Techniques for Polymer Modification

Behzad PourabbasSahand University of Technology

Tabriz-Iranpourabas@sut.ac.ir

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Syllabuses

1. Surfaces and Interfaces2. Molecular Interactions3. Thermodynamics of Surfaces and Interfaces4. Characterization Methods of Surfaces5. Reaction On Polymers6. Polymer Degradation7. Biological Modification of Polymer Surfaces8. Plasma Modification of Surfaces9. Surfactant-Polymer Surfaces

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References

You will have a CD full of Electronic Resourses

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Surfaces and Interfaces

Behzad PourabbasSahand University of Technology

Tabriz-Iran

God made solids, but surfaces were the work of the devil------Wolfgang Pauli

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Surfaces to Ponder

www.stocksurfaces.com. http://strangepaths.com/

http://www.physik.uni-marburg.dehttp://www.physics.upenn.edu

http://plus.maths.org

Overview

Importance of surfaces◦What is a surface?

Surface structure Surface processes Surface interfaces Surfaces in nature Measuring surfaces Modifying surfaces

Importance of Surfaces

Materials Touch on SurfacesCatalysts act from surfacesBiological reactions (life) occur on the

surfacesOn the surfaces: Tribology - friction,

lubrication and wearMost metals are weak on the surfaces

(corrosion)

Surfaces Defined

Different material create surfaces which are interfaces indeed:◦ Solid / air◦Solid / liquid◦Solid / solid◦Liquid / air◦Liquid / liquid◦Liquid / solid

Molecules and colloids / particles have surfaces, surface charges, etc. This is what drives proteins to spontaneously fold (surface energy with water)

Surfaces and Phases

Surface has an Energy:◦Free energy must be minimized

Energy drives most surface reactions◦Passivation◦Oxidation ◦Adsorption of hydrocarbon and water◦Reconstruction and reorientation

Water Phase Diagramhttp://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html

CO2 Phase Diagram

http://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html

HeterogeneousSurface Structure

Surface formation at different length scales: Diffusion Layershttp://www.uni-regensburg.de/Fakultaeten/nat_Fak_I/Mat8/lst/spp/projectSPP1095solidification.html

Real Surfaces Explained

Interfaces: DiscontinuitiesBonds: Dangling bonds, attractive / repulsive

forces, unit cell cleavage planesElectron scattering: Surfaces can scatter

electronsFailure starts on the surfaces:

◦Cracks have surfaces: cohesive / adhesive failures

On Very Important surface: Silicon Surface Planes

Model of the ideal surface for Si{111}1x1.The open and closed circles represent Si atoms in the first and second layers, respectively.Closed squares are fourth-layer atoms exposed to the surface though the double double-layer mesh.The dashed lines indicated the surface 1x1 unit-cell.

http://www.matscieng.sunysb.edu/leed/trunc.html

Silicon Surface viewed by STM

http://www.chm.ulaval.ca/chm10139/

Scanning tunnelling microscope image of a Si surface, ~0.3° off (100) orientation showing the type A steps (Si dimers parallel to steps) and type B steps (Si dimers perpendicular to steps). Uppermost part of the surface is at lower right, with downward tilt to upper left. Scale is ~110 nm square (Prof. Max Lagally).

Surface Processes

Passivation◦Oxide formation◦Adventitious carbon

Reconstruction◦Crystalline◦Polymer orientation

Adsorption of gases and water vapor◦Both can lead to surface passivation

Free energy at the surface. The excess energy is called surface free energy and can be

quantified as a measurement of energy/area. It is also possible to describe this situation as having a line tension

or surface tension which is quantified as a force/length measurement.

Surface tension can also be said to be a measurement of the cohesive energy present at an interface.

The common units for surface tension are dynes/cm or mN/m. Solids may also have a surface free energy at their interfaces but

direct measurement of its value is not possible through techniques used for liquids.

Surface Free Energy

Polar liquids, such as water, have strong intermolecular interactions and thus high surface tensions.

Any factor which decreases the strength of this interaction will lower surface tension.

Thus an increase in the temperature of this system will lower surface tension.

