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application. For example, in the case of biocompatible materials it is important to obtain thermodynamic prevention of protein adsorption, since the biomaterial is expected to be in contact with the blood stream for long periods of time. However, in the case of drug carriers, control of the kinetics of adsorption is enough, since in this case one is interested in preventing protein adsorption on the time scale that the drug is delivered to the target cell. We will show our theoretical studies on both the kinetic and thermodynamic control of protein adsorption. Most of our studies are on model PEO molecules since these are the polymers that have been most extensively used experimentally. PEO is a water-soluble polymer that also has affinity for hydrophobic surfaces. Therefore, the structure of the polymer layer and thus, its ability to control protein adsorption depends upon the polymer-surface interactions. Overall we find that when the polymers are attracted to the surfaces the polymer layer is more effective for the thermodynamic control of protein adsorption than surfaces that do not attract the polymer. For the kinetic control the opposite is true. Namely, surfaces with polymers that are not attracted to them exert a stronger steric repulsion to approaching proteins than surfaces with attracting polymers. In all cases polymer surface coverage is the most important parameter to prevent protein adsorption. As the surface coverage increases, the ability of the polymer to prevent protein adsorption increases. At fixed polymer surface coverage, the equilibrium adsorption of proteins is independent of polymer molecular weight once the thickness of the brush is larger than the size of the protein. However, increasing chain length at fixed surface coverage results in an exponential increase of the time scale for adsorption. This is the result of the increased range and strength of the effective surface-protein interactions as polymer molecular weight increases. The kinetic process of protein adsorption on surfaces with grafted polymers will be shown to be rather complex. This is due to the fact that as proteins adsorb the polymer layer is deformed and therefore, the interactions that the proteins arriving from solution feel changes with time. The changes in the adsorption process due to the ability of the proteins to change their conformation upon adsorption will be described in detail as well as the effect of charges on the proteins, polymers and surfaces. References Most of the work presented in this talk appears in the following publications. 1. Szleifer, I., 1997. "Protein Adsorption on Surfaces with Grafted Polymers: A Theoretical Approach", Biophysical J. 72, 595-612. 2. Szleifer, I., 1997. “Protein Adsorption on Tethered Polymer Layers: Effect of Polymer Chain Architecture and Composition”, Physica A 244, 370-388. 3. Szleifer, I., 1997. “Polymers and Proteins: Interactions at Interfaces: Current Opinion in Solid State and Materials Science 2, 337-344. 4. McPherson, T., Kidane, A., Szleifer, I. and Park, K., 1998. “Prevention of Protein Adsorption by Tethered PEO Layers: Experiments and Single Chain Mean Field Analysis”. Langmuir 14, 176-186. 5. Satulovsky, J., Carignano, M.A. and Szleifer, I., 2000. “Kinetic and Thermodynamic Control of Protein Adsorption”. Proc. Nat. Acad. Sci. 97, 9037-9041. 6. Carignano M.A. and Szleifer, I., 2000. “Prevention of Protein Adsorption by Flexible and Rigid Chain Molecules”, Colloids and Surfaces B: Biointerfaces 18, 169-182. 7. Szleifer I. and Carignano, M.A., 2000. “Tethered Polymer Layers: Phase Transitions and Reduction of Protein Adsorption”. Feature Article in: Macromolecular Rapid Communications 21, 423-448. 8. Carignano M.A. and Szleifer, I., 2002. “Adsorption of Model Charged Proteins on Charged Surfaces with Grafted Polymers”. Mol. Phys. (in press). 9. Fang Fang and Szleifer, I., 2002. “Effect of Molecular Structure on the Adsorption of Protein on Surfaces with Grafted Polymers”. Langmuir 18, 5497-5510.
