Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 98-103).

Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / A superhydrophobic surface combines chemical hydrophobicity with roughness. Due to the surface tension of water, the water cannot penetrate between the roughness elements, which remain filled with dissolved gas; the water surface thus remains suspended over the gas, creating shear free flow regions. In this study, we conducted experiments to study drag in flows over deformable superhydrophobic walls. Our superhydrophobic walls were fabricated by lithographically defining pores on 1-um-thick silicon nitride membranes; the membranes were then treated with silane to make them hydrophobic. For the flow experiments, we fabricated microchannels in which one wall was the porous and deformable superhydrophobic membrane and the other wall was a rigid hydrophilic surface. We measured the pressure drop and the flow rate in these microchannels; we simultaneously used white light interferometry to visualize the deformations of the superhydrophobic membrane. From both sets of measurements, we determined the relevant quantities, including the slip length at the liquid-solid interface. The results from these measurements suggest that the drag onthese deformable superhydrophobic walls is due to a complex interplay between wall deformation and shear-free flow; in most cases, it is not possible to directly observe the drag reduction due to the reduction in the solid-liquid interfacial area. / 2031-01-01

The purpose of this work is to investigate local field type corrections to electrical transport properties and in particular small polaron hopping conductivity. The question of local field corrections to transport properties has been considered for some time. Recently this question has become of particular interest for small polaron hopping conduction. Such corrections were considered as a possible explanation for the large jump parameters inferred in fitting the electric field dependence of the electrical conductivity of certain transition metal oxide glasses in which conduction is believed to occur via thermally activated small polaron hopping. Local field corrections are well established in determining the dielectric constant and optical properties at a single atomic site. Tessman et al have shown that the assumption of a normal Lorentz term gives excellent agreement between computed and measured polarizabilities in alkali halide crystals at optical frequencies. Adler has proved, using a self-consistent field theory that the standard Lorentz term arises in the tight binding limit. Also a full quantum mechanical treatment of the frequency and wave-number dependent dielectric constant including local field effect has been given by Wiser. It is shown that the dielectric constant splits into an atomic term that describes the motion of the electron around each atom and an acceleration term which describes the motion from atom to atom and that acceleration term contains no local field correction. Lidiard has discussed Lorentz type corrections to the diffusion coefficient in ionic conductivity. He argued that no Lorentz correction should be applied, since the Lorentz cavity must always be centred on the hopping carrier; thus, the Lorentz internal field can do no work as the carrier moves from one site to another. This view is strongly supported by the close agreement between ionic diffusion coefficients obtained from conductivity data and NMR relaxation and isotopic diffusion. It has been argued by Munn in several papers without detailed justification that the microscopic mobility does give the polaron velocity in terms of a local field. This argument is in conflict with that of Lidiard. However this question had not been considered explicitly for the case of electrical transport in the hopping limit. It is the intent of the present work to study the local field problem. In the first chapter we give a general description of the local electric field concept which is straight review. Chapters II and III are concerned with the question of local field corrections to the small polaron hopping conduction and the Hall mobility. In Chapter IV the results of Chapter II are applied to ac impurity hopping conduction. Finally in Chapter V we study the band motion of electrons using a theory of transport based on quantum mechanical principles.

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Decompositions of solids are typically of the form: A(s) ----> B(s) + gases. Symmetry-controlled routes (based on known and hypothetical crystal structures) for transforming the solid reactant into the solid product were devised as possible decomposition pathways. Lattice energies of the reactants, of the postulated transient intermediate structures and of the final solid products were then estimated by crystal modelling procedures. Profiles of lattice energy changes during the proposed decomposition routes were constructed and any energy barriers were compared with experimental activation energies reported for the thermal decompositions. The crystal modelling was performed with the computer program WMIN. Calculation of the lattice energies involved the development of a model potential for the perfect lattice and the evaluation of the interatomic parameters. The potential was based on the Born model of ionic solids using the Buckingham potential (Ø(r)= Ae⁻r/p - C/r⁶) to describe the short-range energy contribution. Empirical fitting was used to establish reliable interatomic energy parameters. The reliability of the interatomic potentials was assessed by calculating crystal structures and lattice energies (which were not included in the fitting). The particular reactions selected for modelling were the decompositions of the alkaline-earth metal (Ca, Sr, Ba) peroxides and carbonates: M0₂(s) ---> MO(s) + ¹/₂0₂(g) MC0₃(s) ---> MO(s) + CO₂(g)The lattice energies calculated for the known structures were in good agreement with reported values, (except for Ba0₂ and BaC0₃) which provided support for the adequacy of the potential model used. Activation energies calculated for the decomposition of the carbonates were in the correct order but hlgher than experimental values, i. e., 422, 422, 465 and 499 kJ mol̄̄⁻¹ compared to the experimental values of 205, 87(?), 222 and 283 kJ mol̄̄⁻¹ for CaC0₃ (calcite), CaC0₃(aragonite), SrC0₃ and BaC0₃. The values calculated for the peroxides (91 and 100 kJ mol⁻¹ compared to the experimental values of 119 and 185 kJ mol⁻¹ for Sr0₂ and Ba0₂ respectively) were less satisfactory but could be a reflection of the poor structural data used for the peroxides. The significance of this approach to the modelling of solid decompositions is discussed.

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