Liquid Crystal Transitions and Deformations Due to Colloidal Inclusions, Geometric Confinement, and Magnetic Fields / Sophie A Ettinger.

Format:

Book

Thesis/Dissertation

Author/Creator:

Ettinger, Sophie A., author.

Contributor:

University of Pennsylvania. Physics and Astronomy, degree granting institution.

Language:

English

Subjects (All):

Physics.

Condensed matter physics.

Computational physics.

Electromagnetics.

Physics and Astronomy--Penn dissertations.

Penn dissertations--Physics and Astronomy.

Local Subjects:

Physics.

Condensed matter physics.

Computational physics.

Electromagnetics.

Physics and Astronomy--Penn dissertations.

Penn dissertations--Physics and Astronomy.

Physical Description:

1 online resource (132 pages)

Distribution:

Ann Arbor : ProQuest Dissertations & Theses, 2023

Contained In:

Dissertations Abstracts International 84-12B.

Place of Publication:

[Philadelphia, Pennsylvania] : University of Pennsylvania, 2022.

Language Note:

English

Summary:

This dissertation describes experiments and numerical simulations which explore the director configurations and defects of liquid crystals (LCs) in confined geometries, around micro-and nano-particles, and in the presence of external fields and boundary conditions. Specifically, I report on: 1) the symmetry-breaking alignment and chiral director configurations surrounding micron-sized rods in a lyotropic chromonic liquid crystal (LCLC), 2) magnetic field-induced configuration transitions in radial nematic LC droplets, and 3) defect evolution and dynamics in radial LC droplet coalescence facilitated via surface interaction. In total, this dissertation provides new fundamental understanding on the complex interplay between elastic energy and surface energy, as well as the effect of confining boundaries and external fields. The elucidation of configuration transitions and defect transformations offers insights for multi-functional and reconfigurable soft materials that utilize LC technology. Briefly, in the first experiments, I study equilibrium orientation of rod-like particles in an aligned LCLC. Video microscopy reveals, counterintuitively, that two-thirds of the rods have an equilibrium orientation that is at an angle with respect to the natural orientation of the LCLC far-field director. I discover that the small twist elastic constant of LCLCs promotes chiral director configurations I that modify the natural tendency of rods to orient along the far-field director. In the second set of experiments, investigate the effect of an applied magnetic field on the director configuration in a radial nematic LC droplet. I report the first observation of a magnetic field driven transition from a deformed radial to an axial-with-defect configuration. This work is important because it probes a basic phenomenon, i.e, how LCs respond to external fields, that differs fundamentally from the classic Freedericksz transition in a planar geometry as a result of its topological defect. I use polarization optical microscopy for continuous observation of droplet director fields as a function of magnetic field strength and thereby elucidate the transition and evolving director configurations. In the third set of experiments, I study the coalescence of radial LC droplets. Nematic LC droplets with a topological charge of +1 present a significant energy barrier for droplet coalescence. Specifically, the required spontaneous formation of a topological ring defect prevents two radial LC droplets from merging. I report on the surprising experimental observation of two radial droplets coalescing, facilitated by a low surfactant concentration and interaction with a glass interface.

Notes:

Source: Dissertations Abstracts International, Volume: 84-12, Section: B.

Advisors: Yodh, Arjun G.; Committee members: Collings, Peter J.; Lubensky, Tom C.; Mathijssen, Arnold J. T. M.; Bernstein, Gary M.

Department: Physics and Astronomy.

Ph.D. University of Pennsylvania 2023.

Local Notes:

School code: 0175

ISBN:

9798379753528

Access Restriction:

Restricted for use by site license.