Techniques for Polymer Modification

1. Techniques for Polymer Modification Behzad Pourabbas Sahand University of Technology Tabriz-Iran pourabas@sut.ac.ir

2. 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. www.stocksurfaces.com. http://strangepaths.com/ http://plus.maths.org http://www.physik.uni-marburg.de http://www.physics.upenn.edu Surfaces to Ponder

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

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

12. CO2Phase Diagram http://www.chem.ufl.edu/~itl/2045/lectures/lec_f.html

13. Surface formation at different length scales: Diffusion Layers http://www.uni-regensburg.de/Fakultaeten/nat_Fak_I/Mat8/lst/spp/projectSPP1095solidification.html HeterogeneousSurface Structure

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

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

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

19. 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. • http://www.ksvinc.com/surface_tension.htm 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. http://www.sciencekids.co.nz/ http://hyperphysics.phy-astr.gsu.edu/ 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 http://www.ksvinc.com/LB.htm

24. 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

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

26. 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. Molecular adsorption to Surfaces? http://www.chem.qmul.ac.uk/surfaces/scc/

27. Physisorption • Physical bonds • Chemisorption • Chemical bonds • Self-Assembled Monolayers (SAMs) • Alkane thiols on solid gold surfaces • Self assembly of monolayers Adsorption / Self AssemblyProcesses on Surfaces

28. 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. Chemi / Physi - Adsorption http://www.chem.qmul.ac.uk/surfaces/scc/scat2_4.htm

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

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

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

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

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

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

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

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

39. 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

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

41. 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

42. 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. 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

44. 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

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

46. 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. • Intramolecularself-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 Molecular Self-Assembly

47. 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 Self Assembled Monolayers

48. A schematic of SAM (n-alkanethiolCH3(CH2)nSH molecules) formation on a Au(111) sample. The self-assembly process. An n-alkanethiol 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. http://www.dojindo.com/sam/SAM.html

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