Shokef, A. Alsayed, P. Yunker, T. C. Lubensky, A. G. Yodh, Nature 456, 898-903 (2008). [3] P. Yunker, Z. Zhang, K.B. Aptowicz, A. G. Yodh, Physical Review Letters 103, 115701 (2009). [4] Chen, K., Ellenbroek, W.G., Zhang, Z.X., Chen, D.T.N., Yunker, P.J., Henkes, S., Brito, C., Dauchot, O., van Saarloos, W., Liu, A.J., and Yodh, A.G., Physical Review Letters 105, 025501 (2010). [5] Chen, K., Manning, M.L., Yunker, P.J., Ellenbroek, W.G., Zhang, Z., Liu, A.J., and Yodh, A.G., Physical Review Letters 107, 108301 (2011). [6] Z. Zhang, N. Xu, D.T.N. Chen, P. Yunker, A. Alsayed, K.B. Aptowicz, P. Habdas, A.J. Liu, S. Nagel, and A.G. Yodh, Nature 459, 230-233 (2009).

21

Stabilisation of ordered colloidal structures and deformed defects by

polymerisation of reactive liquid crystalline matrices

Giorgio Mirri;1 Venkata S. R. Jampani;2 Paul Kouwer;1 Igor Muševič2 and Alan Rowan1

1 Radboud University Nijmegen, Heyendaalseweg 135 6525 AJ, Nijmegen (Netherlands)

2 Institut Jožef Stefan, Jamova 39, 1000, Ljubljana (Slovenia)

Colloidal assemblies in anisotropic media are kept together by a balance between repulsive electrostatic interaction and attractive Van der Waals forces. In nematic liquid crystalline matrices colloidal particles can be assembled exploiting the elastic distortion of the nematic director. By means of laser tweezers is possible to guide the assembly process allowing a one-by-one formation of 2D colloidal crystals.[1] However, these assemblies are only stable in the media they are assembled.

We present a new method for the stabilisation of such assemblies based on the polymerisation of the liquid crystalline matrix. Mono and difunctionalised liquid crystalline monomers were dispersed in a nematic liquid crystal (5CB). Silica particles functionalised with a photoinitiator were dispersed in the reactive mixture and assembled using laser tweezers. Irradiation of the cell with UV light yielded an aligned polymeric network which embedded the assemblies and preserved their patterned structure as demonstrated by diffraction of light. The network has been also proven to be thermally stable.

Partial polymerisation of the matrix has also been used to stabilise the deformation of topological defects. The irradiation of the cell for a limited period of time increases the viscosity in particular near the surface that was irradiated allowing the formation of a polymeric layer. Using laser tweezers is possible to pull the topological defect present around a particle and at the same time create a preferential pattern on the polymeric layer where the defect pins, the defect maintained a certain degree of elasticity and when released tended to return to its original position. Further irradiation of the matrix while the defect is pulled induced the complete polymerisation of the matrix stabilising the defect in unconventional fashions.

[1] I. Musevic, M. Skarabot, U. Tkalec, M. Ravnik, S. Zumer, Science 2006, 313, 954-958.

22

SELF-ASSEMBLED BIOMIMETIC CILIA

Mojca Vilfan1, Gasper Kokot1, Natan Osterman1, Blaz Kavcic2, Andrej Vilfan1,3,Igor Poberaj3, and Dusan Babic3

1 J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia2 LPKF Laser & Elektronika, d.o.o., Polica 33, 4202 Naklo, Slovenia

3 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19,1000 Ljubljana, Slovenia

Biological cilia are hairlike protrusions found on surfaces of some microorganisms and onsurfaces of many eukaryotic cells. They interact with surrounding fluid and their coordi-nated asymmetric beating leads to movement of whole organisms (such a Paramecium)or to generation of fluid flow (e. g. in the respiratory tract). Recently, great advanceshave been made in fabrication of biomimetic or artificial cilia. They serve as model sys-tems for studying hydrodynamic phenomena at low Reynolds numbers under controlledconditions, but also as pumps and mixers in microfluidic devices.We created artificial cilia by assembling small superparamagnetic spheres into chains withone end attached to a surface. The cilia were driven by an external magnetic field along atilted cone. We investigated hydrodynamic effects around one beating cilium, pumping offluid over an array of cilia, and hydrodynamic coupling between two neighbouring cilia. Bymapping traces of non-magnetic tracer particles, we were able to determine the effects ofthe asymmetry of the beating pattern, frequency and height above the surface on the fluidvelocity and determine the fluid flow in the pumping direction as well as in the directionperpendicular to it. The obtained results were compared to the predictions of a numericalsimulation and in the case of one cilium also with the analytical far-field expansion. Themeasured values and the theoretical predictions show an excellent agreement.

Figure 1: Artificial cilia were assembled directly with optical tweezers (A) or self assembledin prefabricated trenches (B).