Any contamination, especially by surfactants, will lower surface tension.

http://www.ksvinc.com/surface_tension.htm

Surface Free Energy

Surface Energetics

The unfavorable contribution to the total (surface) free energy may be minimized in several ways: 1.By reducing the amount of surface area exposed –

this is most common / fastest2.By predominantly exposing surface planes which

have a low surface free energy 3.By altering the local surface atomic geometry in a

way which reduces the surface free energy

Surface Tension

http://www.sciencekids.co.nz/

http://hyperphysics.phy-astr.gsu.edu/

Surface Tension

The molecules in a liquid have a certain degree of attraction to each other. The degree of this attraction, also called cohesion, is dependent on the properties of the substance. The interactions of a molecule in the bulk of a liquid are balanced by an equally attractive force in all directions. The molecules on the surface of a liquid experience an imbalance of forces i.e. a molecule at the air/water interface has a larger attraction towards the liquid phase than towards the air or gas phase. Therefore, there will be a net attractive force towards the bulk and the air/water interface will spontaneously minimize its area and contract.

http://www.ksvinc.com/LB.htm

Surface Tension

The storage of energy at the surface of liquids. Surface tension has units of erg cm-2 or dyne cm-1. It arises because atoms on the surface are missing bonds. Energy is released when bonds are formed, so the most stable low energy configuration has the fewest missing bonds. Surface tension therefore tries to minimize the surface area, resulting in liquids forming spherical droplets and allowing insects to walk on the surface without sinking.

 

                                                          

http://scienceworld.wolfram.com/physics/SurfaceTension.html

Surface Tension in Actionhttp://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html

Molecular adsorption to Surfaces?

There are two principal modes of adsorption of molecules on surfaces: Physical adsorption ( Physisorption ) Chemical adsorption ( Chemisorption ) The basis of distinction is the nature of the bonding between the

molecule and the surface. With: Physical adsorption : the only bonding is by weak Van der Waals -

type forces. There is no significant redistribution of electron density in either the molecule or at the substrate surface.

Chemisorption : a chemical bond, involving substantial rearrangement of electron density, is formed between the adsorbate and substrate. The nature of this bond may lie anywhere between the extremes of virtually complete ionic or complete covalent character.

http://www.chem.qmul.ac.uk/surfaces/scc/

Adsorption / Self Assembly Processes on Surfaces

Physisorption◦Physical bonds

Chemisorption◦Chemical bonds

Self-Assembled Monolayers (SAMs)◦Alkane thiols on solid gold surfaces◦Self assembly of monolayers

Chemi / Physi - Adsorption

The graph above shows the PE curves due to physisorption and chemisorption separately - in practice, the PE curve for any real molecule capable of undergoing chemisorption is best described by a combination of the two curves, with a curve crossing at the point at which chemisorption forces begin to dominate over those arising from physisorption alone. The minimum energy pathway obtained by combining the two PE curves is now highlighted in red. Any perturbation of the combined PE curve from the original, separate curves is most likely to be evident close to the highlighted crossing point.

http://www.chem.qmul.ac.uk/surfaces/scc/scat2_4.htm

Structure of Polymeric Surfaces

http://www.nanofolio.org/images/gallery01/

AFM of a thin film of a block copolymer - a molecule with a long section that can crystallise (polyethylene oxide), attached to a shorter length of a non-crystallisable material (poly-vinyl pyridine). What you can see is a crystal growing from a screw dislocation. The steps have a thickness of a single molecule folded up a few times.

Structure of Polymeric Surfaces Atomic force microscopes

are ideal for visualizing the surface texture of polymer materials. In comparison to a scanning electron microscope, no coating is required for an AFM. Images A, B, and C are of a soft polymer material and were measured with close contact mode. Field of view: 4.85  µm × 4.85 µm

http://www.pacificnanotech.com/polymers_single.html

Polymer Surface Orientation

AFM of polymer surface showing molecular orientation.

Note the change in scale of the scanning measurement.

Polymers can ‘reorient’ over time to reduce surface energy (like a self-assembly process)

http://www.msmacrosystem.nl/3Dsurf/Shots/screenShots.htm

Ozone Treated Polypropylene

Ozone treated polypropylene showing the affect of energetic oxygen etching of the polymer, and loss of fine structural filaments.

