Fluctuations in Symmetric Diblock Copolymers: Testing A Recent Theory

TL;DR

This study uses Monte Carlo simulations to evaluate the accuracy of three theories describing composition fluctuations in symmetric diblock copolymer melts, finding the newer ROL theory to be broadly applicable.

Contribution

It tests and compares the predictive accuracy of RPA, FH, and ROL theories against simulation data for symmetric diblock copolymers.

Findings

ROL theory is accurate over a wide range of parameters.

FH theory is limited near the order-disorder transition.

RPA provides a baseline approximation.

Abstract

Composition fluctuations in disordered melts of symmetric diblock copolymers are studied by Monte Carlo simulation over a range of chain lengths and interaction strengths. Results are used to test three theories: (1) the random phase approximation (RPA), (2) the Fredrickson-Helfand (FH) theory, which was designed to describe large fluctuations near an order-disorder transition (ODT), and (3) a more recent renormalized one-loop (ROL) theory, which reduces to FH theory near the ODT, but which is found to be accurate over a much wider range of parameters.