Insights into Pressure-Temperature Induced Morphology and Mesophase Formation in the Non-Mesogenic Polymer Polyethylene OxidetextClevinger, Tobias BcreatorMathiowitz, EdithAdvisorSrivastava, VikasReaderGray, MarissaReaderBrown University. Biology and Medicine: Biomedical Engineeringsponsor2021x, 97 p.born digitalThesis (Sc. M.)--Brown University, 2021thesesThis work aimed to identify the morphological effects of heat and pressure on high molecular weight (300,000 kDa) polyethylene oxide, with a specific focus on identifying evidence of mesophase formation in the material. Polarized microscopy, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and x-ray diffraction analysis were all performed for this purpose. Samples processed at 60°C showed a linear relationship between pressing force and the resulting pressure on the samples. Polarized microscopy showed the development of birefringence in samples processed at 60°C and pressures above 1900 psi, as well as in samples that had no pressure applied. Differential scanning calorimetry demonstrated that heat and pressure caused samples to increase in melting and crystallization temperature. Additionally, sample heat of fusion and crystallinity increased proportionally to the pressure applied during treatment. However, the material’s glass transition could not be seen, nor any phenomena associated with mesophase formation. Infrared spectroscopy showed several characterizing phenomena between samples: blue shifting and peak broadening of the 1050-1150 cm-1 band, peak intensity at 840 cm-1, and peak intensity/ratio at 940 and 960 cm-1. These phenomena varied much more widely in birefringent sample regions than non-birefringent center regions. Finally, x-ray diffraction analysis of samples processed at varying temperatures and high pressures (over 10,000 psi) showed no characteristic evidence of mesophase formation but did show a change in the prevalence of different crystalline planes in the material structure, suggesting that reorientation occurred. Overall, no evidence of mesophase formation was seen. Evidence instead suggests an increase in crystallinity and a change in crystal orientation.PolymersBiomedical engineeringBiomedical materialsPolyethylene oxideEnglishRPB20210607