23

Wrinkling Labyrinth Patterns on Elastomeric Janus Particles

A. C. Trindade1, J. P. Canejo1, P. Patrício2, P. Brogueira3, P. I. C. Teixeira2 and M. H. Godinho1

1 Departamento de Ciência dos Materiais and CENIMAT/I3N, Faculdade de Ciências e

Tecnologia, Universidade Nova de Lisboa, Caparica, 2829-516 Caparica, Portugal E-mail: [email protected]

2 Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro, 1950-062 Lisboa (Portugal) and Centro de Física Teórica e Computacional da Universidade

de Lisboa, Avenida Professor Gama Pinto 2, 1649-003 Lisboa, Portugal 3 Departamento de Física and ICEMS, Instituto Superior Técnico, Universidade Técnica

de Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal

We describe a novel, low-cost and low-tech method for the fabrication of

elastomeric Janus particles with diameters ranging from micrometers to milli-

meters. This consists of UV-irradiating soft urethane/urea elastomer spheres and

cylinders, which are then extracted in toluene and dried [1, 2]. The particles are thus

composed of a single material: no coating or film deposition steps are required.

Furthermore, the whole procedure is carried out at ambient temperature and

pressure. Long, labyrinthine corrugations (“wrinkles”) appear on the irradiated

portions of the particles’ surfaces, the spatial periodicity of which can be controlled

by varying the sizes of particles. The asymmetric morphology of the resulting Janus

particles has been confirmed by scanning electron microscopy, atomic force

microscopy, and optical microscopy. Results can be interpreted by assuming that

each particle consists of a thin, stiff surface layer (“skin”) lying atop a thicker, softer

substrate (“bulk”). The skin’s higher stiffness is hypothesized to result from the

more extensive cross-linking of the polymer chains located near the surface by the

UV radiation [3]. Textures then arise from competition between the effects of

bending the skin and compressing the bulk, as the solvent evaporates and the

particle shrinks.

[1] Trindade, A. C.; Canejo, J. P.; Pinto, L. F. V.; Patrıcio, P.; Brogueira, P.; Teixeira, P. I.

C.; Godinho, M. H. Macromolecules 2011, 44, 2220-2228.

[2] Godinho, M. H.; Trindade, A. C.; Figueirinhas, J. L.; Melo, L. V.; Brogueira, P.; Deus,

A. M.; Teixeira, P. I. C. Eur. Phys. J. E 2006, 21, 319.

[3] Trindade, A. C.; Canejo, L. F. V.; Patrıcio, P.; Brogueira, P.; Teixeira, P. I. C.;

Godinho, M. H. Journal of Materials Chemistry (submitted).

24

Optical and shape anisotropic particles

L. Ramon,1 E. Beltran,1 T. Lopez-Leon,2 H. Wilson,1 O. Parri1,* 1 Chilworth Technical Centre, University Parkway, Southampton, SO16 7DQ (UK)

2 Laboratoire Charles Coulomb, Université Montpellier 2 and CNRS, Montpellier, France.

The synthesis of optically and shape anisotropic particles are very interesting form the point of view of optical and electro-optical applications such as scattering polarizers,1 optical switches2 or as actuators.3 Optically anisotropic spherical particles have been synthesized previously using UV-initiated emulsion polymerization,4 thermal dispersion polymerization5 and microfluidics6. However, anisotropic particles usually are prepared by additional techniques like hard-templates, particle stretching, microfluidics or lithographic methods.7

In this work we present particles derived from reactive mesogens (RM) with both optical anisotropy and different defined shapes by two different methods: 1) a novel one-step synthetic procedure based on oil-in-oil emulsion polymerization and 2) by dispersion polymerization. The emulsion polymerization technique leads to spherical, tactoidal or red blood cells-like particles with a well defined alignment of the director which allows us to manipulate the particles upon applying an electric field. By dispersion polymerization we synthesised spherical particles which upon stretching lead to an electrically addressable particle with a high aspect ratio (1:5) and optical anisotropy due to the alignment of the director. The synthetic procedures also allow us to introduce many different polymerizable moieties in the system to improve the functionality of the particles.

References: [1] I. Amimori, J. N. Eakin, G. P. Crawford, N. V. Priezjev, R. A. Pelcovits, in Digest of Technical Papers - Society for Information Display International Symposium 33, 834 (2002). [2] D. R. Cairns, M. Sibulkin, G. P. Crawford, Applied Physics Letters 78, 2643 (2001). [3] T. J. Merkel, K. P. Herlihy, J. Nunes, R. M. Orgel, J. P. Rolland, J. M. DeSimone, Langmuir, 26, 13086 (2010). [4] D. R. Cairns, M. Sibulkin, G. P. Crawford, Applied Physics Letters, 78, 2643 (2001). [5] M. Vennes, S. Martin, T. Gisler, R. Zentel, Macromolecules, 39, 8326 (2006). [6] A. Fernández-Nieves, G. Cristobal, V. Garcés-Chávez, G. C. Spalding, K. Dholakia, D. A. Weitz, Advanced Materials, 17, 680 (2005). [7]T. J. Merkel, K. P. Herlihy, J. Nunes, R. M. Orgel, J. P. Rolland, J. M. DeSimone, Langmuir, 26, 13086 (2010). _____________________________________________ * presenting author; E-mail: [email protected] E. Beltran acknowledges to the Marie Curie (Hierarchy Project FP7) for the financial support.

