Post on 24-Dec-2015
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
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