Construction and Characterization of Grain Boundaries in Diacetylene Polymer Bicrystals.
Abstract
The goal of this dissertation is to develop techniques to isolate grain boundary defects with controlled geometries by creating polymer bicrystals and characterize their contribution to macroscopic properties. Diacetylene polymer bicrystals were obtained by constructing diacetylene monomer bicrystal precursors followed by a monomer-polymer solid-state phase transformation. The construction of diacetylene monomer bicrystals started with two seed crystals which were brought into contact with one another to create a grain boundary with controlled geometry. The mechanisms of the diacetylene monomer-polymer phase transformation have been studied by dynamic low-dose transmission electron microscopy (TEM) and white beam synchrotron X-ray topography (WBSXT). In thin film DCHD diacetylene crystals, the phase transformation was quasi-homogeneous with planar defects developing during the intermediate stages but vanishing at the end of the polymerization. In bulk DCHD diacetylene crystals, internal defects such as subgrain boundaries, cracks, and pores remained present after the phase transformation was completed. However, in bulk bis (p-toluene sulphonate) ester of 2,4-hexadiyne -1,6-diol (pTS) diacetylene, defects developed during the phase transformation but disappeared at the final stage of the phase transformation. The monomer-polymer phase transformation in DCHD diacetylene is analogous to a martensite phase transformation and has three invariant planes: (2 2 0), (2-2 0), and (0 0 1). There is an 8% and 18% expansion along (0 0 1) and the normal of (2-2 0), and 21% contraction along the normal of (2 2 0) during the phase transformation. Mechanical strength and transient photoconductivity have been tested on engineered DCHD diacetylene polymer bicrystal samples. Both of these properties systematically decreased as a function of the misorientation introduced at grain boundaries, revealing information about the extent of covalent bond connectivity across the grain boundary interfaces.
- Publication:
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Ph.D. Thesis
- Pub Date:
- January 1995
- Bibcode:
- 1995PhDT........48L
- Keywords:
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- Engineering: Materials Science; Physics: Molecular; Physics: Condensed Matter