25

Topological defects and shape-controlled interaction in nematic liquid crystal

M. Nikkhou, 1 M. Škarabot, 1, 2 and I. Muševič1, 2

1 Josef Stefan Institute, Jamova39, Ljubljana, Slovenia

2 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia

We present an experimental analysis of topological defects around the micro-cylinder with normal surface anchoring dispersed in nematic liquid crystal in cell with planar alignment. We have considered two characteristic types of director pattern. First, micro-cylinder orientated along the rubbing direction of a planar nematic cell was used. By temperature quench using the focused laser light in a thin layer of nematic liquid crystal around the micro-cylinder a pair of defect rings with winding number +1/2 and -1/2 encircling the cylinder can be created. Fig.1a presents the time sequence of unpolarized optical micrographs of nematic liquid crystal around micro-cylinder after quench. Second, micro-cylinder orientated perpendicular to the rubbing direction was used. The point hedgehog defect on top of the cylinder has opened into Saturn ring encircling the micro-cylinder along its longer axis. By thermally quenching the Saturn ring can be cut and make loops and point defects, see Fig. 1b. We study the topological charges of loops and point defects in order to show conservation of total topological charge carried by Saturn ring encircling the micro-cylinder.

Fig. 1. (a) Defect rings with opposite topological charge are created by local quench. (b) Saturn ring is cut into loops and point defects by local quench. Red arrows show the rubbing direction. Next the entanglement between micro-cylinder and micro-sphere was studied. The entangled defect ring -1/2 encircled micro-cylinder and micro-sphere in the form of “figure of eight”, “figure of omega”, and “entangled hyperbolic defect”, similar to colloidal dimers in nematic liquid crystal [1]. +1/2 defect ring encircles micro-cylinder and micro-sphere in the form of loop with twist between them (Fig.2).

Fig. 2. -1/2 ring entangled hyperbolic defect and figure of eight and +1/2 ring entangled twisted loop with micro sphere. Red arrow shows the rubbing direction. References: [1] M. Ravnik, M. Skarabot, S. Žumer, U. Tkalec, I. Poberaj, D. Babič, N. Osterman, and I. Muševič, Entangled Nematic Colloidal dimmers and wires, Phys. Rev. Lett. 99, 247801 (2007).

(a)

(b)

0 S 0.13 S 0.26 S 3.8 S

26

Tilings of nematic colloidal platelets

Miha Ravnik1,2, Jayasri Dontabhaktuni2,3, and Slobodan Zumer1,2,3

1 Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia

2 Centre of Excellence NAMASTE, Ljubljana, Slovenia 3 Centre for Modelling Simulation and Design, University of Hyderabad, Hyderabad, India

Colloidal platelets are natural building blocks for the shape-controlled assembly of crystalline and quasicrystalline tilings. Using three-dimensional (3D) numerical modelling based of Landau-de Gennes free energy minimisation, we demonstrate the self-assembly of triangular, square and pentagonal sub-micrometer sized platelets in a thin layer of nematic liquid crystal. Torques acting on individual platelets are calculated, showing that platelets with quadrupolar symmetry (squares, hexagons, etc) are, orientationally , more strongly bound than platelets with dipolar symmetry (triangles, pentagons) which is important for switching applications. Inter-platelet potentials are shown to depend in a complex way on the orientations of the platelets, exhibiting easy and hard reorientation axes and multiple minima. The platelets form stable two-dimensional (2D) packed structures, and depending on the design they can assemble into structures with crystalline or quasicrystalline symmetry.

27

Cholesteric blue phases under confinement and electric field Jun-ichi Fukuda

National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

We will present some of our numerical studies on confined cholesteric blue phases, exotic three-dimensional ordered phases of a highly chiral liquid crystal. We first consider cases where a liquid crystal exhibiting cholesteric blue phases in the bulk is confined in a thin parallel cell whose thickness is of the order of or smaller than the lattice spacing of bulk cholesteric blue phases (a few hunderd nm). We show that, depending on temperature, cell thickness, and anchoring conditions, the liquid crystal shows various defect structures not found in the bulk. They include a hexagonal lattice of Skyrmion excitations, and a regular array of ring defects. We also carry out numerical calculations to examine how a cholesteric blue phase in a cell responds to an applied electric field (now we consider a thicker cell that can accommodate a defect network of a bulk blue phase). We show that the dynamics of disclination lines inherent in bulk cholesteric blue phases depends sensitively on the strength of the electric field and the sign of the dielectric anisotropy. We also demonstrate that the disclination lines under an electric field exhibit non-trivial dynamics when the field is switched off.

28

High-resolution calorimetric studies on liquid crystal transitionsin thin layers

Y. Sasaki,1 V. S. R. Jampani, 1,2 M. Humar,1 and I. Musevic 1,2

1J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia2University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia

It is known that the alignment of liquid crystal (LC) molecules is quite susceptible to thesurface anchoring. The interfacial effect will be pronounced especially when the moleculesare confined in a tiny space. For this reason, surface treatment is always important forthe study of LCs from industrial as well as scientific viewpoints. So far, theoretical pre-dictions show that a confinement of aligned molecules on a treated substrate substantiallyaffects the physical property of LC through the elastic contributions [1-3]. Indeed, it isexperimentally revealed that the LC behavior on aligned surface is significantly differentfrom the bulk. For example, it is clearly shown that an AFM technique can successfullybe applied to the study of interfacial properties [4]. In this work, we study the thermo-dynamic behavior of a thin layer of aligned LC molecules. A high-resolution differentialscanning calorimetric approach is used to investigate the effect of the surface treatmenton the thermal properties of LCs. We examine experimental conditions such as cell designand thermal response due to finite thickness of the substrate. Several types of LC transi-tions are investigated by using a sandwich type cell with uniform thickness. We confirmedthat the specific heat capacity behavior exhibits a significant difference from the bulk dueto the effect of the treated substrate. Details on the experimental investigations will bereported.

