Phase transition of a single star polymer: a Wang-Landau sampling study

TL;DR

This study uses Wang-Landau sampling to analyze the thermodynamic phase transitions of a single star polymer, revealing how arm density influences coil-globule and liquid-crystal transitions.

Contribution

It introduces a new shape factor method for efficiently identifying phase transitions in star polymers, and compares their behavior to linear polymers.

Findings

LC transition follows the same scaling law as linear polymers.

Increasing arm density shifts the coil-globule transition towards the LC transition.

Structural differences affect only the coil-globule transition, not the LC transition.

Abstract

Star polymer is a typical nonlinear macromolecule possessing special thermodynamic behaviors for the existence of a jointing point. The thermodynamic transitions of a single star polymer are systematically studied with bond fluctuation model using Wang-Landau sampling technique. A new analysis method applying the shape factor is proposed to determine coil-globule (CG) and liquid-crystal (LC) transitions, which shows higher efficiency and precision than canonical specific heat function. It is found that the LC transition of star polymer at lower temperature obeys the identical scaling law as linear polymer. With the increase of the arm density of star polymer, however, the CG transition point, corresponding to {\theta} temperature, shifts towards the LC transition and the reason comes from the high density arms of star polymer, which requires the lower temperature for attracting force to overcome the volume excluding effects of chain. This work clearly demonstrates that the distinction of linear and star polymers in structures only affects CG transition and has no influence on LC transition.