Date of Award

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Ivan I. Smalyukh

Second Advisor

Noel Clark

Third Advisor

Jao Van de Lagemaat

Fourth Advisor

David M. Walba

Fifth Advisor

Christopher Bowman

Abstract

Liquid crystals (LCs) have fascinating optical, mechanical and electrical properties that are intrinsically anisotropic. The relatively weak interactions between their constituting particles allows for manipulating these properties with low energy input, making them good candidates for engineering novel materials. In this work, we introduce colloidal particles of different material, shape, and surface functionalization into LCs and investigate a variety of colloidal interactions and dynamics mediated by LC director distortion. Firstly, noble metal nanoparticles of different shape and topology are synthesized re-dispersed in LC. Facile electric switching of these composites is reminiscent of that of pristine liquid crystals, but provides a means of reconfiguring the nanoparticle assembly and thus also the ensuing composite medium’s plasmonic properties. In addition to using particle shape and topology to guide the self-assembly process in LC, our study also extends to discovering the role of chirality of colloidal inclusions in affecting these long-range interactions, where chiral springs and helices are fabricated using two-photon photopolymerization. Our study shows that chirality may be a potential tool to modulate the global orientated self-organization of liquid crystal colloids. Surface functionalization is also a concern: photo-responsive molecules on the surface of colloidal particles further alters the interplay between LC directors and colloidal inclusions. We design and fabricate a micromotor system in LC consisting of silica micro-platelets capped with azobenzene monolayer that are sensitive to polarized blue light. Combined, these result in a feedback mechanism that spontaneously yields a continuous opto-elastic cycle and drives unidirectional particle spinning, with the handedness and frequency robustly controlled by the polarization and intensity of the incident light. Finally, the same mechanism also changes the interaction between these platelets. Coulomb-like and multipolar interaction similar to that in electrostatics are discovered and can be readily switched by shining light of different polarization. To sum up, we demonstrate that combining the unique properties of colloidal particles and facile responses of liquid crystals can lead to richness of soft composite material behavior and potentials of engineering a host of technological applications ranging from colloidal motors to micro-actuators and smart windows.

Available for download on Thursday, January 27, 2022

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