[1] P. Sheng, Phys. Rev. Lett. 37, 1059 (1976).

[2] P. Sheng, Phys. Rev. A 26, 1610 (1982).

[3] T. J. Sluckin, A. Poniewireski, Phys. Rev. Lett 55, 2907 (1985).

[4] K. Kocevar, A. Borstnik, I. Musevic, S. Zumer Phys. Rev. Lett. 86, 5914 (2001).

29

Controlling the Pretilt Angle of Nematic Liquid Crystals byObliquely Sputtering Iron Oxide γ-Fe2O3

Wei-Ta Wu1,2, Meng-Chiou Huang2, and C.W. Lai2, Ru-Pin Pan2, Theo Rasing1

1Radboud University Nijmegen, Institute for Molecules and Materials, 6525 AJNijmegen, The Netherlands

2Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan30010, Republic of China

The multi-domain surface alignment is a challenge for liquid crystal display (LCD) man-ufacturing. For the typical velvet rubbing treatment, the generated static electric anddust may cause LCD defeat and for a multi-domain system it is hard to apply. The keytechnique is how to control the pretilt angle precisely in each domain.We coated obliquely an iron oxide thin film on the polyimide-coated ITO glass by usingplasma sputtering. To understand the alignment mechanism, the surface compositionand morphology is examined by X-ray photoelectron spectroscopy (XPS) and atomicforce microscopy (AFM).Using iron oxide as the alignment layer, we found that the pretilt angle could be controlledby tuning the sputtering conditions (sputtering voltage, plasma beam current, and coat-ing time). A simple model can explain the relations between the pretilt angle and thesputtering conditions.

30

Surface induced ordering phenomena at liquid crystal

interfaces laden with surface active molecules

Xunda Feng Max Planck Institute for Dynamics and Self-Organization Am Fassberg 17 Goettingen 37077, Germany [email protected]

Abstract: Thermotropic liquid crystals (LCs) display a rich variety of surface-induced ordering phenomena in the isotropic phase. The surface field, i.e., the interaction between the LC phase and the substrate, is crucial to determine the surface ordering behavior. Herein, we discuss the observation of rich surface phase behavior through the modification of the surface properties of fluid substrates by controlled physical adsorption of surface active molecules. The first part of this presentation focuses on the LC/water interfaces laden with surfactant molecules, and we show that first-order smectic multi-layer and nematic prewetting transitions could be achieved by controlling the coverage of the surfactant molecules at the LC/water interfaces. We present in the second part the competing ordering processes at the LC/air interface laden with a semifluorinated alkane (C18H27-C12F25, H18F12). Gibbs films of H18F12 exhibit a sharp surface freezing at hydrocarbon surfaces, which can be found similarly at the LC surfaces. We show that the surface freezing of H18F12 destroys the smectic surface layering and change the orientation of the nematic surface phase.

31

LIQUID CRYSTALLINE SUPERATOMS

Teresa Lopez-Leon1,2, Christophe Blanc1, Maurizio Nobili1 and AlbertoFernandez-Nieves2

1 Laboratoire Charles Coulomb, CNRS and Universite Montpellier II, Place EugeneBataillon, 34095 Montpellier, France

2Georgia Institute of Technology, School of Physics, 837 State St. NW, 30332 AtlantaGA, United States.

Nematic liquid crystal shells offer an elegant way for imprinting well defined interactionsites on a sphere, since a set of symmetrically positioned topological defects naturallydecorate the ground states of these systems. These defects are a consequence of a fas-cinating interplay between topology and energy that arises when an ordered system isconfined to a space with curvature. The prospect of using these nematic shells as nano-or micro-sized superatoms creates an avenue for the fabrication of new materials withrevolutionary technological applications.

In this talk, I will show recent advances in the field. Microfluidic techniques have allowedthe experimental realization of nematic shells [1]. A precise control in the defect archi-tecture has been achieved by tuning parameters such as shell thickness, anchoring of theliquid crystal at the boundaries, or the type of liquid crystal phase considered [2-4]. Anumber of different defect structures have been engineered, including the sp, sp2 and sp3

symmetries of carbon atoms, which have enormous potential for photonic applications [2].Although a general and robust method for the functionalization of defects has not beendeveloped yet, DNA appears to be a very promising candidate, since it enables controlin the strength, range and reversibility of the eventual interactions between these liquidcrystalline superatoms.

[1] A.S. Utada, E. Lorenceau, D.R. Link, P.D. Kaplan, H.A. Stone, and D.A. Weitz,Monodisperse Double Emulsions Generated from a Microcapillary Device, Science 308,537 (2005).[2] T. Lopez-Leon, V. Koning, K.B.S. Devaiah, V. Vitelli and A. Fernandez-Nieves, Frus-trated Nematic Order in Spherical Geometries, Nature Phys. 7, 391 (2011).[3] T. Lopez-Leon and A. Fernandez-Nieves, Topological Transformations in Bipolar Shellsof Nematic Liquid Crystals , Phys. Rev. E 79, 021707 (2009).[4] T. Lopez-Leon, A. Fernandez-Nieves, M. Nobili and C. Blanc, Nematic-Smectic Tran-sition in Spherical Shells, Phys. Rev. Lett. 106, 247802 (2011).

