Interactions, phase behavior and rheological properties of polymer-nanoparticle mixtures
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This research focuses on the interactions, phase behavior, structural characteristics and rheological properties of multicomponent polymer-particle mixtures. The systems considered in this study include spherical and rodlike particles in presence of non-adsorbing, adsorbing and grafted polymers. A hybrid multiscale approach is presented which implements polymer self consistent field theory in combination with the McMillan-Mayer framework to deduce the polymer-mediated interactions between the particles. The conformational characteristics of the polymers in the vicinity of particles are extracted within the mean field framework. A novel off-lattice simulation scheme is presented which combines the equilibrium interactions between the particles with the structural characteristics of polymers and allows for simultaneous identification of thermodynamic phase behavior, structure and rheological properties of polymer-particle mixtures. An accurate numerical solution of field theoretic equations is employed to discern the role of particle curvature in governing the equilibrium phase behavior, gelation transitions and rheological characteristics of such mixtures, with particular emphasis on the nanoparticle regime. For the case of non-adsorbing polymer, our results demonstrate significant multibody effects with profound consequences for the phase behavior of the particles. We have also analyzed the effect of surface saturation and particle curvature on the polymer adsorption characteristics to highlight differences in the structure of adsorbed polymer layers on nanoparticles from that on larger particles. These structural characteristics are utilized in particlebased simulations to quantify the phase behavior, percolation thresholds and elastic properties of polymer-nanoparticle systems and successfully rationalize experimental observations in context of polymer-nanoparticle mixtures. We also present a systematic study on the adsorption characteristics, the effective pair-interaction potentials and the resulting phase behavior, percolation transitions of nanorods dispersed in solutions of adsorbing polymers and discuss the efficacy of polymers in preventing van der Waals induced bundling of nanotubes. Finally, we study adsorption of model proteins on the surfaces carrying grafted polymer layers and delimit the physical parameters that control the resistance of surface grafted polymers to protein adsorption.