Techniques for Polymer
Modification
Behzad Pourabbas
Sahand University of Technology
Tabriz-Iran
pourabas@sut.ac.ir
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Surfaces and Interfaces
Molecular Interactions
Thermodynamics of Surfaces and Interfaces
Characterization Methods of Surfaces
Reaction On Polymers
Polymer Degradation
Biological Modification of Polymer Surfaces
Plasma Modification of Surfaces
Surfactant-Polymer Surfaces
Syllabuses
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You will have a CD full of Electronic
Resourses
References
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Surfaces and Interfaces
Behzad Pourabbas
Sahand University of Technology
Tabriz-Iran
God made solids, but surfaces were the work of the
devil
------Wolfgang Pauli
5
www.stocksurfaces.com.
http://strangepaths.com/
http://plus.maths.org
http://www.physik.uni-marburg.de
http://www.physics.upenn.edu
Surfaces to Ponder
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Importance of surfaces
◦ What is a surface?
 Surface structure
 Surface processes
 Surface interfaces
 Surfaces in nature
 Measuring surfaces
 Modifying surfaces
Overview
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Materials Touch on Surfaces
Catalysts act from surfaces
Biological reactions (life) occur on the
surfaces
On the surfaces: Tribology - friction,
lubrication and wear
Most metals are weak on the surfaces
(corrosion)
Importance of Surfaces
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Different material create surfaces which are
interfaces indeed:
◦ Solid / air
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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 Defined
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Surface has an Energy:
◦ Free energy must be minimized
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Energy drives most surface reactions
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Passivation
Oxidation
Adsorption of hydrocarbon and water
Reconstruction and reorientation
Surfaces and Phases
Water Phase Diagram
http://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html
CO2 Phase Diagram
http://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html
Heterogeneous
Surface Structure
Surface formation at different length scales:
Diffusion Layers
http://www.uniregensburg.de/Fakultaeten/nat_Fak_I/Mat8/lst/spp/projectSPP1095solidification.html
Interfaces: Discontinuities
 Bonds: Dangling bonds, attractive / repulsive
forces, unit cell cleavage planes
 Electron scattering: Surfaces can scatter
electrons
 Failure starts on the surfaces:
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◦ Cracks have surfaces: cohesive / adhesive failures
Real Surfaces Explained
On Very Important surface:
Silicon Surface Planes
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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 fourthlayer 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
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).
http://www.chm.ulaval.ca/chm10139/
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Passivation
◦ Oxide formation
◦ Adventitious carbon
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Reconstruction
◦ Crystalline
◦ Polymer orientation
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Adsorption of gases and water vapor
◦ Both can lead to surface passivation
Surface Processes
 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
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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 / fastest
2.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 Energetics
http://www.sciencekids.co.nz/
http://hyperphysics.phy-astr.gsu.edu/
Surface Tension
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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
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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.
Surface Tension
http://scienceworld.wolfram.com/physics/SurfaceTension.html
Surface Tension in Action
http://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html
Molecular adsorption to Surfaces?
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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
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Physisorption
◦ Physical bonds
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Chemisorption
◦ Chemical bonds
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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
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 (polyvinyl 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.
http://www.nanofolio.org/images/gallery01/
Structure of Polymeric Surfaces
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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
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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
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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
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Every interface has
two surfaces
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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
Surface Interfaces
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Van Der Val's forces
Surface tension
Interfacial bonding
Hydrophobic / hydrophilic interactions
Surface reconstruction / reorientation
Driven by, or are part of ‘excess surface free
energy’ which must be minimized.
Forces at Interfaces
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Chemical reactions occur at interfaces
◦ Particularly corrosion
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Scattering energy
◦ Electrons
◦ Light
◦ Phonons
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An interface is actually two surfaces
Importance of Interfaces
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Missing atoms
◦ Defects and holes
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Extra atoms
◦ Surface segregation
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Dangling bonds
◦ Disrupted electronic properties
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Dimensional issues
◦ Lattice mismatch / shelves
Defects at Interfaces
Material A
Material B
Material fails cohesively within B
Material B
Cohesive Failure
Material A
Material fails adhesively between A and B
Material B
Adhesive Failure
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.