32

Assembly and Control of 3D Nematic Colloidal Crystals

A. Nych1,2, U. Ognysta1,2, M. Skarabot1,3, M. Ravnik3, S. Zumer3,1, I. Musvevic1,3,

1 J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia2 Institute of Physics, prospect Nauky, 46, Kyiv 680028, Ukraine


Liquid crystal colloids have attracted a lot of attention because strong and highly anisotropicinteraction between the dispersed particles is responsible for big variety of 2D crystallinestructures. Using laser tweezers we successfully assembled in nematic liquid crystal cella stable and regular 3D dipolar colloidal crystal with body-centered tetragonal lattice.The hierarchical assembly protocol is explained in details from building a single dipolarchains to assembling them into 2x2x3 building blocks and finally to building a 6x6x3 3Dcrystal from these blocks. Spatial positions of the particles and liquid crystal orienta-tion was examined using fluorescent confocal polarizing microscopy (FCPM). Effect of anexternal electric field applied to the cell was studied in liquid crystals with different di-electric anisotropy. In positive dielectric anisotropy liquid crystal the 3D colloidal crystaldemonstrates giant electrostriction when an external electric field is applied to the cell.When the 3D crystal is built in negative dielectric anisotropy material, an external electricfield induces a reversible and controllable electro-rotation of the crystal as a whole, withthe rotation angle up to 30◦ possible. We demonstrate that in dual-frequency materialit is possible to observe both phenomena depending on the applied field frequency. Thisdemonstrates a new class of electrically controlled periodic soft matter systems.

33

Nanocolloids interactions in nematic liquid crystal

A.V. Ryzhkova1, * and I. Muševič1, 2

1J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 2 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana,

Slovenia

The development of modern technologies and tendency in miniaturisation of optical and electronic devices lead to significant increase of the scientific interest in studies of nanometer scale system that can be controllably self-assembled in space. Formation of precisely arranged aggregations can provide new types of material (such as 3D photonic crystals and metamaterials) with controllable electric, optical, chemical and other properties [1-3]. One of the self-assembling mechanisms is based on forces between particles, mediated by the nematic liquid crystal (NLC). In this work the self-organisation of nanocolloids and nanocolloids interaction with defects in nematic liquid crystal pentylcyanobiphenyl (5CB) has been studied. We investigated the influence of particle size (from 450 nm to 22 nm diameter) on interparticle forces as well as on binding energy with topological defects. We have found that fluorescent silica particles, surface-functionalized with N,N-dymethil-N-octadecil-3-aminopropyl trimethoxysilyl chloride (DMOAP) induce dipole and quadrupolar defects around colloids in 5CB. The nanoparticles dynamics and interactions were investigated with several techniques: bright- and dark field microscopies, fluorescent microscopy, crossed-polarized light microscopy. We found that the dark field microscopy is superior for the observation of smallest colloids in the range of 20 nm. We found that binding energy

of 35 nm-450 nm dipolar particles is high enough for stable colloidal assembly. Colloids around 22 nm in diameter do not form stable structures due to the high influence of thermal fluctuations. The interparticle interactions as well as the interactions of individual colloids with topological defects are studied. The possibility of superhierarchical structures generation is discussed.

a) b) c) d)

Fig. 1. Small 500 nm colloids are attracted into Saturn ring (a-b) and point defect (c-d) of 10 µm colloid. (a, c) bright light image; (b, d) fluorescent image.

References: [1] M. Škarabot and I. Muševič, Soft Matter, 6, 5476-5481 (2010). [2] M. Škarabot, M. Ravnik, S. Žumer, U. Tkalec, I. Poberaj, D. Babič and I. Muševič, Physical Review E, 77, 061706 (2008). [3] G. M. Koenig , R. Ong, A. D. Cortes, J. A. Moreno-Razo, J. J. de Pablo and N. L. Abbott, Nano Lett., 9 (7): 2794-801 (2009). * e-mail: [email protected]

34

http://www.ncbi.nlm.nih.gov/pubmed/19459705�


PPOOSSTTEERRSS

35

P. van der Asdonk,‡ D. Voerman, B.E.I. Ramakers, D.W.P.M. Löwik, J.C.M. van Hest, A.E. Rowan, P.H.J. Kouwer*

Institute for Molecules and Materials, Radboud University Nijmegen, The Netherlands

One of the current challenges in materials science is to gain control over nanoscale architectures at the macroscopic level. In many fields of application, ranging from molecular (opto)electronics (organic solar cells, OLED, OFET) to biomimicry (tissue engineering, bone mineralization), device performance benefits from macroscopic organization, which is difficult to achieve via molecular bottom-up assembly.

We propose a novel approach towards this goal by demonstrating the potential of a liquid crystal template as a tool to achieve control over nanoscale architectures up to a macroscopic level. As an example, we investigated the self-assembly process of peptide amphiphiles in an anisotropic medium. Peptide amphiphiles form (isotropic) assemblies of supramolecular nanofibers in water. They are promising materials for applications in tissue engineering, cell differentiation and bone mineralization [1,2]. Many of these potential applications require control over the direction of growth of these nanofibers on a macroscopic scale [3]. Here, we present the controlled self-assembly and polymerization of peptide amphiphiles in the lyotropic chromonic liquid crystal DSCG (disodium cromoglycate) in the nematic phase. Single domain square centimeter samples were prepared where the planar aligned lyotropic chromonic liquid crystals directed the formation of aligned fiber bundles. Qualitative results were obtained from microscopy studies (Figure 1 and 2) and polarized UV-Vis spectroscopy. We believe that this approach can be generalized and that liquid crystal templates are very promising as a tool to achieve control over nanoscale architectures up to a macroscopic level.

