Programmable self-assembly of core-shell ellipsoids at liquid interfaces

TL;DR

This paper demonstrates how adding a soft shell to ellipsoidal particles at liquid interfaces enables control over their self-assembly configurations, transitioning between tip-to-tip and side-to-side arrangements based on aspect ratio and shell properties.

Contribution

It introduces a method to program the self-assembly of core-shell ellipsoids at liquid interfaces, combining experiments, theory, and simulations to predict and control their assembly structures.

Findings

Pure ellipsoids form chain-like assemblies regardless of aspect ratio.

Core-shell ellipsoids switch from flower-like to chain-like structures as aspect ratio increases.

Phase diagram maps assembly preferences based on aspect ratio and shell-to-core ratio.

Abstract

Ellipsoidal particles confined at liquid interfaces exhibit complex self-assembly behaviour due to quadrupolar capillary interactions induced by meniscus deformation. These interactions cause particles to attract each other in either tip-to-tip or side-to-side configurations. However, controlling their interfacial self-assembly is challenging because it is difficult to predict which of these two states will be preferred. In this study, we demonstrate that introducing a soft shell around hard ellipsoidal particles provides a means to control the self-assembly process, allowing us to switch the preferred configuration between these states. We study their interfacial self-assembly and find that pure ellipsoids without a shell consistently form a "chain-like" side-to-side assembly, regardless of aspect ratio. In contrast, core-shell ellipsoids transition from "flower-like" tip-to-tip to "chain-like" side-to-side arrangements as their aspect ratios increase. The critical aspect ratio for transitioning between these structures increases with shell-to-core ratios. Our experimental findings are corroborated by theoretical calculations and Monte Carlo simulations, which map out the phase diagram of thermodynamically preferred self-assembly structures for core-shell ellipsoids as a function of aspect ratio and shell-to-core ratios. This study shows how to program the self-assembly of anisotropic particles by tuning their physicochemical properties, allowing the deterministic realization of distinct structural configurations.