Liquid crystalline structures formed by sphere-rod amphiphilic molecules in solvents

TL;DR

This study investigates how sphere-rod amphiphilic molecules self-assemble into various liquid crystalline structures in mixed solvents, revealing solvent-dependent formation of spherical and layered arrangements with potential applications in material science.

Contribution

It demonstrates the solvent-controlled self-assembly of sphere-rod molecules into diverse liquid crystalline structures, including spherical and layered formations, with detailed microscopy analysis.

Findings

Spherical structures filled with smectic-like layers observed via TEM.

Layered structures form at specific dioxane volume fractions, resembling smectic A liquid crystals.

Evaporation leads to birefringent nematic-like phases.

Abstract

Self-assembly of amphiphilic molecules is an important phenomenon attracting a broad range of research. In this work, we study the self-assembly of KTOF4 sphere-rod amphiphilic molecules in mixed water-dioxane solvents. The molecules are of a T-shaped geometry, comprised of a hydrophilic spherical Keggin-type cluster attached by a flexible bridge to the center of a hydrophobic rod-like oligodialkylfluorene (OF), which consists of four OF units. Transmission electron microscopy (TEM) uncovers self-assembled spherical structures of KTOF4 in dilute solutions. These spheres are filled with smectic-like layers of KTOF4 separated by layers of the solution. There are two types of layer packings: (i) concentric spheres and (ii) flat layers. The concentric spheres form when the dioxane volume fraction in the solution is 35-50 vol%. The flat layers are formed when the dioxane volume fraction is either below (20 and 30 vol%.) or above (55 and 60 vol%.) the indicated range. The layered structures show no in-plane orientational order and thus resemble thermotropic smectic A liquid crystals and their lyotropic analogs. The layered packings reveal edge and screw dislocations. Evaporation of the solvent produces a bulk birefringent liquid crystal phase with textures resembling the ones of uniaxial nematic liquid crystals. These findings demonstrate that sphere-rod molecules produce a variety of self-assembled structures that are controlled by the solvent properties.