Role of attractive force on the behavior of a polymer chain in solution

Abstract

We have investigated the behavior of a polymer chain in solution by molecular dynamics (MD) technique. For this purpose, the polymer was represented by a semirigid chain having a fixed bond length and bond angle with allowance for a hindered internal rotation. Interaction potentials for solvent-solvent (SS), chain-solvent (CS), and chain-chain (CC) particles were chosen to be an exp-6 potential form, with a provision that the CC-potential acts only between non-nearest neighbor particle pairs. Effect of the attractive interactions on physical properties of the polymer was investigated by comparing the results based on the exp-6 potentials with those based on a "shifted" exp-6 potential which includes only the repulsive part of the exp-6 potential. The present work includes the calculations on the equilibrium quantities such as the SS-, CS-, and CC-pair correlation functions, the mean square end-to-end distance, the mean square radius of gyration, and the eigenvalues of the moment of inertia tensor as well as the dynamic properties such as the autocorrelation functions for the mean square end-to-end distance and the mean square radius of gyration. The calculations show that the polymer configuration depends sensitively not only on the repulsive interaction but also on the attractive interaction. Namely, omitting the attractive term makes the polymer more compact making the gauche conformations more favorable over trans-conformations. The attractive interaction also produces the autocorrelation functions which decay slower than those for the pure repulsive potential.