Computer Simulation Study On Stiffness Effects On Conformation And Dynamics Of Polymeric Chains

Soft matter physics is one of the hot topics in current international condensed matter physics. The study of soft matter is of great significance, not only because it pushes the basic research of condensed matter physics into a more sophisticated and colorful field, but because it has a very close relationship with our daily life and industry. Thus it has particularly important application prospects。In this article Weeks-Chander-Anderson (WCA) potential, bending potential and finitely extensible nonlinear elastic (FENE) potential are introduced into bead-spring model of polymer chains to model excluded volume interactions, chain stiffness and chain connection respectively. The dynamics of polymer chains in dilute good solutions is described by Langevin equation. Hence the effects of the chain stiffness on the structural and dynamical properties of polymer chains can be investigated. The main results of study are presented as:Firstly, the effects of the chain stiffness on scaling laws of root-mean-square end-to-end distance, rotational relaxation time and center-of-mass diffusion coefficient are investigated respectively. Simulations results show that with the increase of chain stiffness, scaling exponents of the three quantities almost don't change and are in quite satisfactory agreement with that of Rouse model, all three prefactors progressively increase, but the pace of increase gradually becomes slow, and they finally reach saturation, indicating that chain stiffness doesn't influence the conformation and dynamic scaling properties of polymer chains, but only changes microstructure of polymer chains.Secondly, the effects of the chain stiffness on bond auto-correlation function and the chain persistence length are discussed. Simulations results show with the increase of chain stiffness, the slopes of bond auto-correlation curves progressively become smaller, and after a certain level of chain stiffness, all curves almost coincide. Moreover, with the increase of chain stiffness, at first the chain persistence length increases rapidly, then a plateau domain appears, and persistence length corresponding to the plateau domain is consistent with predicted value of our model theory. These phenomena show that the increase of chain stiffness makes the correlation length and persistence length larger, but the effects of chain stiffness are limited, as they only change microstructure of polymer chains.Lastly, the effects of the chain stiffness on static structure factor and pair correlation function are considered. Simulations results show the increase of chain stiffness makes the probability of finding a monomer located between the first and second peaks or the second and third peaks smaller. And the scaling behavior of static structure factor is indeed changed from flexible chain characteristics to rod-like ones due to the increase of chain stiffness. Static structure factor and pair correlation function are two physical quantities which can be used to describe directly microstructure. By closely examining the two physical quantities, it is further confirmed that chain stiffness on microstructure of polymer chains does have a great impact.