Characterizing molecular dynamics of polymer glass and gel phase transitions as a function of time, temperature, and concentration using nuclear magnetic resonance
Dower, April Marie
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Polymers can be used for a variety of applications and impact many aspects of our lives. This thesis investigates the dynamics of polymer gel and glass transitions over different times, temperatures, and concentrations using nuclear magnetic resonance (NMR) with the goal of further understanding these important systems. A polymer/solvent system, hydroxypropylmethylcellulose acetate succinate (HPMCAS) and acetone, was examined using magnetic relaxation correlation and exchange experiments to characterize domains of different molecular mobility over various temperatures and concentrations. Diffusometry was employed to support the results of the 2D relaxometry experiments. A simple relaxometry method to determine glassiness was verified, and characteristic length scales of a polymer solution at different temperatures were quantified using both relaxation exchange methods and diffusion data. Glasslike dynamics were observed in gelled polymer systems above their glass transition temperatures. The thermal gelation properties of colloidal polymer dispersions and the effects of different formulations on dry film formation of a polymer mixture were studied as well. Aging and plasticizer effects were examined in the colloidal polymer dispersions using magnetic relaxation correlation experiments along with diffusion experiments to understand molecular dynamics, and it was concluded that pre-gelation particle aggregates were necessary for the systems to thermally gel. The final polymer study aimed to determine why a formulation using differently-substituted polymer produced dry films with dissimilar mechanical properties than another. Using relaxometry data and quantitative length scales acquired through relaxation exchange, it was found that one mixture retained larger domains of water upon dry film formation, allowing the film to be less brittle.