MODELLING STRUCTURE AND ADHESION AT POLYMER-POLYMER INTERFACES D.N. Theodorou School of Chemical Engineering, National Technical University of Athens, GR-15780 Athens, Greece and ICE/HT-FORTH, GR-26500 Patras, Greece email: doros@central.ntua.gr ABSTRACT Copolymers are remarkably effective in improving adhesion between immiscible polymers, or between polymers and solid substrates on which the polymer chains do not adsorb strongly. Predicting the molecular organisation and mechanical response upon deformation of polymer/polymer and polymer/solid interfaces strengthened with copolymers can serve as a basis for the “molecular engineering” design of materials with optimal interfacial properties. Using the work of Scheutjens and Fleer (Scheutjens 1979) as a starting point, we have developed a lattice-based self-consistent field (SCF) theory for capturing the molecular-level structure of interfaces formed by polymer melts in contact with other polymer melts or solid substrates, in the absence or presence of copolymers. Real polymer and copolymer chains are mapped onto the model representation invoked in the theory in a manner that respects their mass density in the homogeneous bulk, their contour length, and their conformational stiffness (characteristic ratio). The propagation of conformations is envisioned as a secondorder Markov process, involving an energetic penalty for chain bending. Interaction (χ) parameters between dissimilar segments, when needed, are obtained from fitting binary interfacial widths between the corresponding polymer melts. Application of the theory to interfaces between polystyrene (PS) and poly(methyl methacrylate) (PMMA) (Fischel 1995) in the presence of a symmetric PS-PMMA diblock copolymer gave segment density profiles in very favourable agreement with neutron reflectivity measurements (Russell 1991). The end-segment, mean square junction-to-end distance normal to the interface, shape parameter, and bond-order parameter profiles indicate that copolymer chains are significantly stretched under experimental conditions. For fixed surface density of the copolymer, with increasing block length, a broad transition from reflected random coil to “brush” behaviour occurs over the region where the block radii of gyration are 1.2 to 1.7 times the mean interchain spacing. At very high surface densities, the copolymer can no longer reside as a monolayer at the surface. Surface-phase equilibrium calculations predict that patches of trilayer will appear when the volume of copolymer per unit surface is roughly three times the block unperturbed root mean square radius of gyration. This predicted appearance of structures more complex than a monolayer at the surface is consistent with the emergence of off-specular scattering in neutron reflectivity measurements. It suggests an upper limit to the degree of mechanical strengthening of the interface by addition of larger amounts of block copolymer, as seen experimentally. Our SCF theory, in parallel with neutron reflectivity measurements, has been applied to probe interfaces between PS of molar mass 186 kg/mol and polished silicon wafer substrates (SiO2), in the presence of diblock copolymers of poly(2-vinyl pyridine) (PV2P) and PS as adhesion promoters (Retsos 2002). In these systems, prepared from the melt, the PV2P (“anchor”) block of the copolymer adsorbs strongly on the surface, while the “dangling” PS block mixes with the PS homopolymer. The molar mass of the dangling block, which was deuterated and therefore visible in the experiments, was kept constant at 75 kg/mol, while that of the anchor block was varied systematically between 3.4 and 102 kg/mol. The dangling block profile was found to exhibit a maximum, which decreases in height and moves away from the surface as the length of the anchor block is increased. Results from the SCF calculation are in very good agreement with the experiment. The anchoring block is not flat (pancakelike) as often assumed, but forms a layer of thickness
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Frontis - Wageningen International
Page 3 and 4: Prof. dr. Hans Fraaije Leiden Unive
Page 5 and 6: Prof. Ullrich Steiner University of
Page 7 and 8: Preface Self-consistent field model
Page 9 and 10: covered by polymers), and R. Rajago
Page 11 and 12: FIRST-ORDER WETTING TRANSITION AT F
Page 13 and 14: MOLECULAR SCF MODELLING OF PORES IN
Page 15 and 16: COLLAPSE OF POLYMER BRUSHES GRAFTED
Page 17 and 18: SURFACE FORCES, SUPRAMOLECULAR POLY
Page 19 and 20: SWEET BRUSHES: SYNTHESIS AND INTERF
Page 21 and 22: EFFECT OF MIXING OF TWO CHARGED PHO
Page 23 and 24: Figure 2 show a semi-log comparison
Page 25 and 26: MODELING OF STATIONARY POLYMER DIFF
Page 27 and 28: THEORY AND SIMULATION OF BILAYER ME
Page 29 and 30: Figure 1. Time evolution of the she
Page 31 and 32: SALT EFFECT TO RAYLEIGH DROPLETS OF
Page 33 and 34: MACROMOLECULES AT INTERFACES, A FLE
Page 35 and 36: APPLICATION OF HETEROGENEOUS LATTIC
Page 37 and 38: 8. Linse, P., 1993b. Phase behavior
Page 39 and 40: MODELING INTERFACIAL EFFECTS ON THE
Page 41 and 42: Using this patterned electrode, we
Page 43 and 44: span the gap between the electrodes
Page 45 and 46: desirable to use a probe with a muc
Page 47 and 48: span the gap between the electrodes
Page 49 and 50: MEMBRANE FUSION: RESULTS FROM SIMUL
Page 51 and 52: the transition temperature T * when
Page 53: PROTEIN ADSORPTION ON SURFACES WITH
Page 57 and 58: References 1. Fischel, L.B. and The
Page 59 and 60: MULTIDOMAIN CONFORMATIONS OF RANDOM
Page 61 and 62: SUPRAMOLECULAR COORDINATION POLYMER
Page 63 and 64: INFLUENCE OF POLYMERS ON THE BENDIN
Page 65 and 66: SPINODAL DECOMPOSITION IN BINARY PO
Page 67 and 68: PERSISTENCE LENGTH OF WORM-LIKE MIC
Page 69 and 70: For small particles with radius R <
Page 71: MEAN-FIELD THEORY FOR THE ADSORPTIO
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