Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Sylvia W. Thomas, Ph.D.

Committee Member

Arash Takshi, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Norma Alcantar, Ph.D.

Committee Member

Vincenzo Guarino, Ph.D.

Committee Member

Chang-Yong Nam, Ph.D.

Keywords

BBL, Coaxial Junctions, Nanofibers, P3HT, Semiconductors, Sensors

Abstract

Electrospinning has become one of the most interesting techniques for fabricating nanofibers for multiple applications. The high surface-to-volume ratio nanofibers offer make the perfect structure for filters, sensors, and fiber-based electronics that could lead to a wide range of flexible electronics applications. This technique makes organic semiconducting polymers a promising alternative for single fiber electronics structures. Indeed, a wide variety of structures can be fabricated using electrostatic techniques for polymer manipulation from droplets, fibers, and coaxial structures. Although techniques such as electrospinning led the use of electrostatic forces to generate fibers of a precursor solution, electrospinning requires large enough polymer chains to enhance entanglement. This leads to the formation of long nanofibers, putting aside polymers with low molecular weight and to the formation of beads by a spraying behavior. Thus, development of a multilayer process for the formation of organic semiconductive coaxial fibers is imperative and the subject of this dissertation. Organic semiconductive polymer such as the p-type P3HT and the n-type BBL were used in this research. Fibers of P3HT were fabricated in conjunction with an auxiliary polymer to mechanically help the formation of fibers. P3HT has been shown to form fibers that can be embedded for the fabrication of diodes, sensors, and as a negatively charges molecule adsorbent. BBL thin films were studied as a gas sensor for volatile organic compounds (VOC’s). Most importantly, for the first time, a nanofiber comprising P3HT core / BBL shell coaxial structure was fabricated and morphologically characterized.

These coaxial nanofibers were fabricated using the electrospinning technique by taking advantage of their solvent orthogonality. Fast and abrupt production resulted in a wide population of nanofibers in the nanoscale. Previous electrical characterization was performed to the P3HT fibers in different embodiments showing tunable behavior under UV radiation. Gas sensing on BBL thin films were related to the known concentration for different analytes. Coaxial nanofibers were characterized using transmission electron microscopy (TEM), demonstrating the formation of semiconductive nanofibers coaxial arrangements using the electrospinning technique. These advancements demonstrate the ability of forming a single nanofiber junction, the possibility of a cylindrical p-n junction, and create the ability to fabricate single fiber devices increasing the surface-to-volume ratio, ultimately improving the sensing response under a sensing embodiment.

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