Analysis of interactions between finite-sized particles and terminally attached polymer using numerical self-consistent-field theory


Non-specific protein adsorption is known to influence many processes. For example, fouling of food processing equipment or fouling of biomedical implants often occurs because of strong protein adsorption. Protein adsorption on these and other surfaces, such as biomaterials, can however be reduced by attaching polymer chains by one end to the surface. Terminally attached polymer chains have also found application in size-based chromatographic separations. The goal of this thesis is to improve our understanding of the way in which solute molecules interact with terminally attached polymer chains, and to use this knowledge to predict optimum system conditions for minimizing protein adsorption. We develop a numerical selfconsistent- field lattice model, based on an earlier model of Scheutjens and Fleer [1979; 1980], to calculate theoretical results for the polymer density distribution of isolated and interacting chains around a solute particle positioned at a fixed distance from a surface. In addition, the excess energy required to move the particle into the polymer chains (interaction energy) is calculated using a statistical mechanical treatment of the lattice model. The effect of system variables such as particle size, chain length, surface density and interaction parameters on density distributions and interaction energies is also studied. The model is first applied to the compression of a single polymer chain by a disc of finite radius. Results are compared to predictions of a previous scaling thermodynamic model by Subramanian et al. [1995]. We see no first order partial-escape transition as reported by Subramanian et al. Instead, we find that the energy required to compress the chain increases monotonically, becoming independent of chain length at very close compression Calculations for the interaction of a solute particle with a surface covered by many polymer chains (a brush) shows that the polymer segments will fill in behind the particle quite rapidly as it moves toward the surface. When there is no strong energetic attraction between the polymer and solute we predict that the interaction energy will be purely repulsive upon compression due to losses in conformational entropy of the polymer chains. Above a critical chain length, which depends upon particle size, a maximum in the force required to move the particle toward the surface is observed due to an engulfment of the particle as chains attempt to access the free volume behind the particle. If an attraction exists between the polymer and solute, such that a minimum in the interaction energy is seen, the optimum conditions for solute repulsion occur at the highest surface density attainable. Long chain length can lead to increased solute concentration within the polymer layer due to the fact that more favourable polymer-solute contacts are able to occur than with short chains at a similar entropic penalty.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat

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