AFM images and force measurements show increase in surface energy, as well as an increase in surface ordering of the filaments.

http://publish.uwo.ca/~hnie/sc2k.html

Surface Interfaces

Every interface has two surfaces◦Solid / air◦Solid / liquid◦Solid / solid ◦Liquid / air◦Liquid / liquid◦Liquid / solid

Interesting things happen at interfaces! Like the start of life!~99% of living organisms live in the top 1cm of the ocean

Forces at Interfaces

Van Der Val's forcesSurface tensionInterfacial bondingHydrophobic / hydrophilic interactionsSurface reconstruction / reorientationDriven by, or are part of ‘excess surface free

energy’ which must be minimized.

Importance of Interfaces

Chemical reactions occur at interfaces◦Particularly corrosion

Scattering energy◦Electrons◦Light◦Phonons

An interface is actually two surfaces

Defects at Interfaces

Missing atoms◦Defects and holes

Extra atoms◦Surface segregation

Dangling bonds◦Disrupted electronic properties

Dimensional issues◦Lattice mismatch / shelves

Cohesive Failure

Material A

Material B

Material B

Material fails cohesively within B

Adhesive Failure

Material A

Material B

Material fails adhesively between A and B

Adhesive Failure (Craze)

Schematic representation of the structure at the crack tip in a crazing material are shown at three length scales. It is assumed that only material A crazes. The whole of the craze consists of lain and cross-tie fibrils.

http://www.azom.com/details.asp?ArticleID=2089

Surface Reactions

OxidationSurface diffusionDiffusion and oxidationAdventitious carbon bonding

◦Hydrocarbons from the atmosphereSurface rearrangement

◦Polymers may reorient to minimize energy

A Typical Surface

Solid material like silicon or aluminum

Oxide layer of about 15 to 20 Angstroms

Hydrocarbon layer of about 15 to 20 Angstroms

Hydrocarbons and water rapidly adsorb to a metal or Silicon surface. Oxides form to a thickness of about 15To 20 Angstroms, and hydrocarbons to a similar thickness.This is part of the normal surface passivation process.

Langmuir-Blodgett Films

Definition of LB films◦History and development

Construction with LB filmsBuilding simple LB SAMsNano applications of LB films

◦Surface derivatized nanoparticles◦Functionalized coatings in LB films

Langmuir-Blodgett Films

A Langmuir-Blodgett film contains of one or more monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing (or emersing) the solid substrate into (or from) the liquid. A monolayer is added with each immersion or emersion step, thus films with very accurate thickness can be formed. Langmuir Blodgett films are named after Irving Langmuir and Katherine Blodgett, who invented this technique. An alternative technique of creating single monolayers on surfaces is that of self-assembled monolayers. Retrieved from "http://en.wikipedia.org/wiki/Langmuir-Blodgett_film"

Langmuir-Blodgett Films

http://www.ksvltd.com/pix/keywords_html_m4b17b42d.jpg

Deposition of Langmuir-Blodgett molecular assemblies of lipids on solid substrates.

http://www.bio21.bas.bg/ibf/PhysChem_dept.html

Self Assembly

Self-assembly is the fundamental principle which generates structural organization on all scales from molecules to galaxies. It is defined as reversible processes in which pre-existing parts or disordered components of a preexisting system form structures of patterns. Self-assembly can be classified as either static or dynamic.

http://en.wikipedia.org/wiki/Self-assembly

Molecular Self-Assembly Molecular self-assembly is the assembly of molecules without guidance

or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and

intermolecular self-assembly, although in some books and articles the term self-assembly refers only to intermolecular self-assembly.

Intramolecular self-assembling molecules are often complex polymers with the ability to assemble from the random coil conformation into a well-defined stable structure (secondary and tertiary structure). An example of intramolecular self-assembly is protein folding.

Intermolecular self-assembly is the ability of molecules to form supramolecular assemblies (quarternary structure). A simple example is the formation of a micelle by surfactant molecules in solution.

http://en.wikipedia.org/wiki/Self-assembly

Self Assembled Monolayers

SAMs – Self Assembled MonolayersAlkane Thiol complexes on gold

◦C10 or longer, functionalized end groupsCan build multilayer / complex structuresUsed for creating biosensors

◦Link bioactive molecules into a scaffoldThe first cells on earth formed from SAMs

The self-assembly process. An n-alkane thiol is added to an ethanol solution (0.001 M). A gold (111) surface is immersed in the solution and the self-assembled structure rapidly evolves. A properly assembled monolayer on gold (111) typically exhibits a lattice.

The Self-Assembly Process

A schematic of SAM (n-alkanethiol CH3(CH2)nSH

molecules) formation on

a Au(111) sample.

