A better understanding of amorphous aluminum oxide’s structure and electronic properties is obtained through combined experimental and computational approaches. Grazing incidence X-ray scattering measurements were carried out on aluminum oxide thin films grown using thermal atomic layer deposition. The corresponding pair distribution functions (PDFs) showed structures similar to previously reported PDFs of solid-state amorphous alumina and molten alumina. Structural models based on crystalline alumina polymorphs (PDFgui) and amorphous alumina (molecular dynamics, MD) were examined for structural comparisons to the experimental PDF data. Smaller MD models were optimized and verified against larger models to allow for quantum chemical electronic structure calculations. The electronic structure of the amorphous alumina models yields additional insight into the band structure and electronic defects present in amorphous alumina that are not present in crystalline samples.

A new method based on quasi-independent parallel simulations approach, replica-averaging, has been developed to study the influence of flow on mechanical force-mediated polymer processes such as denaturation and breaking of bonds. This method considerably mitigates the unphysical prediction of force-mediated events inherent in Brownian dynamics (BD) polymer chain simulations that employ instantaneous force profile-based criteria to identify the occurrence of such events. This inaccuracy in predicting force-mediated event kinetics is due to high fluctuations of the instantaneous force profile around the average force. Replica-averaging reduces such high fluctuation effects by computing a force profile that faithfully represents the average force profile of the polymer chain conformation, which is then used to predict reactive events. For transient conformation conditions, the replica-averaged method more accurately predicts mechano-reactive kinetics than the time-averaged method, typically employed to reduce the unphysical prediction of force-mediated events in BD simulations. Further, the influence of the proposed replica-averaging method parameters on the accuracy of predicting the true average force profile along the polymer is discussed.

Unraveling kinetics of collapsed polymers in relatively low strain rate extensional flow is explored via coarse-grained Brownian dynamics (BD) simulations. Unraveling probability versus the strain rate was computed for varying amounts of exposure time to flow and shown to exhibit highly non-linear behavior. For the strain rate approximately one-third of the critical strain rate, no unraveling events were observed even for the longest simulation duration explored. Statistical modeling is performed on the distribution of time of exposure to flow before polymer unraveling occurred for strain rates at which sufficient unraveling events were observed. The model thus constructed is used to evaluate unraveling kinetics for strain rates for which unraveling events are not observed in BD simulations. Results indicate a highly non-linear influence of the strain rate on the energy profile associated with the unraveling transition and this is related to the long length polymeric protrusions required to drive unraveling in such flows. As an example application of the results obtained, a quantitative prediction is made for extensional flow strain rates in which the self-associating polymeric blood protein von Willebrand Factor will exhibit pathological unraveling.