Theses and Dissertations at Montana State University (MSU)
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Item Characterizing molecular dynamics of polymer glass and gel phase transitions as a function of time, temperature, and concentration using nuclear magnetic resonance(Montana State University - Bozeman, College of Engineering, 2016) Dower, April Marie; Chairperson, Graduate Committee: Joseph D. SeymourPolymers 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.Item NMR of HPMCAS/acetone mixtures to characterize concentration and temperature dependent molecular dynamics and inform SDD droplet drying models(Montana State University - Bozeman, College of Engineering, 2014) Williamson, Nathan Hu; Chairperson, Graduate Committee: Joseph D. SeymourHydroxypropyl methylcellulose acetate succinate (HPMCAS)-based spray-dried dispersions (SDDs) have been shown to offer significant bioavailability enhancement for drugs with low aqueous solubility. However, the impact of macroscale process conditions on microscale droplet drying and the impact of droplet drying history on SDD physical stability, dissolution performance and particle properties are not well understood. Mass transfer to the droplet surface is diffusion limited, and quantifying the mutual diffusivity over the solvent content and wet-bulb temperatures experienced during drying is crucial to modeling droplet drying. This research used nuclear magnetic resonance (NMR) to probe the concentration and temperature dependence of molecular scale interactions within binary systems of HPMCAS polymer and acetone. This data can be incorporated into SDD droplet drying models. Following the generalized droplet drying model of Handscomb and Kraft [1], a specific SDD modeling procedure was developed. A preliminary form was coded in MATLAB using the finite difference method to approximate the drying time-dependent solvent concentration profiles over the changing droplet radius based on the governing equation for mass conservation. Mixtures of HPMCAS with acetone and wet placebo SDD were tested using high-field NMR. Pulsed gradient stimulated echo (PGSTE) NMR experiments resolved self-diffusion of solvent and polymer. Solvent concentration dependence of the mutual diffusivity was related to a free-volume fit of the acetone self-diffusivity. Multidimensional T 1-T 2 correlation and T 2-T 2 exchange experiments separated proton populations based on correlations of spin-lattice T 1 to spin-spin T 2 relaxation times and discerned time-dependent mixing between T 2 populations. T 1 and T 2 relaxation times depend on the mediation of dipolar coupling by rotational motions; therefore these experiments indicate molecular rotational mobility. Temperature dependence of self-diffusivity and T 1-T 2 correlation measured within a rubbery as well as a glassy HPMCAS/acetone sample indicated that these measurements can determine the thermodynamic phase of polymer-solvent systems. Progression of the SDD droplet drying model and the fundamental aspect of the research on polyelectrolyte and polymer dynamics expanded the current knowledge of polymer glass transition behavior, network formation, and aging. This research demonstrates the potential use of NMR to characterize and quantify mobility and mass transfer of polymers and other pharmaceutically-relevant materials.