Multi-scale Molecular Simulations On The Structure-Property Relationship Of Polymers

Polymer materials play fundamental roles in human’s daily life and research fileds suchas life science, chemistry and chemical engineering, foods, environments and pharmaceutics.Computer molecular simulations are useful tools to elucidate mechanisms of differentphenomena happened in polymer materials and ultimately to provide theoretical backgroundsto develop new materials.This work firstly employed grand canonical Monte Carlo and molecular dynamicssimulations to study oxygen sorption and diffusion in amorphous poly(lactic acid)(PLA) andPSiMA-IPN-PMPC hydrogel. At room temperature, amorphous PLA is glassy whilePSiMA-IPN-PMPC hydrogel is rubbery. Oxygen sorption in glassy PLA obeys the dual-modesorption model whereas oxygen sorption in rubbery hydrogel follows Henry’s law. It is foundthat water content has influence on oxygen sorption and diffusion in both materials. As watercontent in PLA is increased, oxygen’s sorption coefficient decreases whereas oxygen’sdiffusion coefficient firstly decreases and then increases. For PSiMA-IPN-PMPC hydrogel,the increase of water content will reduce both oxygen’s sorption and diffusion coefficients.In the investigation of structural and transport propeties of proton exchange membranesused for fuel cells, we utilized dissipative partilcle dynamics and molecular dynamicssimulations to study humidified Nafion membrane and Nafion-ionic liquid compositemembrane, respectively. For humidified Nafion membrane, we mainly studied effects ofwater content and poly(vinyl alcohol)/Nafion blend ratio on microstructures of Nafion. Whilefor Nafion-ionic liquid composite membrane, we mainly studied confinement effect of Nafionon ionic liquid structures and diffusion. It is found that formation mechanisms of waterclusters and ionic liquid clusters in Nafion are different. Tubular water clusters can be formedin Nafion, and all water clusters and enclosed by sulfonate groups. In Nafion-[bmim][BF4]composite membrane, pure ionic liquid clusters can be formed due to the presence of alkylchains on [bmim]+cations.Finally, coarse-grained molecular dynamics were used to study the self-assemblybehavior between PAMAM dendrimers and polyelectrolyte. It is found that PAMAMdendrimers can aggregate in water in a generation-controlled manner. Besides, PAMAMgeneration and PAMAM/polyelectrolyte charge ratio affect dendriplex formation.