Fluctuation effects in the theory of microphase separation of diblock copolymers in the presence of an electric field

TL;DR

This paper extends the Fredrickson-Helfand theory to include electric field effects on diblock copolymer microphase separation, showing that electric fields suppress fluctuations and alter transition behavior.

Contribution

It introduces a generalized theory accounting for electric fields, predicting suppression of fluctuations and shifts in transition temperatures in diblock copolymer melts.

Findings

Electric fields suppress composition fluctuations.

Electric fields weaken the first-order transition.

The structure factor becomes anisotropic under an electric field.

Abstract

We generalize the Fredrickson-Helfand theory of the microphase separation in symmetric diblock copolymer melts by taking into account the influence of a time-independent homogeneous electric field on the composition fluctuations within the self-consistent Hartree approximation. We predict that electric fields suppress composition fluctuations, and consequently weaken the first-order transition. In the presence of an electric field the critical temperature of the order-disorder transition is shifted towards its mean-field value. The collective structure factor in the disordered phase becomes anisotropic in the presence of the electric field. Fluctuational modulations of the order parameter along the field direction are strongest suppressed. The latter is in accordance with the parallel orientation of the lamellae in the ordered state.