An anti-reflective (AR) lens is an ultrathin multilayered structure composing of AR coatings on a lens substrate. These coatings can be made by a spin-coating process with a nanocomposite of UV curable acrylic monomers and well dispersed metal oxide nanoparticles. The in-situ UV polymerization rate was reduced by oxygen inhibition and the absorption of UV energy by the metal oxide nanoparticles. There are few studies of the mechanical properties of ultrathin polymeric coatings that include the effects of substrates, the viscoelastic behaviors of polymers in submicron scales and the effects of multilayered coatings. With a coating system based on UV cured dipentaerythritol pentaacrylate on silicon wafer substrates, nanoindentation tests showed that the nominal reduced contact modulus increased with the indentation load and penetration depth due to the effect of the substrate, in quantitative agreement with an elastic contact model. Ultrathin polymeric coatings subjected to constant indentation loads exhibit shear-thinning during flow. None of the models examined completely described the elastic response of an ultrathin polymeric coating on a compliant plastic substrate. The effective modulus was a function of coating-substrate property, indenter tip size, coating thickness, adhesion and residual stress. It was logarithmic dependent on the ratio of the indentation depth to the coating thickness prior to coating fracture. An elastic model, assuming shear-lag and a plane-stress state, was used to estimate the interfacial strength between a submicron coating and a compliant substrate. The critical indentation load for the indentation-induced delamination of the coating from the substrate increased with the third power of the indentation depth and was a linear function of the reciprocal of the coating thickness. The interfacial strength was 70.4 MPa. Mechanical properties and fracture characteristics of CVD ceramic and nanocomposite coatings on polymer substrates were evaluated by nanoindentation and nanoscratching tests. The AR lenses made with polymer nanocomposite coatings have better mechanical properties due to the close match of properties between the coatings and the plastic substrate. The new approach to making AR lenses with polymer nanocomposites on plastic substrate is promising.

Surfactant flooding in carbonate matrix acidizing treatment has been widely used for changing the wettability of the rock and to achieve low IFT values. Optimizing the type of surfactant and concentration for the specific oil field is very important in order to avoid formation damage and to reduce the treatment cost. We built an experimental procedure for screening the right surfactant to alter the wettability and aid in acidizing of Pekisko formation, Canada, which is strongly oil-wet and has high viscosity oil. Five surfactants were tested out of which three are cationic, one amphoteric and the other one was a fluoro-surfactant. Measurements were made of interfacial tension with different surfactant types/concentrations in brine with the oil and xylene, critical micelle concentration of each surfactant, solubility characteristics of the surfactants, compatibility of the chemical additives, wettability of the core after treating with surfactants, and core flooding in the laboratory to simulate matrix acidizing. From the results obtained we noted that the fluoro-surfactant can cause formation damage due to precipitation in the brine. So the compatibility of every chemical additive should be tested first. The use of xylene as a pre-flush solution lowered the CMC and hence reduced the cost of the surfactant treatment. Aromox, an amine based surfactant was best suited for matrix acidizing treatment of the Pekisko formation.

The performance of smart structures depends on the dynamic electromechanical behavior of piezoelectric sensors/actuators and the bonding condition along the interface. This thesis contents a theoretical study of the coupled electromechanical characteristics of a surface-bonded piezoelectric sensor with interfacial debonding, which is subjected to high frequency mechanical loads. A one dimensional sensor model is proposed. Analytical solutions based on the integral equation method are provided. Numerical simulation is conducted to evaluate the effects of different parameters upon the dynamic load transfer between the sensor and the host medium. The results indicate that, the material combination, the sensor geometry, and the loading frequency, affect the load transfer significantly. The analytical solution of the elastic wave field in the host medium is obtained and used to evaluate the effects of different parameters upon the resulting wave field. The theoretical solution demonstrates the basic properties of wave propagation under current loading conditions.

Nanoscale materials behave differently than their bulk counterparts due, in part, to the reduced length scales and the increased surface to core atom ratio. As the length scales decrease, the surface atoms become increasingly important as they make up a larger percentage of the total number of atoms. These surface atoms have magnetic properties that differ from the core atoms due to a surface anisotropy that alters the interparticle, intraparticle, and exchange interactions. In this work, we have synthesized three different nanoscale systems that will allow us to explore the physics of the different interactions. Cu/gamma-Fe2O3 core/shell nanoparticles were chosen because the gamma-Fe2O3 cores have vacancies in their B-sites, broken coordination at the surface, and experience superexchange interactions. As a comparison, multiphase undoped and V-doped SiO2/FeCo nanoparticles were chosen as these nanoparticles do not suffer from vacancies or surface disorder and experience both direct exchange interactions from the nanoparticle core and superexchange interactions between the FeCo core and the metal silicate interfacial phase. Finally, Fe nanocrystallites were grown in a Cu matrix as they present no vacancies or surface disorder, and they are single phase. We observed that the interfacial phases that form in these core/shell and nanocrystallite/matrix nanoscale systems alters significantly the physics of the magnetism. The overall magnetic properties, the elemental magnetism, and the atomic magnetism were all observed to be altered by this interfacial phase, along with the interparticle and intraparticle interactions. In addition, the thickness of this interfacial phase, and thus the strength of its affect, was controlled by controlling the thickness of the shells or the amount of intermixing in the case of the nanostructured thin film. / February 2016

