Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Kundu, Santanu

Committee Member

Rai, Neeraj

Committee Member

Meng, Dong

Committee Member

Scott, Colleen

Date of Degree

8-8-2023

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

Semiconducting polymers with a conjugated backbone are important for energy storage, conversion, and biomedical field applications. The self-assembly process of these polymers in solutions depends on the polymer concentration and quality of the solvent. The electrical properties of thin films obtained from the solution phase depend on the self-assembled process. Thin films of conjugated polymer gels with percolating networks of self-assembled structures display improved electrical conductivities. In this dissertation, we studied the impact of the secondary gel matrix formed by a low molecular weight gelator, on the self-assembly of conjugated polymers, the preservation of assembled structures in dried gel films and their electrical properties.

The study utilized di-Fmoc-l-Lysine gelator, to form a hybrid gel with poly(3-hexylthiophene) in chloroform. The aggregation of P3HT with the progression of gelation was captured using spectroscopic analysis. The aggregates remain in the interstitial spaces of the fibrillar microstructure of gelator. With restricted mobility and due to higher local concentration, the aggregates formed nanofibriliar structures. Microstructural data indicated the nanostructures formed a percolating network in the dried films with good bulk conductivity, despite conductive polymer content of only 20%.

Conjugated polymers require a high boiling point and toxic halogenated solvents to develop gels limiting their applications. By utilizing the amphiphilic nature of the gelator, a thermoreversible gel was obtained in 1-propanol, by combining it with an isoindigo-based DA polymer, engineered with galactose side chains to improve its solubility in eco-friendly solvents. Uniform distribution of aggregated polymer increased the shear moduli of the gels. The electrical conductivity of the dried gels confirmed the existence of percolated aggregates. Additional solvent systems were explored, such as 1-propanol mixed with chloroform. Although P3HT is insoluble in 1-propanol, by adjusting chloroform and 1-propanol ratio, a stable gel was obtained. The poor solvent, 1-propanol, assists the self-assembly of P3HT, improving the electrical performance of dried hybrid gels.

The findings from this study contribute to a better understanding of the self-assembly of conjugated polymers utilizing molecular gels as templates. It provides a framework for obtaining semiconducting gels for applications in the biomedical field, and for large-scale fabrication of optoelectronic devices.

Semiconducting polymers with a conjugated backbone are important for energy storage, conversion, and biomedical field applications. The self-assembly process of these polymers in solutions depends on the polymer concentration and quality of the solvent. The electrical properties of thin films obtained from the solution phase depend on the self-assembled process. Thin films of conjugated polymer gels with percolating networks of self-assembled structures display improved electrical conductivities. In this dissertation, we studied the impact of the secondary gel matrix formed by a low molecular weight gelator, on the self-assembly of conjugated polymers, the preservation of assembled structures in dried gel films and their electrical properties.

The study utilized di-Fmoc-l-Lysine gelator, to form a hybrid gel with poly(3-hexylthiophene) in chloroform. The aggregation of P3HT with the progression of gelation was captured using spectroscopic analysis. The aggregates remain in the interstitial spaces of the fibrillar microstructure of gelator. With restricted mobility and due to higher local concentration, the aggregates formed nanofibriliar structures. Microstructural data indicated the nanostructures formed a percolating network in the dried films with good bulk conductivity, despite conductive polymer content of only 20%.

Conjugated polymers require a high boiling point and toxic halogenated solvents to develop gels limiting their applications. By utilizing the amphiphilic nature of the gelator, a thermoreversible gel was obtained in 1-propanol, by combining it with an isoindigo-based DA polymer, engineered with galactose side chains to improve its solubility in eco-friendly solvents. Uniform distribution of aggregated polymer increased the shear moduli of the gels. The electrical conductivity of the dried gels confirmed the existence of percolated aggregates. Additional solvent systems were explored, such as 1-propanol mixed with chloroform. Although P3HT is insoluble in 1-propanol, by adjusting chloroform and 1-propanol ratio, a stable gel was obtained. The poor solvent, 1-propanol, assists the self-assembly of P3HT, improving the electrical performance of dried hybrid gels.

The findings from this study contribute to a better understanding of the self-assembly of conjugated polymers utilizing molecular gels as templates. It provides a framework for obtaining semiconducting gels for applications in the biomedical field, and for large-scale fabrication of optoelectronic devices.

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