Computer simulations of polymeric systems

This document contains two projects that use computer simulations as a powerful research tool to study polymeric systems. The first project is to study the crystallization of polymer melts in the presence of nanoparticles. Experimental results show that the presence of nanoparticles enhances the crystallization of polymer melts whether the interaction between particles and polymers is attractive or repulsive. The results imply that the effect of particles on the crystallization of polymer melts is entropic. Molecular dynamics simulations with a coarse-grained model were performed to investigate the mechanism of the enhancement. My simulation results show that the presence of particles locally induces the ordering of polymers in the melt state and modifies the free energy landscape of the system. As a result, it promotes the crystallization of polymer melts. My findings are consistent with experimental observations which indicate the entropic effect of the included particles.;In the second project, I study the effective interactions in poloxamer-lipid mixture at the air/water interface and try to understand the sealing mechanism of poloxamers to the damaged cell membrane. After a careful analysis of the systems under study, we proposed a simple model to describe them. Extensive Monte Carlo simulations were performed. My simulation results agree well with experimental observations, namely, the adsorption of poloxamers onto the air/water interface induces large amount of lateral pressure jump and crystal-like clusters of lipids formed and corralled by poloxamers. The compression of the interface will squeeze out poloxamers, and the structure of lipid clusters remains and the cluster size increases. My results also show that the driving force for the cluster formation of lipids and the corralling effect of poloxamers to lipids are the size mismatch between lipids and poloxamers and the soft long-range repulsion between poloxamers. These two conditions are necessary for the observations. Because our model is generic, our finding can provide a guideline for how to form high-ordered clusters of nanoparticles in two dimensions.