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Anchoring-Induced Topological Defects in Nematic Liquid Crystals: Core Relaxation Mechanisms and Electro-Optics

Murray, Bryce S, Murray
http://rave.ohiolink.edu/etdc/view?acc_num=case1531143058239933

Abstract Details

2018, Doctor of Philosophy, Case Western Reserve University, Physics.
I present a body of work regarding topological defects (TDs) in nematic liquid crystals. Defects having specific strengths were created in specified locations using atomic force microscope (AFM) lithography and the means by which the defects relieve the diverging strain energy near their cores was characterized as a function of cell depth and by probing with an electric field. I also work towards nanoparticle trapping in the scribed cores by doping a host liquid crystal with fluorescent nano-emitters. The technique of scribing an easy axis by AFM lithography was extended by writing Python scripts that produce densely-packed paths for the AFM tip to follow. I create several arrays of defects using this method in thin cells. I then probe the structure of the nematic director near each scribed core by applying a perpendicular electric field to a positive anisotropy liquid crystal. Of interest is the means by which the TDs relax the diverging energy at the defect cores. I show qualitatively that smaller cell depths promote defect splitting, whereas thicker cells promote defect escape, i.e., the director rotates out of the plane. The voltage profile of the transmitted intensity under crossed polarizers was examined, and shows that the liquid crystal can have a Freedericksz threshold voltage near a split defect, but not near an escaped defect. I then assemble thick cells, such that the disclination lines caused by the scribing run near the master surface and terminate on nearest-neighbors. I apply an in-plane field and show that the disclinations can deflect, interact, and can swap termination partners to effect a change in orientation of 90$^\circ$. The local electric field required to make the disclinations interact was measured. Then I consider a technique whereby the diverging energy of the defect cores can be relaxed by suspending nano-emitters, specifically quantum and carbon dots, into the liquid crystal. We make progress towards trapping these nanoparticles in scribed defects. I include a description of some work done towards near-field optical scanning microscopy in thin nematic films. As a whole, this work serves to create TDs and explore several of their basic structural and electro-optic properties.
Charles Rosenblatt (Advisor)
162 p.
Physics
liquid crystal; nematic; topological defect; electro-optics

Recommended Citations

Citations

  • Murray, Murray, B. S. (2018). Anchoring-Induced Topological Defects in Nematic Liquid Crystals: Core Relaxation Mechanisms and Electro-Optics [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1531143058239933

    APA Style (7th edition)

  • Murray, Murray, Bryce. Anchoring-Induced Topological Defects in Nematic Liquid Crystals: Core Relaxation Mechanisms and Electro-Optics. 2018. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1531143058239933.

    MLA Style (8th edition)

  • Murray, Murray, Bryce. "Anchoring-Induced Topological Defects in Nematic Liquid Crystals: Core Relaxation Mechanisms and Electro-Optics." Doctoral dissertation, Case Western Reserve University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1531143058239933

    Chicago Manual of Style (17th edition)

case1531143058239933
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© 2018, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.