Doctoral Dissertations

Date of Award

12-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Gila Stein

Committee Members

Joshua Sangoro, Michael Kilbey, Emmanouil Doxastakis, Alexei Sokolov

Abstract

Functional block copolymers are of increasing interest for their ability to combine the functional properties of one polymer, such as a polymer electrolyte or semiconductor, with the mechanical properties of another polymer. Balancing properties in this way can be challenging, however, due to the complex relationship between self-assembled morphology and resulting properties. Interface effects in particular, whether due to confinement within a self-assembled domain or at macroscopic boundary, are poorly understood in such functional block copolymers. This dissertation consists of two main thrusts, each investigating confinement or interfacial effects in a different functional block copolymer system. The first thrust focuses on the relationship between crystallization and self-assembly in diblock block copolymers of poly(3-dodecylthiophene) (P3DDT) and poly(2-vinylpyridine) (P2VP). Through the use of in-situ and time-resolved X-ray scattering, three distinct modes of P3DDT crystallization were observed. These modes were found to depend on both the degree of crystallinity of the P3DDT block as well as the morphology of the block copolymer. Since degree of crystallization in these materials can, in many cases, be tuned without impacting self-assembled morphology (and vice-versa), these findings demonstrate that in this system the parameters that govern classical block copolymer self-assembly are decoupled from those that govern crystallization. In the second thrust, the impact of interfacial order on the ionic conductivity in block copolymers of polystyrene (PS) and a polymeric ionic liquid (PIL) is investigated. Through a combination of X-ray scattering, impedance spectroscopy, and island and holes studies on thin films, it was found that the formation of highly-oriented lamellar layers at film interfaces, which results in significant anisotropy in the ionic conductivity of PS-PIL block copolymers. In-plane conductivity was found to be enhanced in these materials by as much as 18x compared to the through-plane conductivity. Interestingly, a similar phenomenon was observed in a random copolymer of styrene and ionic liquid, with in-plane conductivity enhanced by as much as 3x compared to the through-plane conductivity. This suggests that interfacial reordering even at very small length scales, which has been observed in amphiphilic random copolymers with large pendant groups, is sufficient to produce significant anisotropy in the ionic conductivity of the film.

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