Colloidal interactions and unusual crystallization versus de-mixing of elastic multipoles formed by gold mesoflowers

Ye Yuan,Mykola Tasinkevych,Ivan I Smalyukh

doi:10.1038/s41467-019-14031-2

Abstract

Colloidal interactions in nematic liquid crystals can be described as interactions between elastic multipoles that depend on particle shape, topology, chirality, boundary conditions and induced topological defects. Here, we describe a nematic colloidal system consisting of mesostructures of gold capable of inducing elastic multipoles of different order. Elastic monopoles are formed by relatively large asymmetric mesoflower particles, for which gravity and elastic torque balancing yields monopole-type interactions. High-order multipoles are instead formed by smaller mesoflowers with a myriad of shapes corresponding to multipoles of different orders, consistent with our computer simulations based on free energy minimization. We reveal unexpected many-body interactions in this colloidal system, ranging from de-mixing of elastic monopoles to a zoo of unusual colloidal crystals formed by high-order multipoles like hexadecapoles. Our findings show that gold mesoflowers may serve as a designer toolkit for engineering colloidal interaction and self-assembly, potentially exceeding that in atomic and molecular systems.

Highlights

Colloidal interactions in nematic liquid crystals can be described as interactions between elastic multipoles that depend on particle shape, topology, chirality, boundary conditions and induced topological defects
We reveal changes in physical behavior like pair interactions of colloidal particles stemming from small changes in particle dimensions and shapes, as exemplified by the mesoflower nematic colloidal system
The cetyltrimethylammonium bromide (CTAB) coating on the surface of the particles sets perpendicular boundary conditions for the director n(r), while the sharp spikes sticking out in all directions perturb the uniform far-field alignment n0 of the liquid crystal (LC) defined by the rubbing direction of the confining substrates

Summary

Introduction

Colloidal interactions in nematic liquid crystals can be described as interactions between elastic multipoles that depend on particle shape, topology, chirality, boundary conditions and induced topological defects. Colloidal spheres can induce elastic dipoles[3], quadrupoles[12], or hexadecapoles[17] depending on whether singular point[3] or “Saturn ring” disclination loop[32,33] or simultaneously both types of defects[17] are formed, respectively Such ability of achieving different types of elastic multipoles by colloidal inclusions of the same type is limited, limiting the diversity of assemblies and composite materials that can be achieved. These mesoflowers are mesostructures of gold with highly diverse shapes and with characteristic sharp spikes of sub-micron dimensions[34] These complex yet diverse particles allow for inducing different elastic multipoles when dispersed in a nematic LC, which for small particles range from dipoles to hexadecapoles, and even higher order multipoles. In the spirit of the colloidal atom paradigm, our findings reveal that LC colloids have a great potential of expanding the length scales of self-assembly from atomic to colloidal scales[1,2,3], and diversifying the forms of colloidal organization by going beyond what is accessible to atomic systems

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Results

Conclusion