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Stretchable, Transparent, Ionic ConductorsC. Keplinger, J-Y. Sun, C.C. Foo, P. Rothemund, G.M. Whitesides and Z. Suo, Science, 30 Vol 341 no. 6149, 984-987 (2013)

An issue with existing electronic stretchable transparent conductors is their limitation when applied to soft machines and materials. To meet the requirements of the material similar to skin, heart and brain, Zhigang Suo of Harvard School of Engineering and Applied Sciences and his team assembled a stretchable, transparent, ionic conductor. This allows the conductor to mimic the elastic properties of cells and tissues while still maintaining higher resistivity, in a way that existing electronic conductor cannot.

The conductor was designed with two electrodes acting as the conductors, electrolyte elastomers, acting as ionic conductors and forming a double layer with the electrode, as well as a dielectric acting as an insulator. Arrangement can be seen in Fig. 1. Dielectric elastomer was set in between two membranes of electrolytic elastomer, allowing for the desired stretchiness and transparency. A 100-μm-thick polyacrylamide hydrogel with NaCl and a 1-mm-thick very high bond (VHB) tape were used as the electrolyte and dielectric, respectively. Voltage applied between

two electrodes would collect on the two faces of the dielectric with opposite charges, pinching the center and causing it to reduce in thickness and enlarging the area (Fig. 1 Part A,B). A 167% increase to the area was achieved (Fig. 1 Part C,D).

A transparent loudspeaker was built to demonstrate 20 Hz to 20 kHZ sound range. Piezoelectic polymers are commonly used in loudspeakers as the conductors, but replacing them with ionic conductors allows the loudspeaker to be operated with lower electric fields. One drawback to this ionic design is that ionic conductors have lower sheet resistance than some loudspeaker conductors due to the increase in stretching. However, the ionic conductors’ higher resistivity and high stretchability still give a positive outlook for its use in cases that require biocompatibility.

You can read the full paper here in Science magazine.

Marcus Rice

Fig 1: (A) shows the initial set up of the ionic conductor model before any voltage has been applied. The Dielectric elastomer rests in a thick sandwich between the two electrodes. (B) shows the model after voltage has been applied and the dielectric elastomer has expanded outward, increasing the area. (C) Shows the elastomer shaped as a heart before voltage is applied and (D) shows it expanded after the voltage has been applied.

Dear Soft Matter Colleagues,

Welcome to the March 2014 edition of SoftMatterWorld. This month we are featuring two interesting new articles focusing on different novel aspects of polymer science; transparent, ionic conducting polymers and a fascinating model for skin wrinkling! We would also like to let you know about an upcoming soft matter summer school in Corsica, France in addition to many more conferences to remember for the spring/summer season, so mark your calendars.

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Figure 2, (a) Rod packing composed of straight rods. One unit cell of the structure with slightly he-lical filaments and a single helix of the structure shown with unit cell length L and radius R. (b)Total free energy as a function of unit cell size L helix radius R. A path of low total free energy configura-tions is followed by corneocytes as they swell and dry. The lower images show the two states.

Shaping the Skin: The Interplay of Mesoscale Geometry and Corneocyte SwellingMyfanwy E. Evans and Roland Roth, Phys. Rev. Lett. 112, 038102

(2014).

Corneocytes are skin cells comprised of keratin intermediate filaments. This outer layer of our skin reacts to prolonged exposure to water by swelling, forming the wrinkles familiar to most who have spent too long in the water. The expansion required to form these wrinkles exceeds what would be allowed by the elastic extension of the filaments alone. Another mechanism must be at work to account for the phenomenon. It is thought that the filaments are chiral, allowing them to cooperatively unwind and lever off each other. Their arrangement may also be ordered, allowing for the process to be reversible.

Researchers in Germany have devised a model that replicates these observed macroscopic effects. The model consists of helical rods that are varied in unit cell size and in radius (figure 2) suspended in a water-like solvent. They examined the free energy balance for the various configurations.

As seen in in figure 2, the arrangement of the rods follow an ideal path of low total free energy. The researchers show that the elastic energy of the keratin filaments is in near balance with the grand potential energy. Should the elasticity be too great, they would never expand. Likewise, if it was too weak, the corneocytes would always be in their swollen form. The two opposing forces are comparable enough in value that only a small external change is needed to prompt

a shift from one state to the other. The ease of the transition is further helped by the hydrophilic nature of the helical rods. The rods are coated with a thin layer of water, preventing direct contact with each other. This layer also prevents cross-linking, which is often the dominant configuration in similar systems.

