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THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING
GEORGIA INSTITUTE OF TECHNOLOGY
Under the provisions of the regulations for the degree
DOCTOR OF PHILOSOPHY
on Wednesday, November 4, 2020
10:00 AM
via
BlueJeans Video Conferencing
https://bluejeans.com/958979519
will be held the
DISSERTATION PROPOSAL DEFENSE
for
Kellina J. Pierce
"Confinement and External Fields Effects on Cellulose Nanocrystals’ Lyotropic Liquid Crystal Behavior”
Committee Members
Prof. Vladimir V. Tsurkuk, Advisor, MSE
Prof. Alberto Fernández-Nieves, PHYS
Prof. Karl Jacob, MSE
Prof. Meisha Shofner, MSE
Mike McConney, Ph.D., Air Force Research Lab
Dhriti Nepal, Ph.D., Air Force Research Lab
Abstract:
Bioderived materials such as cellulose nanocrystals (CNCs) have inherent structural organization that can be exploited for the control of dimensionality, periodicity, and functionality of biocompatible and photonic appropriate materials. However, precise control and tunablility of organized cellulose nanocrystal-based materials is challenging due to the random organization of the chiral nematic structure, called tactoids, during evaporation induced self-assembly (EISA) of solid films. The proposed research aims to control the lyotropic liquid crystal (LC) alignment of CNCs by (i) utilizing geometric confinement for asymmetric evaporation that induces directional flow, (ii) direct chemical modification of the surface groups for control of inter-particle interactions, and (iii) applying magnetic and/ or electric fields for uniform and patterned orientation. The main hypothesis of the proposed research is that the chiral nematic structure of CNC materials can be used as a foundation for selective complex structure formation beyond traditional polydomain-like materials with poorly-defined iridescence and polarization.
The first task intends to utilize capillary conferment and chemical modification of the CNCs to induce uniform alignment of the lyotropic liquid crystal phase. Sulfate esterification of the CNCs with a pyrogallol and the addition of a covalent bond stabilizer will improve the films’ durability under confinement and provide insight on the limitations of directed evaporation of CNC films. The second task will employ magnetic nanoparticles and weak magnetic fields to selectively pattern cellulose films via localized changes in their helical organization. Magnetic nanoparticles will be used to increase the magnetic susceptibility of CNC suspensions for direct precision patterning in the films. Lastly, the third task will make use of electric fields to investigate dynamic changes in the CNCs’ lyotropic liquid crystal phase in liquid and hydrogel materials to ultimately fabricate a solid state material with controlled, frozen helicoidal organization. Due to the disturbance of the hydrogen-bonding network of water when subjected to electric fields, thorough investigation of chemically modified CNCs in nonaqueous solvents will be particularly instrumental for this task to induce reversible pattern formation via electric field stimulation.
Achieving these goals will offer fundamental insight to strengthen CNC materials’ uniformity and their liquid crystal behavior and the resulting flexible, organized films with LC phase-derived organization. As such, this will be the groundwork to define uses for responsive and tunable biopolymer systems to design ordered chiral nanocomposites. This work will advance dynamic control over cellulose nanocrystal films and widen the breath of multi-stimuli responsive, biocompatible hydrogels for biosensors and tunable optical reflectors.
