Understanding AM feedstock recyclability using small angle X-ray scattering

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Utilizing small angle X-ray scattering to understand material failures and improve material lifetime

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Tailor made polymeric feedstocks for additive manufacturing using polymer science principles

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Evolution of microscopic heterogeneity and dynamics in choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) are an emerging class of non-aqueous solvents that are potentially scalable, easy to prepare and functionalize for many applications ranging from biomass processing to energy storage technologies. Predictive understanding of the fundamental correlations between local structure and macroscopic properties is needed to exploit the large design space and tunability of DESs for specific applications. Here, we employ a range of computational and experimental techniques that span length-scales from molecular to macroscopic and timescales from picoseconds to seconds to study the evolution of structure and dynamics in model DESs, namely Glyceline and Ethaline, starting from the parent compounds. We show that systematic addition of choline chloride leads to microscopic heterogeneities that alter the primary structural relaxation in glycerol and ethyleneglycol and result in new dynamic modes that are strongly correlated to the macroscopic properties of the DES formed

Phase transitions of lyotropic liquid crystalline polymers: Effect of fluctuations and disorder

When a solution of rod-like polymers is subjected to a reduction in solvent quality, it is theoretically predicted that a biphasic system will result. This is not what is observed however as the result is gelation; the formation of a three dimensional self-supporting polymer rich network. The lyotropic system of poly ($\gamma$-benzyl l-glutamate) (PBLG) in benzyl alcohol (BA) has been studied on a molecular level as the system is brought from the high temperature phases towards the gel in hopes of understanding the processes that occur that result in gelation. Low angle light scattering and small angle neutron scattering were used to monitor the configuration of the PBLG molecule as the system was brought from the isotropic to gel phase and to study the gel itself. Quasi-elastic neutron scattering was utilized to measure the local dynamics of the PBLG molecule as the system is brought from the cholesteric to the gel phase. The results show that an aggregation of PBLG molecules exists up to 80\sp\circC in the isotropic phase and the size of the aggregate changes little as the gelation threshold is approached. As gelation occurs, the size of the aggregate increase substantially. The thermal history of the solution in the isotropic phase also affects the local structure of the resultant gel. Short annealing times result in an open structure similar to an aggregate that is formed via the clustering of clusters mechanism and longer annealing times allow the aggregate to relax and results in a denser, more compact structure. Quasi-elastic neutron scattering demonstrated that the local dynamics of the polymer are continuous and unhindered in the cholesteric phase, but become more constrained and jump like as the system enters the gel phase. The effect of quenched disorder on the nematic to isotropic transition of a liquid crystal has also been studied. Using Monte Carlo simulation and differential scanning calorimetry, it was seen that quenched disorder will interrupt the ability of the liquid crystal to correlate and this will lower the transition temperature, round and lower the heat capacity peak, and possibly change the order of the transition

The Effect of Plant Source on the Properties of Lignin-Based Polyurethanes

This work increases our understanding of the effect of plant source on the mechanical and morphological properties of lignin-based polyurethanes (PUs). Lignin is a polymer that is synthesized inside the plant cell wall and can be used as a polyol to synthesize PUs. The specific aromatic structure of the lignin is heavily reliant on the plant source from which it is extracted. These results show that the mechanical properties of lignin-based PUs differ based on lignin’s plant source. The morphology of lignin-based PUs was examined using atomic force microscopy and scanning electron microscopy and the mechanical properties of lignin-based PU samples were measured using dynamic mechanical analysis and shore hardness (Type A). The thermal analysis and morphology studies demonstrate that all PUs prepared form a multiphase morphology. In these PUs, better mixing was observed in the wheat straw lignin PU samples leading to higher moduli than in the hardwood lignin and softwood lignin PUs whose morphology was dominated by larger aggregates. Independent of the type of the lignin used, increasing the fraction of lignin increased the rigidity of PU. Among the different types of lignin studied, PU with wheat straw soda lignin exhibited storage moduli ~2-fold higher than those of PUs incorporating other lignins. This study also showed that during synthesis all hydroxyl groups in the lignin are not available to react with isocyanates, which alters the number of cross-links formed within the PU and impacts the mechanical properties of the material