Date of Award
Spring 3-2022
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
School
Polymer Science and Engineering
Committee Chair
Xiaodan Gu
Committee Chair School
Polymer Science and Engineering
Committee Member 2
Jason D. Azoulay
Committee Member 2 School
Polymer Science and Engineering
Committee Member 3
Sarah E. Morgan
Committee Member 3 School
Polymer Science and Engineering
Committee Member 4
Sergei Nazarenko
Committee Member 4 School
Polymer Science and Engineering
Committee Member 5
Song Guo
Committee Member 5 School
Mathematics and Natural Sciences
Abstract
In contrast to conventional silicon-based electronics, semiconducting polymers show great promise for emerging applications in soft, flexible, and ductile electronic technologies. This is due to their polymeric nature, tailorable structure, and sub-100 nm device thickness. Despite this mechanical novelty, there remains a poor understanding of their structure-property-processing relationships, which has hindered growth within the field. This dissertation elucidates these relationships through investigation of their thermomechanics, and morphological phenomena. This was accomplished through the following projects:
1) To demonstrate the impact of backbone rigidity on semiconducting polymer thermomechanics, we varied the backbone rigidity of an NDI-based polymer by inserting flexible methylene units of varying lengths along the backbone of the monomer unit. Incorporation of the spacer resulted in a vast reduction of the glass transition temperature (Tg) and profound improvements in ductility.
2)We developed a free-standing tensile technique that enabled the characterization of polystyrene and poly(3-hexylthiophene) films down to 19 nm and 80 nm, respectively. Confinement was demonstrated to impact yield stress and strain at failure of polystyrene films, while modulus was relatively unaffected, despite literature suggestion of a sub-room temperature Tg. We then compared water-supported and free-standing films to elucidate their interfacial influence on the observed mechanical performance.
3) Amide and urea moieties were incorporated into a DPP-based polymer to demonstrate the role of hydrogen bonding strength on thermomechanical performance. Amide and urea were discovered to minimize and promote crystallinity, respectively, which led to a 400% increase in strain at failure for the amide-containing polymer. This finding demonstrated that hydrogen bonding may dictate mechanical performance through control of the crystalline morphology, rather than energy dissipation.
4) Due to the semicrystalline nature of semiconducting polymers, it has been postulated that they may possess a rigid amorphous fraction (RAF) which may dictate their optoelectronic performance. To illuminate the existence and impact of the RAF on semiconducting polymer performance we established a spectroscopic ellipsometry method to fully characterize their temperature-dependent thickness, optical profile, and degree of anisotropy. All semicrystalline semiconducting polymers were observed to possess a RAF which strongly dictated their optoelectronic performance.
ORCID ID
0000-0002-0101-8507
Recommended Citation
Galuska, Luke, "THERMOMECHANICS OF SEMICONDUCTING POLYMERS AND THEIR MORPHOLOGICAL PHENOMENA" (2022). Dissertations. 1985.
https://aquila.usm.edu/dissertations/1985
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