Adhesive Failure (Craze)
http://www.azom.com/details.asp?ArticleID=2089
Oxidation
 Surface diffusion
 Diffusion and oxidation
 Adventitious carbon bonding
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◦ Hydrocarbons from the atmosphere
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Surface rearrangement
◦ Polymers may reorient to minimize energy
Surface Reactions
Hydrocarbon layer of about 15 to 20 Angstroms
Oxide layer of about 15 to 20 Angstroms
Solid material like silicon or aluminum
Hydrocarbons and water rapidly adsorb to a metal or
Silicon surface. Oxides form to a thickness of about 15
To 20 Angstroms, and hydrocarbons to a similar thickness.
This is part of the normal surface passivation process.
A Typical Surface
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Definition of LB films
◦ History and development
Construction with LB films
 Building simple LB SAMs
 Nano applications of LB films
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◦ Surface derivatized nanoparticles
◦ Functionalized coatings in LB films
Langmuir-Blodgett Films
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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
Deposition of Langmuir-Blodgett molecular assemblies of lipids on solid substrates.
http://www.ksvltd.com/pix/keywords_html_m4b17b42d.jpg
http://www.bio21.bas.bg/ibf/PhysChem_dept.html
Langmuir-Blodgett Films
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. Selfassembly can be classified as either static or
dynamic.
 http://en.wikipedia.org/wiki/Self-assembly
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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
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Self Assembled Monolayers
SAMs – Self Assembled Monolayers
 Alkane Thiol complexes on gold
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◦ C10 or longer, functionalized end groups
Can build multilayer / complex structures
 Used for creating biosensors
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◦ Link bioactive molecules into a scaffold
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The first cells on earth formed from SAMs
A schematic of SAM (nalkanethiol CH3(CH2)nSH
molecules) formation on
a Au(111) sample.
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
SAM Technology Platform
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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 Derivatization
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Biomolecules (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
All surfaces become contaminated!
 It is a form of ‘passivation’
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◦ Oxidation of metals
◦ Adventitious hydrocarbons
◦ Chemisorption of ions
It can happen very rapidly
 And be very difficult to remove
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Surface Contamination
AFM – Atomic Force Microscopy
SEM – Scanning Electron Microscopy
XPS (ESCA) – X-Ray Photoelectron
Spectroscopy
 AES – Auger Electron Spectroscopy
 SSIMS – Static Secondary Ion Mass
Spectroscopy
 Laser interferometry / Profilometry
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Measuring Surfaces
XPS/AES Analysis Volume
Surface
SSX-100
ESCA Analysis
on the left, AugerTools
Spectrometer on the right
XPS Spectrum of Carbon
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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 CC, C-O, and O-C=O
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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 Treatments
Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray
Surface Treatment of NiTi
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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 Photomicrographs
Plasma Spray Chromium Oxide Coatings
Plasma Sprayed Chromium Oxide Coatings with base coatings of Hastelloy C for use in very corrosive environments
Thermal Spray Coating Photomicrographs
Plasma Spray Chromium Oxide Coatings
Plasma Sprayed Chromium Oxide Coatings with base coatings of Hastelloy C for use in very corrosive environments
Surface Derivatization
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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
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Cell membranes
◦ Self-assembled phospholipid bilayers
◦ Proteins add functionality to the membrane
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Skin (ectoderm)
Lungs
◦ Exchange of O2, CO2, and water vapor
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Cell surface recognition (m-proteins)
◦ Major histocompatibility complex
Surfaces in Nature
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
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Surfaces are discontinuities
Surface area creates energy
Dangling bonds lead to passivation
Interfaces are critical to ‘bonding’
Surfaces can be modified / derivatized
Surfaces are critical to life
◦ All important things happen at a surface!
Summary
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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.asp
SJSU Biomedical Materials Program
References