1. Techniques for Polymer Modification
Behzad Pourabbas
Sahand University of Technology
Tabriz-Iran

2. Syllabuses 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

3. You will have a CD full of Electronic Resourses
References

4. Surfaces and Interfaces
Behzad Pourabbas
Sahand University of Technology
Tabriz-Iran

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

6. Surfaces to Ponder www.stocksurfaces.com. http://strangepaths.com/
Surfaces to Ponder

7. Overview Importance of surfaces What is a surface? Surface structure
Surface processes
Surface interfaces
Surfaces in nature
Measuring surfaces
Modifying surfaces
Overview

8. Importance of Surfaces
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

9. 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 Defined

10. 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
Surfaces and Phases

11. Water Phase Diagram

12. CO2 Phase Diagram

13. Heterogeneous Surface Structure
Surface formation at different length scales:
Diffusion Layers

14. Real Surfaces Explained
Interfaces: Discontinuities
Bonds: Dangling bonds, attractive / repulsive forces, unit cell cleavage planes
Electron scattering: Surfaces can scatter electrons
Failure starts on the surfaces:
Cracks have surfaces: cohesive / adhesive failures
Real Surfaces Explained

15. 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.

17. 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).

18. Surface Processes Passivation Reconstruction
Oxide formation
Adventitious carbon
Reconstruction
Crystalline
Polymer orientation
Adsorption of gases and water vapor
Both can lead to surface passivation
Surface Processes

19. Surface Free Energy 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

20. 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.
Surface Free Energy

21. The unfavorable contribution to the total (surface) free energy may be minimized in several ways:
By reducing the amount of surface area exposed – this is most common / fastest
By predominantly exposing surface planes which have a low surface free energy
By altering the local surface atomic geometry in a way which reduces the surface free energy
Surface Energetics

22. Surface Tension http://www.sciencekids.co.nz/
Surface Tension

23. 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.
Surface Tension

24. The storage of energy at the surface of liquids
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

25. Surface Tension in Action

26. 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.

27. 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

28. 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.

29. 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 (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.

30. 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

31. 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)

32. 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.

33. ~99% of living organisms live in the top 1cm of the ocean
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
Surface Interfaces

34. Forces at Interfaces 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

35. Importance of Interfaces
Chemical reactions occur at interfaces
Particularly corrosion
Scattering energy
Electrons
Light
Phonons
An interface is actually two surfaces
Importance of Interfaces

36. Defects at Interfaces Missing atoms Extra atoms Dangling bonds
Defects and holes
Extra atoms
Surface segregation
Dangling bonds
Disrupted electronic properties
Dimensional issues
Lattice mismatch / shelves
Defects at Interfaces

37. Cohesive Failure Material A Material B
Material fails cohesively within B
Material B
Cohesive Failure

38. Adhesive Failure Material A Material fails adhesively between A and B
Material B
Adhesive Failure

39. 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.
Adhesive Failure (Craze)

40. Surface Reactions Oxidation Surface diffusion Diffusion and oxidation
Adventitious carbon bonding
Hydrocarbons from the atmosphere
Surface rearrangement
Polymers may reorient to minimize energy
Surface Reactions

41. A Typical Surface Hydrocarbons and water rapidly adsorb to a metal or
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 15
To 20 Angstroms, and hydrocarbons to a similar thickness.
This is part of the normal surface passivation process.
A Typical Surface

42. Langmuir-Blodgett Films
Definition of LB films
History and development
Construction with LB films
Building simple LB SAMs
Nano applications of LB films
Surface derivatized nanoparticles
Functionalized coatings in LB films
Langmuir-Blodgett Films

43. 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 "
Langmuir-Blodgett Films

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

45. 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.
Self Assembly

46. 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.

47. Self Assembled Monolayers
SAMs – Self Assembled Monolayers
Alkane Thiol complexes on gold
C10 or longer, functionalized end groups
Can build multilayer / complex structures
Used for creating biosensors
Link bioactive molecules into a scaffold
The first cells on earth formed from SAMs

48. The Self-Assembly Process
A schematic of SAM (n-alkanethiol 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

49. 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.

50. SAM Surface Derivatization
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.

51. SAMs C10 Imaging with AFM

52. Multilayer LB Film Process
Smart Materials for Biosensing Devices – Cell Mimicking Supramolecular Assemblies and Colorimetric Detection of Pathogenic Agents

53. Surface Contamination
All surfaces become contaminated!
It is a form of ‘passivation’
Oxidation of metals
Adventitious hydrocarbons
Chemisorption of ions
It can happen very rapidly
And be very difficult to remove
Surface Contamination

54. Measuring Surfaces 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
Measuring Surfaces

55. XPS/AES Analysis Volume

56. Surface Analysis Tools
SSX-100 ESCA on the left, Auger Spectrometer on the right

57. 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

58. 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 Treatments

59. Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

60. Surface Treatment of NiTi
Biomedical Devices and Biomedical Implants – SJSU Guna Selvaduray

61. 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

62. 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

63. 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

64. 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

65. Snow Cleaning with CO2

66. Surfaces in Nature Cell membranes Skin (ectoderm) Lungs
Self-assembled phospholipid bilayers
Proteins add functionality to the membrane
Skin (ectoderm)
Lungs
Exchange of O2, CO2, and water vapor
Cell surface recognition (m-proteins)
Major histocompatibility complex
Surfaces in Nature

67. Molecular Self Assembly
3D diagram of a lipid bilayer membrane - water molecules not represented for clarity
Different lipid model
top : multi-particles lipid molecule
bottom: single-particle lipid molecule

68. Cell Membranes

69. Summary 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

70. References http://www.eaglabs.com/ http://www.ksvinc.com/LB.htm
SJSU Biomedical Materials Program
References