Theses and Dissertations

ORCID

https://orcid.org/0000-0003-2880-9306

Advisor

Kundu, Santanu

Committee Member

Toghiani, Hossein

Committee Member

Rai, Neeraj

Committee Member

Scott, Colleen

Date of Degree

5-10-2024

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Chemical Engineering

Degree Name

Doctor of Philosophy (Ph.D)

College

James Worth Bagley College of Engineering

Department

Dave C. Swalm School of Chemical Engineering

Abstract

The electrospinning technique is an attractive route for processing conjugated polymers (CPs) in a significant quantity for large-scale applications. However, the processing-structure-property relationship of the electrospinning process for CPs is not well understood. This dissertation provides a fundamental understanding regarding the structure development of CPs in electrospun fibers because of different processing conditions and relates that to fiber properties. Electrospinning was conducted for a mixture of polyethylene oxide (PEO) and poly(3-hexylthiophene) (P3HT) of three different molecular weights and two aging conditions: freshly prepared and 24 h aged spinning solutions. The aging of the spinning solution led to the self-assembly of P3HT chains, particularly with dominant H-aggregation for the higher molecular weight of P3HT. Those preexisting H-aggregates in the solution were retained and even increased in the fibers during electrospinning. Single fiber electrical conductivity, measured using a custom-built technique, has been found to increase with increasing molecular weight, particularly, a significant enhancement of that was observed for the fibers from the aged solution compared to the fibers obtained from the freshly prepared solution. Blending insulating polymers in CPs for electrospinning can hamper charge-carrier transfer, particularly when a large amount of insulating polymers is used for electrospinning. Thus, we adopted a coaxial electrospinning approach to avoid the blending of insulating components and to preserve the electrical properties of CPs. The coaxial fiber consisted of flexible polymers such as butyl rubber (BR), polymethylmethacrylate (PMMA), and PEO in the core and P3HT in the shell. BR in the core led to highly stretchable fibers. Further, P3HT in the shell facilitated the direct doping of the fiber without any post-treatment. The electrical conductivity of the doped fibers did not change significantly up to 400% strain and remained almost unchanged under cyclic loading, showing excellent mechanical reversibility. The general applicability of the spinning approach developed here has been demonstrated by successfully electrospinning donor-acceptor CP at the shell of the coaxial fibers. Our results provide new understandings linking the processing of CPs in fibers, the structural evolution of CPs in the fibers, and the corresponding electrical properties as a function of molecular weight, aging of solution, and mechanical loading.

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