Phase Diagrams Of Diblock Copolymersin Electric Field:A Self-consistent Field Theory Study

A distinct property of diblock copolymers is their ability to self-assemble ordered nanostructures,which can be conveniently tuned on the basis of the ratio and interaction between blocks.The spontaneous formation of ordered nanostructures in diblock copolymers has been extensively investigated because of their potential technological applications.We investigated the phase diagrams of diblock copolymers in external electrostatic fields by using real-space self-consistent field theory.The lamella,cylinder,sphere,and ellipsoid structures were observed and analyzed by their segment distributions,which were arranged to two types of phase diagrams to examine the phase behavior in weak and strong electric fields.One type was constructed on the basis of Flory-Huggins interaction parameter and volume fraction.We identified an ellipsoid structure with a body-centered cuboid arrangement as a stablephase and discussed the shift of phase boundaries in the electric fields.The other type of phase diagrams was established on the basis of the dielectric constants of two blocks in the electric fields.We then determined the regions of ellipsoid phase in the phase diagrams to examine the influence of dielectric constants on the phase transition between ellipsoidal and hexagonally packed cylinder phases.Furthermore,the eccentricity of ellipsoid was investigated by varying the dielectric constants of the two blocks,and the factors that affect the critical values of electric field strengths were also considered for the sphere-cylinder transitions in the electric fields with orientation [001].Finally,we investigated the critical strength of electric field with respect to the defect degree of electric field.A general agreement was obtained by comparing our results with those described in previous experimental and theoretical studies.