Figure 1: Optical micropscopy image of bundles of fibers (present in planar aligned nematic DSCG). Fiber bundles are aligned along the rubbing direction.

Figure 2. SEM image of aligned fiber bundles after removal of DSCG.

[1] J.D. Hartgerink, E. Beniash, S.I. Stupp, Science 294, 1684 (2001).[2] G.A. Silva, C. Czeisler, K.L. Niece, E. Beniash, D.A. Harrington, J.A. Kessler, S.I. Stupp, Science 303, 1352 (2004).[3] J.B. Matson, S.I. Stupp, Chem. Commun. 48, 26-33 (2012).

_____________________________________________‡ presenting authors; E-mail: [email protected]

DIRECTED MACROSCALE SELF-ASSEMBLY OF PEPTIDE AMPHIPHILE NANOFIBERS THROUGH LIQUID CRYSTAL TEMPLATING

37

mailto:[email protected]

mailto:[email protected]

MIXTURES OF MAGNETIC NANOPARTICLES AND THEFERROELECTRIC LIQUID CRYSTALS: NEW SOFT

MAGNETOELECTRICS

Brigita Rozic1,2, Marko Jagodic3,4, Saso Gyergyek1, George Cordoyiannis4, ZvonkoJaglicic3,5, Samo Kralj6, Vassilios Tzitzios7 and Zdravko Kutnjak1,2

1 Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia2 Centre of Excellence Namaste, Jamova cesta 39, 1000 Ljubljana, Slovenia

3 Institute of Mathematics, Physics and Mechanics, Jadranska 19, 1000 Ljubljana,Slovenia

4 EN-FIST Centre of Excellence, Dunajska 156, 1000 Ljubljana, Slovenia5 Faculty of Civil and Geodetic Engineering, Jadranska 19, 1000 Ljubljana, Slovenia

6 Faculty of Natural Science and Mathematics, Koroska cesta 160, 2000 Maribor,Slovenia

7 National Centre for Scientific Research Demokritos, Aghia Paraskevi 15310, Greece

Magnetoelectric materials have recently attracted considerable attention of the scientistsdue to their properties and also due to their potential for applications, for example, in theinformation-storage industry [1]. Recently the development of a soft material based onmixtures of a liquid crystal (LC) and magnetic nanoparticles (MNPs), which would showmagnetoelectricity, has become a holy grail due to the difficult production of the stableLC-NPs mixtures. It is difficult to avoid the separation of the MNPs from the mixture. Inthis work the theoretical estimation and experimental observation of the magnetoelectriceffect in soft composite materials prepared as a mixture of MNPs and ferroelectric LCwill be presented. Three similar systems of two different ferroelectric LCs, i.e., SCE9and Felix 015/100 and two different ferromagnetic NPs, i.e., maghemite and magnetiteNPs were investigated. NPs were weakly anisotropic with a diameter typically around20 nm and coated with an oleic acid to form well dispersed, practically aggregation freedispersion, which was stable for several months. The high resolution calorimetry, di-electric spectroscopy and magnetic susceptibility measurements were investigated in thevicinity of the ferroelectric phase transition. Using the high resolution calorimetry thesimilar disordering effects on the ferroelectric phase transition were found as in case ofthe aerosil particles [2] and the impact of the magnetic nanoparticles on the Goldstoneand soft mode dielectric response was observed. Measurements of the impact of the elec-tric field on the magnetic susceptibility via SQUID susceptometer confirmed the indirectcoupling between the LC’s electric polarization and the NP’s magnetic moments. All ourstudies on ferroelectric LC and MNPs mixtures [3] provide strong support for general be-havior in such mixtures. This demonstrates the possibility to engineer the soft compositemagnetoelectrics from mixtures of magnetic NPs and the ferroelectric LCs.

[1] W. Erenstein, N. D. Mathur, J. F. Scott, Nature 442, 05023 (2006).[2] G. Cordoyiannis, G. Nounesis, Z. Kutnjak, S. Zumer, PRE 75, 021702 (2007).[3] B. Rozic, M. Jagodic, S. Gyergyek, S. Kralj, V. Tzitzios, Z. Jaglicic, Z. Kutnjak,Ferroelectrics, in press.

38

Defect trajectories in nematic shells

David Sec1, Miha Ravnik1,2, and Slobodan Zumer1,2,3


2 Center of Excellence NAMASTE, Jamova 39, 1000 Ljubljana, Slovenia3 Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Nematic liquid crystal in spherical shells exhibit various defect configurations. Whenthe surfaces prefer the tangential ordering of the molecules, the total topological chargemust be +2 and commonly four +1

2defect lines are observed. By chemically functional-

izing these defects one could fabricate colloids with tunable valence, e.g. the tetrahedralposition of the defects could emulate the sp3 structure [1]. Controlling the directional-binding capabilities via defect transformation trajectories would provide a route towardscontrolled self-assembly of colloids for photonic applications.

