Title: Elastic colloidal monopoles and reconfigurable self-assembly in liquid crystals

Abstract

Monopole-like electrostatic interactions are ubiquitous in condensed matter, but they are often screened by counter-ions and cannot be switched from attractive to repulsive. In colloidal science, where the main goal is to develop colloidal particles that mimic and exceed the diversity and length scales of atomic and molecular assembly, electrostatically charged particles cannot change the sign of their surface charge or transform from monopoles to higher-order multipoles. In liquid-crystal colloids, elastic interactions between particles arise to minimize the free energy associated with elastic distortions in the long-range alignment of rod-like molecules around the particles. In dipolar quadrupolar and hexadecapolar nematic colloids, the symmetries of such elastic distortions mimic both electrostatic multipoles and the outermost occupied electron shells of atoms. Electric and magnetic switching, spontaneous transformations and optical control of elastic multipoles, as well as their interactions with topological defects and surface boundary conditions, have been demonstrated in such colloids. However, it has long been understood that elastic monopoles should relax to uniform or higher-order multipole states because of the elastic torques that they induce. We develop nematic colloids with strong elastic monopole moments and with elastic torques balanced by the optical torques induced by ambient light. We demonstrate the monopole-to-quadrupolemore » reconfiguration of these colloidal particles by unstructured light, which resembles the driving of atoms between the ground state and various excited states. We show that the sign of the elastic monopoles can be switched, and that like-charged monopoles attract whereas oppositely charged ones repel, unlike in electrostatics. We also demonstrate the out-of-equilibrium dynamic assembly of these colloidal particles. This diverse and surprising behaviour is explained using a model that considers the balance of the optical and elastic torques that are responsible for the excited-state elastic monopoles and may lead to light-powered active-matter systems and self-assembled nanomachines.« less

Authors:

Yuan, Ye ^[1]; Liu, Qingkun ^[1]; Senyuk, Bohdan ^[1]; Smalyukh, Ivan I. ^[2]

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+ Show Author Affiliations

1. Univ. of Colorado, Boulder, CO (United States)
2. Univ. of Colorado, Boulder, CO (United States). Dept. of Electrical, Computer and Energy Engineering; Univ. of Colorado, Boulder, CO (United States). Soft Materials Research Center; National Renewable Energy Lab. (NREL), Golden, CO (United States). Renewable and Sustainable Energy Institute

Publication Date:

Wed May 29 00:00:00 EDT 2019

Research Org.:

Univ. of Colorado, Boulder, CO (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1580704

Grant/Contract Number:  

SC0019293

Resource Type:

Accepted Manuscript

Journal Name:

Nature (London)

Additional Journal Information:

Journal Name: Nature (London); Journal Volume: 570; Journal Issue: 7760; Journal ID: ISSN 0028-0836

Publisher:

Nature Publishing Group

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE