Interfacial Phenomena of Solvent-diluted Block Copolymers

TL;DR

This paper develops a mean-field model to study the interfacial phenomena and phase behavior of solvent-diluted block copolymers, revealing how solvent interactions influence phase separation, interface deformation, and droplet morphology.

Contribution

It introduces a phenomenological mean-field approach to analyze solvent effects on block copolymer phases and interfaces, aligning with experimental and previous theoretical findings.

Findings

Critical point depends on solvent density.

Interface deformation occurs due to patterned substrates.

Surface tension varies non-monotonically with temperature.

Abstract

A phenomenological mean-field theory is used to investigate the properties of solvent-diluted di-block copolymers (BCP), in which the two BCP components (A and B) form a variety of phases that are diluted by a solvent (S). Using this approach, we model mixtures of di-block copolymers and a solvent and obtained the corresponding critical behavior. In the low solvent limit, we find how the critical point depends on the solvent density. Due to the non-linear nature of the coupling between the A/B and BCP/solvent concentrations, the A/B modulation induces modulations in the polymer-solvent relative concentration with a double wavenumber. The free boundary separating the polymer-rich phase from the solvent-rich one is studied in two situations. First, we show how the presence of a chemically patterned substrate leads to deformations of the BCP film/solvent interface, creation of terraces in lamellar BCP film and even formation of multi-domain droplets as induced by the patterned substrate. Our results are in agreement with previous self-consistent field theory calculations. Second, we compare the surface tension between parallel lamellae coexisting with a solvent phase with that of a perpendicular one, and show that the surface tension has a non-monotonic dependence on temperature. The anisotropic surface tension can lead to deformation of spherical BCP droplets into lens-shaped ones, together with re-orientation of the lamellae inside the droplet during the polymer/solvent phase separation process in agreement with experiment.