Here, we demonstrate a numerical study of the interplay of elastic anisotropy and eccen-tricity in spherical shells of non-homogeneous thickness. We show that different stable andmeta-stable director and defect shell states occur when driving the system along distincttransformation trajectories [2]. By comparing the computer simulations to experimentswe show the roles of nematic elastic constant anisotropy and finite shell thickness on thepositions of the defects. In non-concentric shells (the top of the shell is much thinnerthan the bottom) all four defect lines are positioned in the thinner region to minimize thedefect length. The elastic constant anisotropy that could experimentally be controlled byvarying the temperature then gradually changes the positions of the defects in a notablyasymmetric way. On the other hand, when the eccentricity of the shells is changed, thedefects increase their separation in a roughly symmetric way.

[1] T. Lopez-Leon, V. Koning, K. B. S. Devaiah, V. Vitelli, and A. Fernandez-Nieves,Frustrated nematic order in spherical geometries, Nat. Phys. 7, 391 (2011).[2] D. Sec, T. Lopez-Leon, M. Nobili, C. Blanc, A. Fernandez-Nieves, M. Ravnik, andS. Zumer, Defect trajectories in nematic shells: Role of elastic anisotropy and thicknessheterogeneity, Phys. Rev. E 86, 020705 (2012).

39

Novel Elastin-Based Hydrogels with Metal-Free Click Reactivity

Fuat Topuz,1* Martin Moeller,1 and Juergen Groll2




In this study, we present a novel cross-linking approach for elastin polypeptides through

biocompatible isocyanate-terminated hydrophilic cross-linkers. Dynamic rheological

measurements performed during the cross-linking of elastin polypeptides at varied

composition of precursors (both elastin and cross-linker) and at different pH of

polymerization media show the formation of strong to weak elastin hydrogels. Dynamic

mechanical analysis (DMA) operating in the compression mode show that hydrogels can be

compressed up to 70 % of its length with a breaking stress of about MPa level. Further, the

hydrogels showed strain-stiffening behavior so that they resist to small deformations to

protect tissue integrity. Indirect cell cytotoxicity and enzyme-mediated degradation studies

showed that elastin hydrogels were cytocompatible and can be partly degraded by pancreatic

enzyme, elastase. Inner-morphology of hydrogels was explored by SEM analysis revealed that

the pore sizes were mainly influenced by cross-linking density. Lastly, multifunctionable

structure was showed by incorporating the cyclooctyne ligands to the network and further

reactivity was proved with azide-containing fluorescence dye. Cytocompatibility with

intrinsic strain-hardening duplicates the mechanical properties of soft tissues being candidate

as an ideal injectable scaffold for tissue engineering applications.

40


Selective Tethering of Ligands and Proteins on sPEG Layers through

Metal-Free Click Ligation

Fuat Topuz,* and Martin Moeller

DWI e.V. and Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Forckenbeckstrasse 50, 52056 Aachen, Germany


Antiadhesive coating is of interest of biotechnology due to its inertness towards biological

molecules and cells. Controlled functionalization of these surfaces (e.g., through click

chemistry) provides excellent two-dimensional (2D) environments for effective and selective

immobilization of desired molecules. In this manner, we designed star PEG-based thin

hydrogel layers possessing cyclooctyne reactivities for the site-specific tethering of azide

functional molecules in a controlled manner through strain-promoted azide-alkyne

cycloaddition (SPAAC). Thin hydrogel layers were prepared from NCO-terminated star PEG

prepolymers in aqueous solutions through spin coating process. Functionality was formulated

via three different approaches, namely; i) mix-in method; mixing of NCO-sPEG with

bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN-OH) before coating, ii) incubation method;

incubating of freshly prepared surfaces in a aqueous solution of BCN-OH, and iii) using

orthogonal functional star molecules comprising NCO and cyclooctyne reactivities. Resulting

functional layers were investigated through X-ray photoelectron spectroscopy (XPS), infrared

spectroscopy (IR), scanning force microscopy (SFM), contact angle, ellipsometry, and optical

microscopy. Specific binding of proteins onto layers was explored with Surface Plasmon

Resonance (SPR). Results showed that the resulting functional layers were good in prevention

of unspecific protein adsorption, and were reactive towards azide-carrier peptides and proteins

enabling site-specific immobilization of desired biological molecules in a controlled manner.

This promising method can be applied to wide range of diagnostics tests due to the superioties

of sPEG hydrogel layer; e.g. antiadhesivity and biocompatibility.

41


Tailoring Hydrophilicity and Non-Adhesivity of Star-Shaped Poly(ethylene

oxide) Ultrathin Coatings by Terminal Group Modification

Fuat Topuz,1* Peter Gasteier,1 Martin Moeller,1 and Juergen Groll2




Present study reports the tailoring of hydrophilicity and non-adhesivity of PEO-based

ultrathin hydrogel coatings through terminal group modification of coating precursors. The

layers were prepared by mixing of isocyanate (NCO)- and hydroxyl (OH)-terminated star

shaped prepolymers with a backbone consisting of 80% EO (ethylene oxide) and 20% PO

(propylene oxide) (sP(EO-stat-PO)) at varied compositions in pure organic solvent (THF),

and in aqueous solution through spin coating process (Figure 1). The layers were investigated

by contact angle measurements, coating thickness, and homogeneity. The non-adhesive

property of the coatings was explored through serum albumin adsorption and cell adhesion

experiments. The results showed that increasing of OH-terminated sP(EO-stat-PO) content on

coating preparation significantly increase hydrophilicity and decrease the non-specific

protein adsorption and cell adhesion.

Figure 1. Cartoon illustration of thin hydrogel layer formation from both OH and NCO-sP(EO-stat-PO) prepolymers.