Through this model, the authors have demonstrated how small scale structures and patterns can have macro-scale effects on the morphology and behavior of materials. These data may give insights into conditions that affect the skin. For example, the authors suggest dermatitis may be caused by excessive drying and hydrating of the skin, allowing some cross-linking of the keratin intermediate filaments in skin to occur.

You can read the full article here in Physical review Letters

Michael Lane

Summer School Opportunity - Soft-FIRE 2014July 29th - August 8th 2014

Following the first Dynasoft 2008 and 2010 schools, held in August 2008 and August 2010 in Cargèse (Corsica, France), we are pleased to announce the Soft-FIRE Summer School (July 29 – August 8, 2014). This year the school will focus on combining academic lectures and industrial talks.

The aim of the school is to train young researchers in a lecture format, from basic knowledge to state-of-the-art research on a number of rapidly evolving questions. This school aims to promote informal discussions and interactions between researchers.

The school will be held at the Institut d’Etudes Scientifiques de Cargèse (I.E.S.C). The Institute is located near Cargèse, a little village on the west coast of Corsica, 75 km north of Ajaccio. The I.E.S.C. provides a relaxing and enjoyable environment close to the beach and Cargèse.

The school will cover a wide range of soft matter topics, including:

• Soft matter physics

• Soft chemistry

• Microfluidics

• Statistical physics in soft matter

• Polymers for energy

• Drug delivery

• Polymer electronics

• Technical methods

• Biophysics, viruses

• Colloids

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APS Special Session - Collective motion across scales: From proteins to animalsSession J14, Tuesday March 4, 2:30-5:30 p.m. Rooms 301-303,

Colorado Convention Center, Denver, CO

If you will be attending the American Physical Society march meeting this week don’t miss this special invited session on collective motion.

The emergence of collective motion and dynamics across a wide range of length and time scales in biology has inspired research in a multitude of disciplines including biology, physics, mathematics and even robotics. Systems comprising self-propelled individuals or active components with only a few simple interactions can exhibit the formation of striking self-organized dynamic patterns including flocks and swarms. These phenomena occur in a wide variety of systems ranging from biopolymers and photoactivated colloidal particles to swimming bacteria, insects, birds and fish. The implication that there could be universal laws governing such systems and our efforts to understand them have led to a recent surge in the activity in this field. This symposium aims to bring together a mixture of theorists and experimentalists who have worked on multiple aspects of the problem including hydrodynamic foundations, active matter approaches and the role of disorder on systems ranging from microtubules to insects.

The aim of this session is to spark a discussion about the recent advances, outstanding questions and future directions in this field. We also hope to attract many more physicists (both junior and senior, experimentalists and theorists) who already have the appropriate tools of the trade to this fascinating and rapidly growing area at the interface of biological, soft matter and statistical physics.

Thanks for reading

Linda Hirst, Adam Ossowski and The Soft Matter world Team

ConferenceListings dates and deadlnes

8TH INTERNATIONAL SYMPOSIUM ON “MOLECULAR ORDER AND MOBILITY IN POLYMER SYSTEMS”

� Abstract Submission - October 1st � Early Registration – March 10, 2014 � Abstract Submission – March 29, 2014

www.onlinereg.ru/site.php?go=158&page=2670&lang=ENG

INTERNATIONAL CONFERENCE ON INTELLIGENT MATERIALS & NANOMATERIALS – AIMN14

� Deadline for Submission of Full Papers – March 20, 2014

� Deadline for Registration – April 8, 2014http://www.aimn13.org/dates.htm

IOP PRESENTS: ADVANCED SCHOOL IN SOFT CONDENSED MATTER ‘SOLUTIONS IN THE SPRING’

� Abstract Submission Deadline – March 21, 2014

GRC PRESENTS | BIOINSPIRED MATERIALS CONFERENCE AND SEMINAR

� Oral Presentation Consideration Submission – March 21, 2014

� Meeting Application – May 25, 2014http://www.grc.org/programs.aspx?year=2014&program=grs_bioins

IOP PRESENTS: ADVANCED MATERIALS FOR DEMANDING APPLICATIONS

� Early Registration Deadline – March 22, 2014 � Registration Deadline – April 5, 2014

4TH INTERNATIONAL ADVANCES IN APPLIED PHYSICS AND MATERIALS SCIENCE | APMAS 2014

� Abstract Submission Deadline – March 21, 2014