No description available.

Effect of surface treatments on Strength and durability of aluminum 6061-Henkel Hysol EA 9891RP (room temperature curing epoxy) bond was studied using single lap shear, flatwise tensile and wedge crack test. The interfacial strength (IFSS) and % cohesive fracture varied with composite adhesive thickness and 0.03-0.04 mm that maximized the interfacial fracture was chosen to compare surface treatments. The effect of treatments on IFSS and tensile strength increased in the following order: PAA+BR127 (RT) < UT+BR127 (120oC) < Alodine < Alodine+EC3901(RT) < Alodine+BR127 (RT) < PAA < UT < UT+BR127 (RT) < Alodine+EC3901 (90oC) < PAA+EC3901(RT) < PAA+EC3901(90oC) < PAA+BR127 (120oC) < UT+EC3901(90oC) < UT+EC3901(RT) < Alodine+BR127 (120oC). The environmental durability decreased in the following order Alodine+EC3901 (90oC) < Alodine+BR127 (120oC) < PAA+BR127 (120oC) < PAA+EC3901 (90oC) < UT < UT+EC3901 (90oC) < UT+EC3901 (RT) < PAA+EC3901 (RT). PAA and Alodine, combined with BR127 (120 oC) and EC3901 (90oC) are the optimal surface treatments / October 2016

Electrodes implanted into neural systems are known to degrade due to encapsulation by surrounding tissues. The mechanisms of electrode-tissue interactions and prediction of the behavior of electrode are yet to be achieved. This research will aim at establishing the fundamental knowledge of interfacial interactions between the host biological environment and an implanted electrode. We will identify the dynamic mechanisms of such interfacial interactions. Quantitative analysis of the electrical properties of interface will be conducted using Electrochemical Impedance Spectroscopy (EIS). Results will be used to develop a general model to interpret electrical circuitry of the interface. This is expected to expand our understanding in the effects of interfacial interactions to the charge transport. The interfacial interactions of an implanted electrode with neural system will be studied in two types of electrodes: silver and graphene coated. The interfacial impedance of both samples will be studied using EIS. The development of the cellular interaction will be investigated using histological procedure. X-ray photoemission spectroscopy (XPS) will be employed to study the chemical effects on the silver electrodes. Atomic force microscopy and Raman spectroscopy will be used for material characterization of graphene-coated electrodes. In the study of silver electrode, two mechanisms affecting the interfacial impedance are proposed. First is the formation of silver oxide. The other is the immuno-response of tissue encapsulation. Histological results suggest that higher cell density cause higher impedance magnitude at the interface. It is also found that the cellular encapsulation dominates the increase in impedance for longer implanted time. In the study of graphene-coated electrode, it is found that the graphene can strongly prevent the metal substrate from being oxidized. It not only provides good electrical conductivity for signal transport, but also reduces the speed of the accumulation of tissue around the electrode. Such characteristics of graphene have great potential in the application of neural implant. Finally, the dynamic mechanisms of biological interaction are proposed. A model is also developed to represent the general circuitry of the interface between an implanted electrode and the neural system. The model has three major components, which are interfacial double layer, cellular encapsulation, and the substrate. The model presented in this study can compensate for selection and prediction of materials and their behaviors.

It is an important topic for electronic packages to estimate the interfacial bonding strength between dissimilar materials. If it is not strong enough, delamination would arise easily under high temperature, vibration or collision. Its reliability will be reduced. The study on interfacial fracture behavior between epoxy resin and die based on experimental and numerical analyses is investigated, and it is useful to judge where the delamination happens . In terms of interfacial fracture mechanics, the critical strain energy release rate (G ) of crack tip is related to the phase angle (£r ) . Considering the interface of the epoxy /die existing a tiny crack, the compact mixed mode (CMM) fixture is used to decide the critical load . Finally , we adopt the finite element method to calculate that the critical strain energy release rate (G ) and the phase angle (£r ) in comparison with empirical results .

