Design of linear block copolymers and ABC star terpolymers that produce two length scales at phase separation

TL;DR

This paper proposes design criteria for block copolymers to naturally form quasicrystals with two specific length scales at phase separation, using the Random Phase Approximation to identify suitable parameters.

Contribution

It introduces a theoretical framework for designing block copolymers that favor quasicrystal formation by achieving specific length scale ratios.

Findings

Identified parameter windows with length scale ratio of 1.93 in block copolymer models.

Demonstrated that simple, synthesizable copolymer models can produce quasicrystal-friendly length scales.

Provided design criteria applicable to linear and star-shaped copolymer systems.

Abstract

Quasicrystals (materials with long range order but without the usual spatial periodicity of crystals) were discovered in several soft matter systems in the last twenty years. The stability of quasicrystals has been attributed to the presence of two prominent length scales in a specific ratio, which is 1.93 for the twelve-fold quasicrystals most commonly found in soft matter. We propose design criteria for block copolymers such that quasicrystal-friendly length scales emerge at the point of phase separation from a melt, basing our calculations on the Random Phase Approximation. We consider two block copolymer families: linear chains containing two different monomer types in blocks of different lengths, and ABC star terpolymers. In all examples, we are able to identify parameter windows with the two length scales having a ratio of 1.93. The models that we consider that are simplest for polymer synthesis are, first, a monodisperse A_L B A_S B melt and, second, a model based on random reactions from a mixture of A_L, A_S and B chains: both feature the length scale ratio of 1.93 and should be relatively easy to synthesise.