Monte Carlo Simulation On Configuration And Diffusion Of Polymer In Narrow Channels

Many theoretical researches and computer simulations have studied the dynamics of polymer confined in homogenous channels, namely, the interaction between polymer and channels does not change in the direction of the channels. However, in the real systems, polymer-channels interaction may vary along the channels direction as a result of the change of pH or unevenly distributed charges on channel surfaces, which would form complicated channels with complicated interactions. However we know little about how the polymer behaves, including polymer conformation and polymer dynamics, in complicated channels. It’s necessary to study configuration and diffusion of polymer in narrow channels.In this dissertation, we use Monte Carlo simulation to investigate the thermodynamics and dynamics of polymer in narrow cylindrical channels. We use bead-spring polymer model, a coarse-grained models of self-avoiding linear chain with long range attractions. We consider three different interactions:the interactions between bonded monomers, the interactions between non-bonded monomers, and monomer-channel interactions. Especially, the interaction between the polymer and the channels is Lennard-Jones potential. Three kinds of channels are taken into accounted:(1) a smooth channel where the monomer-channel interaction is independent of monomer position along the channel; (2) a periodic channel where the interaction is periodically change along the direction of the channel; and (3) a gradient channel where the interaction is gradiently changed with the position of monomer along the channel. Firstly, we examine the conformational properties of polymer in the smooth channel. A transition from a desorbed state to an adsorbed state occurs when monomer-channel interaction εpt equals 1.35 for polymer with length N= 32. Secondly, we find that diffusion coefficient can be influenced by a multiplicity of different factors in the subsequent studies, such as monomer-channel interaction, period length, and radius of channel. In the smooth channel, diffusion coefficient is independent of radius of channel and the monomer-channel interaction. But the diffusion coefficient is dependent on radius of channel and monomer-channel interaction in the periodic channels, because the existence of the periodic potential would against the polymer from trans location. Finally, we study the dynamics of the polymer in the gradient channel. The results show that the polymer can be driven to move in one direction by the gradient interaction. And both periodic potential and gradient potential will obviously influence the dynamics of polymer, indicating that there may be more than one physical mechanism could affect the behavior of polymer dynamics.