Lipid islands on liquid crystal shells

Jan P F Lagerwall,Anjali Sharma,Giusy Scalia,Deepak Gupta

doi:10.1103/physrevresearch.4.013130

Abstract

By inducing phase separation in lipid monolayers on liquid crystal (LC) shells---thin hollow spheres of LC with water inside and outside---we reveal a rich set of coupled two- and three-dimensional (2D and 3D) self-organization phenomena enabled by the dual closely spaced internal and external spherical LC-water interfaces. Spindle-shaped 2D islands of condensed lipid monolayer first form at the primary interface where lipids are deposited, later also at the initially unexposed secondary interface, because lipids transfer through the LC. The LCs' elastic response to the 3D deformation caused by islands moves them from thin to thick regions on the shell and creates an attraction between opposite-side islands, topologically separated by the LCs, until they stack in a sandwich-like manner. We propose that the phase separation may be used for studying liposome adsorption on soft hydrophobic substrates, and to create unconventional colloidal particles with programmed interactions.

Highlights

Liquid crystals (LCs) brought into spherical geometry in droplets or shells are powerful model systems for studying the effects of confinement and topological constraints on the fluid long-range orientational order that is the hallmark of liquid crystal (LC) [1,2]
This gives rise to no visible consequence on the LC shells in our experiments [Fig. 1(d)] but after some tens of minutes, polarizing optical microscopy (POM) reveals small spindle-shaped islands with two cusps; see Fig. 1(e)
These islands, which rapidly grow in size and number during the continued experiment [Figs. 1(f)–1(h)], indicate that 2D phase separation by nucleation and growth, similar to what was observed by the Abbott group at a flat LC-aqueous interface [7], is taking place on our LC shells

Summary

Introduction

Liquid crystals (LCs) brought into spherical geometry in droplets or shells are powerful model systems for studying the effects of confinement and topological constraints on the fluid long-range orientational order that is the hallmark of LCs [1,2]. With the distance between these interfaces on the order of d ≈ 1 μm, increasing continuously from top to bottom or vice versa due to density mismatch between the LC and the inner droplet, shells have ideal geometry and scale for studying the unique competition between interfacial and bulk aspects of LC self-organization. The former is quantified by the anchoring strength W , describing how strongly the director n (the principle symmetry axis of the nematic phase) is controlled by the boundary conditions. A significant anchoring-induced deformation of n(r) is allowed only if d > K/W ≈ 1 μm [3]

Methods

Results

Conclusion