Non-ideal behavior of intramolecular structure factor of dilute polymers in a theta solvent

TL;DR

This paper investigates the non-ideal intramolecular structure factor of dilute polymers in a theta solvent, revealing deviations from ideal chain behavior and similarities to melt states through Monte Carlo simulations and theoretical analysis.

Contribution

It provides the first detailed simulation and theoretical analysis of the intramolecular structure factor of polymers at the theta point, highlighting non-ideal features.

Findings

Distinct hump and dip in the structure factor at the theta point

Similarity of the structure factor features to polymer melts

First-order perturbation theory fits well, second virial coefficient remains non-zero

Abstract

We study the configurational properties of single polymers in a theta solvent by Monte Carlo simulation of the bond fluctuation model. The intramolecular structure factor at the theta point is found to be distinctively different from that of the ideal chain. The structure factor shows a hump around $q\sim 5/R_g$ and a dip around $q\sim 10/R_g$ in the Kratky plot with $R_g$ being the radius of gyration. This feature is apparently similar to that in a melt. The theoretical expression by the simple perturbation expansion to the first order in terms of the Mayer function can be fitted to the obtained structure factor quite well, but the second virial coefficient cannot be set to zero.