[CCoE Notice] Materials student defense announcement

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[Dissertation Defense Announcement at the Cullen College of Engineering]
CONTROL OF IMPRINT ABILITY, MORPHOLOGY, AND PHASE BEHAVIOR IN VARIOUS POLYMER THIN FILMS WITH IONIC ADDITIVES

Chuqing Yuan

November 11, 2022; 3:00 PM - 5:00 PM (CST)

Location: Online via Microsoft Teams
 Meeting ID: 245 441 485 150 Passcode: DJvgud

Committee Chair:
Alamgir Karim, Ph.D.

Committee Members:
Haleh Ardebili, Ph.D. | Zhifeng Ren, Ph.D. | Devin L. Shaffer, Ph.D. | John C. Wolfe, Ph.D.

Abstract

Polyacrylonitrile (PAN)-based carbon microstructures have tremendous potential in the electronics industry due to their high carbonization yield and high conductivity. However, because of the crystallinity and high melting point nature, pure PAN thin films are challenging to get patterned at routine oven temperatures via capillary force lithography (CFL), a facile and straightforward lithographic technique. In this dissertation, I demonstrate two feasible approaches to enhance the CFL imprint ability of PAN-based thin films. The first approach is adding 10 wt.% ionic liquid (IL), EMIM-TFSI, to suppress the crystallization and provide the required mobility for mold filling. The effect of IL additive concentration, annealing temperature, and hold time with PDMS mask on the imprint ability of PAN are well-correlated in a balancing act. The resulting patterned films demonstrate extraordinary IL recovery ability and thermal stability. The second approach introduces a blend opponent, PMMA, into PAN to take advantage of phase separation and PMMA plasticization. PAN domains become mobile with sufficient PMMA addition and are well-aligned in PDMS channels at M75/N25 composition.
Nowadays, ionic liquid crystal (ILC) surpasses IL in many ways because it combines the characteristics of IL and liquid crystal (LC). IL itself can assist block copolymer (BCP) self-assembly and provide ionic conductivity. However, the effect of ILC on the BCP self-assembly is not well-studied as BCP/IL system and needs to be explored. In this dissertation, I examine the effect of a viologen-based thermotropic ILC on the self-assembly of lamellar PS-b-PMMA and cylindrical PS-b-PEO in thin films under different annealing methods and conditions. TOF-SIMS and GISAXS determine that ILC selectively swells into PMMA domains in PS-b-PMMA, which is greatly affected by the ILC thermotropic phase transition. Also, PS-b-PMMA/ILC demonstrates a significant difference in phase behavior and morphology between static thermal annealing and cold zone annealing (CZA). For PS-b-PEO/ILC, a specific 5 wt% ILC facilities perpendicular-oriented cylindrical morphology in as-cast low Mw PS-b-PEO. ILC selective swelling behavior in PEO domains enables tuning the size of vertical PEO cylinders in as-cast high Mw PS-b-PEO with varying ILC concentrations.

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