Orienting Ion-Containing Block Copolymers Using AC Electric Field

TL;DR

This paper investigates how ions influence the orientation of block copolymers under AC electric fields, revealing that ion presence and mobility contrast can significantly enhance alignment, especially at low frequencies.

Contribution

It introduces a theoretical framework showing ions can improve copolymer orientation and differentiate chain lengths, even without dielectric contrast.

Findings

Ion presence markedly increases alignment effects.

Orientation can occur without dielectric contrast if mobility contrast exists.

Ions enable orientation at low field frequencies and help distinguish polymer chain lengths.

Abstract

We consider orientation mechanisms for block copolymers in an electric field. Theoretical and experimental studies have shown that nonuniformity of the dielectric constant gives rise to a preferred orientation of the melt with respect to the applied field. We show that the presence of ions, as found in anionically prepared copolymers, may increase the alignment effect markedly. Time-varying (ac) and static (dc) fields are considered within a unified framework. We find that orientation of block copolymers can in principle be achieved without a dielectric contrast if there is a mobility contrast. The presence of ions is especially important at small field frequencies, as is in most experiments. Unlike the no-ions case, it is found that orienting forces depend on the polymer chain lengths. The mobile-ions mechanism suggested here can be used to reduce the magnitude of orienting fields as well as to discriminate between block copolymers of different lengths.