High quality (Q) factor whispering gallery modes (WGMs) can induce nonlinear effects in liquid droplets through mechanisms such as radiation pressure, light scattering, thermocapillarity, Kerr nonlinearity, and thermal effect. However, such nonlinear effects have yet to be thoroughly investigated and compared in the literature. In this study, we first investigate a micron-sized liquid spherical resonator and present an approximated solution for the resonator interface deformation due to the radiation pressure. We then derive an analytical approach that can exactly calculate the droplet deformation induced by the radiation pressure. The accuracy of the analytical solution is confirmed through numerical analyses based on the boundary element method. We show that the nonlinear optofluidic effect induced by the radiation pressure is stronger than the Kerr effect and the thermal effect under a large variety of realistic conditions. Using liquids with ultra-low and experimentally attainable interfacial tension, we further confirm the prediction that it may only take a few photons to produce measurable WGM resonance shift through radiation pressure induced droplet deformation. Similar to the radiation pressure, the scattering force in the droplet can induce a rotational fluid motion which also leads to the interface deformation. The interface deformation can also be produced by the thermocapillarity as a result of the WGM energy absorption and temperature increase. In this study, we provide a numerical scheme to calculate the fluid motion and quantify the nonlinearity induced by the optical scattering force and thermocapillarity. The magnitude of the optofluidic nonlinearities induced by the radiation pressure, thermocapillary effect, light scattering and Kerr effect are compared. We show that the radiation pressure due to the WGM produces the strongest nonlinear optofluidic effect. / Ph. D.

Surfaces/interfaces are considered as one of the key factors that determine performance, and ultimately the application, of materials. In many cases, surface/interface modifications are required for desired properties, such as adhesion and wettability. Organosilanes have been widely used to alter surface/interfacial properties for many materials including metals, glass, and polymers, etc. However, controllable processes for surface/interfacial modification are desired. This thesis aims to explore controllable paths for surface/interfacial modifications on siloxane or hydrocarbon-based materials using organosilanes. Further understanding about the methodologies for quantification of functional groups located at surfaces/interfaces is also within the scope of this thesis. In this thesis, a comprehensive study of PDMS surface modification using thioalkylsilane coupling agents is described. An equilibrium silanization allowed the introduction of thiols on silicone elastomer surfaces under control and without damaging the surface. Two different titration methods for testing thiols in solution were developed and improved for quantification of thiol groups located at air-solid interfaces. The thiol-functionalized silicone could be further modified with maleic anhydride and/or with a variety of polymers and surfactants in a single step or two steps. A long term, stable hydrophilic surface was obtained after these modifications. In this thesis, the modification of hydrocarbon-based materials is also described. A method based on the Piers-Rubinsztajn reaction was used to convert lignin into value-added chemicals, including monomeric/oligomeric aromatics and lignin composites. For the hard wood lignin, reduction of the ether bonds and silylation with hydrosilanes led to nearly complete fragmentation. The monomeric/oligomeric aromatics decomposed from hard wood lignin are easy to process as demonstrated by their excellent solubility in various solvents. Alternatively, softwood, which does not have an ideal structure for fragmentation, is effectively employed as “green filler” in silicones for lignin-based elastomer/foams. The partial (interfacial) reduction of hydrosilanes at lignin interfaces results in covalent linkage sbetween lignin and siloxane network, improving the interfacial miscibility. The softwood lignin, thus plays dual roles as a crosslinking and reinforcing agent. Formulations were readily developed to prepare silicone foams/elastomers by controlling processing parameters and methods. Lignin-based silicone elastomers could be obtained with additional solvent and casting in an open mold; lignin-based silicone foams could be molded in a volume-confined mold after extrusion. / Thesis / Doctor of Philosophy (PhD)

