Micelle formation, gelation and phase separation of amphiphilic multiblock copolymers

TL;DR

This study uses lattice Monte Carlo simulations to explore how amphiphilic multiblock copolymers self-assemble into micelles, gels, and phase-separated structures depending on concentration, solvent quality, and monomer ratio.

Contribution

It provides a detailed phase diagram and identifies distinct structural regimes, including micelle formation, tubular structures, and gel networks, based on substitution levels and concentration.

Findings

Micelle formation depends on hydrophilic/hydrophobic ratio and concentration.

Gelation occurs via different mechanisms for poorly and highly substituted copolymers.

Phase diagram reveals sol-gel and inverse gel-sol transitions with changing interaction energy.

Abstract

The phase behaviour of amphiphilic multiblock copolymers with a large number of blocks in semidilute solutions is studied by lattice Monte Carlo simulations. The influence on the resulting structures of the concentration, the solvent quality and the ratio of hydrophobic to hydrophilic monomers in the chains has been assessed explicitely. Several distinct regimes are put in evidence. For poorly substituted (mainly hydrophilic) copolymers formation of micelles is observed, either isolated or connected by the hydrophilic moieties, depending on concentration and chain length. For more highly substituted chains larger tubular hydrophobic structures appear which, at higher concentration, join to form extended hydrophobic cores. For both substitution ratios gelation is observed, but with a very different gel network structure. For the poorly substituted chains the gel consists of micelles cross-linked by hydrophilic blocks whereas for the highly substituted copolymers the extended hydrophobic cores form the gelling network. The interplay between gelation and phase separation clearly appears in the phase diagram. In particular, for poorly substituted copolymers and in a narrow concentration range, we observe a sol-gel transition followed by an inverse gel-sol transition when increasing the interaction energy. The simulation results are discussed in the context of the experimentally observed phase properties of methylcellulose, a hydrophobically substituted polysaccharide.