Spatially localized self-assembly driven by electrically charged phase separation

TL;DR

This paper investigates the formation of spatially localized self-assembled structures driven by phase separation and Coulombic interactions, extending classical models to include asymmetries, and analyzes their stability and patterns in one and two dimensions.

Contribution

It introduces an extended Ohta-Kawasaki model incorporating asymmetries and studies localized states and their stability, providing insights for nano-scale self-assembly control.

Findings

Multiple localized solutions in 1D form homoclinic snaking structures.

Distinct instability mechanisms for localized stripes in 2D.

Implications for designing low-cost nano electronic patterns.

Abstract

Self-assembly driven by phase separation coupled to Coulombic interactions is fundamental to a wide range of applications, examples of which include soft matter lithography via di-block copolymers, membrane design using polyelectrolytes, and renewable energy applications based on complex nano-materials, such as ionic liquids. The most common mean field framework for these problems is the non-local Cahn-Hilliard (a.k.a. Ohta-Kawasaki) framework. In this work, we study the emergence of spatially localized states in both the classical and the extended Ohta-Kawasaki model. The latter also accounts for: (i) asymmetries in long-range Coulomb interactions that are manifested by differences in the dielectric response, and (ii) asymmetric short-range interactions that correspond to differences in the chemical potential between two materials phases. It is shown that in one space dimension (1D) there is a multiplicity of coexisting localized solutions, which organize in the homoclinic snaking structure, bearing similarity to dissipative systems. In addition, an analysis of 2D extension is performed and distinct instability mechanisms (related to extended and localized modes) of localized stripes are discussed with respect to model parameters and domain size. Finally, implications to localized hexagonal patterns are also made. The insights provide an efficient mechanistic framework to design and control localized self-assembly that might be a plausible strategy for low cost of nano electronic applications, i.e., a rather simple nano scale fabrication of isolated morphologies.