42


Physically Cross-Linked Fibrin(ogen) Hydrogels with Tailorable

Mechanical and Biological Properties

Fuat Topuz,1* Lisanne Rongen,2 Arpit Bajpai,2 Stefan Joechenhoevel,2 Juergen Groll,3 and Martin Moeller1


2 Institute of Applied Medical Engineering, Helmholtz Institute of RWTH Aachen University

and Hospital, Forckenbeckstrasse 20, 52062, Aachen, Germany



Fibrin(ogen) with intrinsic physical and biological characteristics plays prominent role in

various pathological processes, including thrombosis adhesion, hemostasis, and platelets

aggregation, and therefore have been used extensively as biomaterials of various shapes and

forms. In this study, we concerned on physically cross-linked fibrin(ogen) hydrogels with

tailorable physical characteristics and biological activities. The hydrogels were prepared

either by Ca2+ or thrombin or both together. Hydrogels were fabricated at different

composition of precursors, and the resulting networks were characterized by the terms of

rheology, swellability, morphology, degradability, and followed by structural analysis through

circular dichroism (CD) analysis while the biological activity of hydrogels was evaluated

through cell viability (proliferation) experiments using Human umbilical vein endothelial

cells (HUVECs). Viscoelastic properties of the gels were measured with a rheometer and

were correlated with structural features of the networks. Results showed that the mechanical

properties of highly swellable physical-fibrin gels could be tailored by the contents of

fibrinogen and Ca2+ ions and with thrombin ratio, and also strongly dependent on fibrin fiber

thickness and cross-linking density. Tailoring the mechanical properties of fibrin gels induced

by physical cross-linking did not affect significantly the biological activity in the studied

range. It was also shown that the physical-fibrinogen hydrogels induced by Ca2+ ions alone

can also bind to HUVECs but not trigger the proliferation.

43


Injectable Tough Laponite/sP(EO-stat-PO) Scaffolds with Metal-Free Click Reactivity

Fuat Topuz,1* Matthias Bartneck,2 Yu Pan,2 Frank Tacke,2 Martin Moeller,1 and Juergen Groll3





Herein, we present functional nanocomposite hydrogels derived from star shaped macromers

and Laponite clays with metal-free click reactivity. Nanocomposite hydrogels produced by

cross-linking of isocyanate-terminated six armed star shaped macromers (NCO-sP(EO-stat-

PO), Mw = 18 kDa or 12 kDa) in the presence of Laponite RDS clays in water and in PBS (pH

= 7.4) at 37 oC. Terminal isocyanate (NCO) groups hydrolyzed to amino groups and then,

these groups reacted quickly with isocyanates forming a stable and biocompatible urea

linkage, while Laponites act as multiple cross-linking domains. By adopting appropriate

synthetic conditions and with tuning the clay and monomer concentrations, weak to strong

hydrogels were obtained. In parallel to chemically cross-linked hydrogel systems, physically

cross-linked gels were produced by hydroxyl-terminated sP(EO-stat-PO) macromers and

Laponite clays and their properties were compared with corresponding chemically cross-

linked hydrogels. The hydrogels were investigated through rheological analysis, dynamic

mechanical analysis (DMA), tensile measurements, swelling, and scanning electron

microscopy (SEM). Since, isocyanates are reactive towards a variety of groups including

amines, thiols, alcohols, functional tough network with bioactive ligands (cell binding

peptide, GRGDS) and specific reactive group (cycloocytne, for metal-free click ligation) were

successfully prepared. Cytocompatibility of hydrogel system was shown over cell viability

experiments with eGFP fluorescently labeled mouse-derived macrophages.

44


List of participants

1 Alexandra Alvarez Fernandez 2 Amir Asgharsharghi 3 Andreja Jelen 4 Andreja Sarlah 5 Andriy Nych 6 Anke Kristin Trilling 7 Anna Ryzhkova 8 Anupam Sengupta 9 Arjun G. Yodh

10 Bernarda Urankar 11 Brigita Rožič 12 Christian Bahr 13 David Seč 14 Etienne Brasselet 15 Firat Ozdemir 16 Fuat Topuz 17 Giorgio Mirri 18 Graham M. Smith 19 Gregor Skacej 20 Helena Godinho 21 Heng Zhang 22 Igor Muševič 23 Ivan I. Smalyukh 24 Janez Pirš 25 Jun-ichi Fukuda 26 Karthik Reddy Peddireddy 27 Laura Cattaneo 28 Liang-Chy Chien 29 Mark R. Wilson 30 Maryam Nikkhoo 31 Matjaž Humar 32 Miha Čančula 33 Miha Ravnik 34 Miha Škarabot 35 Mojca Vilfan 36 Moonsoo Park 37 Mourran Ahmed

38 Natan Osterman 39 Owain Parri 40 Paul Kouwer 41 Peng Huang 42 Pim van der Asdonk 43 Sergey Semin 44 Slobodan Žumer 45 Teresa Lopez-Leon 46 Tine Porenta 47 Tommaso Bellini 48 Uliana Ognysta 49 Uroš Tkalec 50 Venkata Subba Rao Jampani 51 Wei-Ta Wu 52 Xunda Feng 53 Yuji Sasaki 54 Zoran Arsov

45

Workshop on assembling of superstructures in soft matter BOOK OF

Documents

Transcript of Workshop on assembling of superstructures in soft matter BOOK OF