UNDERSTANDING THE EFFECTS OF CONJUGATION BREAK SPACERS ON STRUCTURE−PROPERTY...

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UNDERSTANDING THE EFFECTS OF CONJUGATION BREAK SPACERS ON STRUCTURE−PROPERTY RELATIONSHIPS IN PARTIALLY CONJUGATED SEMICONDUCTING POLYMERS AND THEIR THIN FILMS

thesis
posted on 29.04.2021, 02:50 by William W McNuttWilliam W McNutt
The field of semiconducting conjugated polymers has grown tremendously over the past few decades with innovations expanding the use of conjugated polymers into several devices such as transistors, light emitting diodes, and biocompatible electronics. For transistor devices, charge carrier mobility has rivaled the performance of amorphous silicon. The intrinsic properties of organic materials make them extremely attractive for further development and application. Organic materials are synonymous with terms such as lightweight, robust, flexible, and stretchable. A major advantage of conjugated polymers is their ability to be rendered solution processable with the alluring potential for large-area green manufacturing of electronic devices. However, these properties often fall short of their potential. Often strain engineering is often employed for favorable mechanical properties of polymer thin films. The use of toxic chlorinated solvents is commonplace for the manufacturing of polymer thin films, raising both health and environmental concerns on top of prohibitively increasing manufacturing costs. Deeper understanding of the structure−property relationships of polymers and their thin films is necessary for this class of materials to reach their full potential.
In this thesis, we seek to expand upon the previously demonstrated complementary semiconducting polymer blends (c-SPBs) by presenting the first n-type matrix polymers and their c-SPBs. The new n-type matrix polymers had favorable thermal properties with melting points between 55-100 °C allowing for the lowest temperature solvent-free melt-processed polymer thin films for organic transistors to date. N-type 5% c-SPB transistors displayed mobilities 100-fold that of pure n-type matrix polymers despite an extremely disordered polymer thin film microstructure. Additionally, the glass transition temperature was significantly lowered to below room temperature allowing for operation in the viscoelastic state. Conjugation break spacers (CBS) lead to low molecular weight of entanglement in combination with extremely high molecular weight for thin film ductility up to 400%, a record for deformable electronics. The mechanism of deformation to explain this incredible mechanical performance was extensively studied through a combination of X-ray and polarized UV-Vis spectroscopy. Finally, we investigated the effect of isomer structure has on the properties of conjugation polymers utilizing diazines to decouple the effects of spatial arrangement from heteroatom placement.

Funding

CAREER: Impact of Flow-Induced Chain Alignment in Melt-Processed Complementary Semiconducting Polymer Blends

Directorate for Mathematical & Physical Sciences

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History

Degree Type

Doctor of Philosophy

Department

Chemistry

Campus location

West Lafayette

Advisor/Supervisor/Committee Chair

Jianguo Mei

Additional Committee Member 2

P. V. Ramachandran

Additional Committee Member 3

Mingji Dai

Additional Committee Member 4

Jonathan Wilker

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