SAM Technology Platform SAM reagents are used for

electrochemical, optical and other detection systems. Self-Assembled Monolayers (SAMs) are unidirectional layers formed on a solid surface by spontaneous organization of molecules.

Using functionally derivatized C10 monolayer, surfaces can be prepared with active chemistry for binding analytes.

http://www.dojindo.com/sam/SAM.html

SAM Surface DerivatizationBiomolecules (green)

functionalized with biotin groups (red) can be selectively immobilized onto a gold surface using a streptavidin linker (blue) bound to a mixed biotinylated thiol / ethylene glycol thiol self-assembled monolayer.

http://www.chm.ulaval.ca/chm10139/peter/figures4.doc

SAMs C10 Imaging with AFM

http://sibener-group.uchicago.edu/has/sam2.html

Multilayer LB Film Process

Smart Materials for Biosensing Devices – Cell Mimicking Supramolecular Assemblies and Colorimetric Detection of Pathogenic Agents

Surface Contamination

All surfaces become contaminated!It is a form of ‘passivation’

◦Oxidation of metals◦Adventitious hydrocarbons◦Chemisorption of ions

It can happen very rapidlyAnd be very difficult to remove

Measuring Surfaces

AFM – Atomic Force MicroscopySEM – Scanning Electron MicroscopyXPS (ESCA) – X-Ray Photoelectron

SpectroscopyAES – Auger Electron SpectroscopySSIMS – Static Secondary Ion Mass

SpectroscopyLaser interferometry / Profilometry

XPS/AES Analysis Volume

Surface Analysis ToolsSSX-100 ESCA on the left, Auger Spectrometer on the right

XPS Spectrum of Carbon

XPS can determine the types of carbon present by shifts in the binding energy of the C(1s) peak. These data show three primary types of carbon present in PET. These are C-C, C-O, and O-C=O

Surface Treatments

Control friction, lubrication, and wear Improve corrosion resistance (passivation)Change physical property, e.g., conductivity,

resistivity, and reflection Alter dimension (flatten, smooth, etc.) Vary appearance, e.g., color and roughness Reduce cost (replace bulk material)

Surface Treatment of NiTi

Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

Surface Treatment of NiTi

Surface Treatment of NiTi

XPS spectra of the Ni(2p) and Ti(2p) signals from Nitinol undergoing surface treatments show removal of surface Ni from electropolish, and oxidation of Ni from chemical and plasma etch. Mechanical etch enhances surface Ni.

Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

Thermal Spray Coating PhotomicrographsPlasma Spray Chromium Oxide Coatings

Plasma Sprayed Chromium Oxide Coatings with base coatings of Hastelloy C for use in very corrosive environments

Thermal Spray Coating PhotomicrographsPlasma Spray Chromium Oxide Coatings

Plasma Sprayed Chromium Oxide Coatings with base coatings of Hastelloy C for use in very corrosive environments

Surface Derivatization

A functionalized gold surface contains a polar amino tail, imparting a hydrophilic character compared to the straight chain alkane thiol. This is an example of a SAM

                                      

             

http://www.dojindo.com/sam/SAM.html

Snow Cleaning with CO2

http://www.co2clean.com/polymers.html

Surfaces in Nature

Cell membranes◦Self-assembled phospholipid bilayers◦Proteins add functionality to the membrane

Skin (ectoderm)Lungs

◦Exchange of O2, CO2, and water vaporCell surface recognition (m-proteins)

◦Major histocompatibility complex

Molecular Self Assembly

3D diagram of a lipid bilayer membrane - water molecules not represented for clarity

http://www.shu.ac.uk/schools/research/mri/model/micelles/micelles.htm

Different lipid model - top : multi-particles lipid molecule

- bottom: single-particle lipid molecule

Cell Membranes

http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/default.htm

Summary

Surfaces are discontinuitiesSurface area creates energyDangling bonds lead to passivationInterfaces are critical to ‘bonding’Surfaces can be modified / derivatizedSurfaces are critical to life

◦All important things happen at a surface!

References

http://www.eaglabs.com/ http://www.ksvinc.com/LB.htm http://www.dojindo.com/sam/SAM.html http://www.co2clean.com/clnmech.htm http://en.wikipedia.org/wiki/Self-assembly http://www.azom.com/default.aspSJSU Biomedical Materials Program