Breakdown of inverse morphologies in charged diblock copolymers

TL;DR

This study uses Brownian Dynamics simulations to explore how temperature and dielectric constant influence the morphology and dynamics of charged diblock copolymers, revealing significant effects of electrostatic interactions and medium polarity.

Contribution

It provides detailed insights into the morphological transitions of charged diblock copolymers under varying dielectric conditions, aligning simulation results with experimental and theoretical findings.

Findings

Low dielectric constant leads to ion-counterion multiplet formation affecting morphology.

High dielectric constant results in behavior similar to neutral polymers with long-range order.

Morphologies and swelling ratios are sensitive to medium polarity and electrostatic interactions.

Abstract

Brownian Dynamics simulations are carried out to understand the effect of temperature and dielectric constant of the medium on microphase separation of charged-neutral diblock copolymer systems. For different dielectric media, we focus on the effect of temperature on the morphology and dynamics of model charged diblock copolymers. In this study we examine in detail a system of partially charged block copolymer consisting of 75% neutral blocks and 25% of charged blocks with 50% degree of ionization. Our investigations show that due to the presence of strong electrostatic interactions between the charged block and counterions, the block copolymer morphologies are rather different than their neutral counterpart at low dielectric constant, however at high dielectric constant the neutral diblock behaviors are observed. This article highlights the effect of dielectric constant of two different media on different thermodynamic and dynamic quantities. At low dielectric, the morphologies are a direct outcome of the ion-counterion multiplet formation. At high dielectric, these charged diblocks behavior resembles that of neutral and weakly charged polymers with sustainable long-range order. Similar behavior has been observed in chain swelling, albeit with small changes in swelling ratio for large change in polarity of the medium. The results of our simulations agree with recent experimental results and are consistent with recent theoretical predictions of counterion adsorption on flexible polyelectrolytes.