Structural characterization is essential to understand the formation mechanisms of the nanostructures in thin absorber layers in third generation solar cells and amyloid protein aggregates. Since to the dimension of the precipitated structures is in nanometer scale, electron tomography technique in transmission electron microscopy (TEM) has been applied as a major tool to analyze the 3D order and distribution of precipitates using the electron tomography technique.  Silicon rich silicon carbide (SRSC) films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique and annealed in the nitrogen atmosphere for 1 hour at 1100 °C. The spectrum-imaging (SI) technique in Energy filtered TEM (EFTEM) imaging mode was used to develop electron tomography. From the reconstructed sub-volumes, the complex, three dimensional interfacial nanostructure between the precipitated NPs and their parental matrix was observed and explained in terms of thermodynamic concepts. Additionally, the feasibility of raw data 4D electron tomography has been demonstrated using the EFTEM SI dataset. The aggregation process of the human islet amyloid polypeptide (hIAPP) has a great impact on human health. In this thesis, a model system has been taken to study the ultrastructure of the hIAPP aggregates that are present in the fat body tissue surrounding the brain of Drosophila melanogaster. Electron tomography technique on TEM revealed clear crystalline structures in 3D. For the first time, the presence of a 5-fold twinned structure in biology was discovered. An intriguing finding is the filament like interconnection of hIAPP protein granules observed predominantly along the nearest neighbor directions. This suggests the existence of the directional binding forces between two nearest protein granules in addition to dipole-dipole interactions.

The self-assembly behavior of arborescent polystyrene-<em>graft</em>-poly(ethylene oxide) copolymers (PS-<em>g</em>-PEO) at the air-water interface and the solubilization/release properties of arborescent polystyrene-<em>graft</em>-poly(2-vinylpyridine) (PS-<em>g</em>-P2VP) copolymers were investigated. These amphiphilic dendritic molecules are covalently bonded unimolecular micelles incorporating a highly branched hydrophobic polystyrene core surrounded by a hydrophilic poly(ethylene oxide) or poly(2-vinylpyridine) shell. Molecules of PS-<em>g</em>-PEO copolymers spontaneously formed supramolecular assemblies at the air-water interface. The type of superstructures formed was found to depend upon copolymer composition, while the level of association was more directly related to the branching density of the polymers. At low surface pressures the PEO segments apparently remained adsorbed on the water subphase, but desorbed into water at very high surface pressures, in the condensed monolayer state. Controlled degradation of the PEO chains with UV light greatly enhanced molecular association, resulting in the formation of either large clusters or long ribbon-like superstructures. The PS-<em>g</em>-P2VP copolymers were found to efficiently solubilize and release hydrophobic small molecules in aqueous media. The partition coefficient and solubilization capacity of the copolymers for hydrophobic polyaromatic hydrocarbons increased with the polystyrene content of the copolymers, while the rate of solubilization decreased with increasing branching functionality of the copolymers. The release profiles for two model drugs displayed an initial burst in release followed by gradual approach to equilibrium. The diffusion coefficients of the drugs in the micelles increased with the branching functionality and the generation number of the micelles, presumably due to increased electrostatic repulsions of the protonated vinylpyridine units.

No description available.

The objective of this research work was to develop a methodology for experimentally estimating the interfacial properties at slag-metal interfaces. From previous experiments carried out in the division, it was decided to use surface active elements like sulfur or oxygen to trace any motion at the interface. For this purpose the following experimental investigations were carried out. Firstly the density of slag was estimated using the Archimedes Principle and the Sessile Drop technique. The density of the slag would give the molten slag height required for the surface active element to travel before reaching the slag-metal interface. Diffusivity measurements were uniquely designed in order to estimate the sulfur diffusion through slag media. It was for the first time that the chemical diffusivity was estimated from the concentration in the metal phase. Experiments carried out validated the models developed earlier. The density and diffusivity value of sulfur in the slag was used to accurately capture the time for sulfur to reach the slag-metal interface. The oscillations were identified by calculating the contact angle variations and the interfacial velocity was estimated from the change in the surface area of the liquid iron drop. The interfacial tension was estimated from the contact angles and the interfacial dilatational modulus was calculated. Based on cold model experiments using water as well as mercury, an equation of the dependence of the interfacial shear viscosity on the interfacial velocity and interfacial tension was established. This paved way for the estimation of the interfacial shear viscosity at the slag-metal interface. The present study is expected to have a strong impact on refining reactions in pyometallurgical industries where slag/metal interfaces play an important role. From a fundamental view point, this provides a deeper insight into interfacial phenomena and presents an experimental technique to quantify the same. / QC 20101130