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2016-10-06T18:36:32Z No. of bitstreams: 1 DissCMC.pdf: 3606303 bytes, checksum: 03bf7fccc7e73860758575867e0742ed (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-14T14:17:05Z (GMT) No. of bitstreams: 1 DissCMC.pdf: 3606303 bytes, checksum: 03bf7fccc7e73860758575867e0742ed (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-14T14:17:14Z (GMT) No. of bitstreams: 1 DissCMC.pdf: 3606303 bytes, checksum: 03bf7fccc7e73860758575867e0742ed (MD5) / Made available in DSpace on 2016-10-14T14:17:24Z (GMT). No. of bitstreams: 1 DissCMC.pdf: 3606303 bytes, checksum: 03bf7fccc7e73860758575867e0742ed (MD5) Previous issue date: 2016-04-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The fabrics are derived from fibers, which are divided into to main groups: natural (like cotton) and chemical (such as rayon and polyester). In the processing of the fabric, drying is a major operation, contributing to the finishing and obtaining a fabric with greater brightness and also better touch. However, each tissue has a different structure and different composition which can influence its absorption capacity and retention of water. The aim of this study is to analyze the drying of 3 types of fabrics (polyester, toweling and jeans), and evaluate how the material characteristics and operating conditions influence the process. Experimental tests were conducted in oven with natural convection, with natural convection, at temperatures of 50, 60 and 70 ° C and also in a tunnel dryer with forced convection under the conditions of 1.0 and 2.0 m / s at the temperatures of 50, 60 and 70 ° C. Besides that, the adjustments of generalized curves of drying were evaluated, there are empirical equations of kinetics. In the evaluation of water absorption in saturated atmosphere at 40 to 60 ° C, it was observed that the polyester is the fabric that absorbs less water while the jeans had greater absorption capacity. It was also found that absorption increases with increasing temperature for all three fabrics. By analyzing the influence of operating conditions on the drying fabrics, the air speed was the variable that most influenced the moisture reduction, indicating that surface resistance was the limiting mechanism in drying. Page model (1949), was the most appropriate to represent the generalized kinetic curves for the fabrics evaluated.The comparative analysis of the fabrics showed that, although significant differences in the type of fiber and fabric structure, these characteristics do not influence the drying of the material, indicating that the drying of materials with high surface area, the process is controlled by the conditions flow. / Os tecidos são originados a partir de fibras têxteis, a quais são divididas em grandes grupos: naturais (como o algodão) e químicas (como o rayon e o poliéster ). No beneficiamento dos tecidos, a secagem é uma operação primordial, que contribui para o acabamento final e obtenção de um tecido com maior brilho e também melhor toque. Porém cada tipo de tecido possui características de estrutura e composição diferentes, o que pode influenciar sua capacidade de absorção e retenção de água. O objetivo deste trabalho foi analisar a secagem de tipos de tecidos (poliéster, atoalhado e jeans), e avaliar como as características dos materiais e as condições operacionais influenciam no processo. Os ensaios experimentais foram conduzidos em estufa com convecção natural, nas temperaturas de 50, 60 e 70 °C e também em secador de túnel com convecção forçada, nas condições de 1,0 e 2,0 m/s e temperaturas de 50, 60 e 70 °C. Além disso, foram avaliados os ajustes das curvas generalizadas de secagem, à equações empíricas de cinética. Na avaliação da absorção de água em atmosfera saturada a 40 e 60 oC, observou-se que o poliéster é o tecido que menos absorve água, enquanto o jeans apresentou maior capacidade de absorção. Constatou-se também que a absorção aumenta com o aumento da temperatura, para os três tipos de tecidos. Ao analisar a influência das condições operacionais na secagem dos tecidos, a velocidade do ar foi a variável que apresentou maior influência na redução de umidade, indicando que resistência superficial foi o mecanismo limitante na secagem. O modelo de Page (1949), foi o mais apropriado para representar as curvas de cinéticas generalizadas para os tecidos avaliados. A análise comparativa entre os tecidos mostrou que, apesar das diferenças significativas no tipo de fibra e estrutura do tecido, estas características não influenciaram a secagem do material, indicando que, na secagem de materiais com elevada área superficial, o processo é controlado pelas condições de escoamento.

The gas-absorption/chemical-reaction (GACR) method used in chemical engineering to quantify gas-liquid interfacial area in reactor systems is adapted for the first time to measure the effective air-water interfacial area of natural porous media. Experiments were conducted with the GACR method, and two standard methods (X-ray microtomographic imaging and interfacial partitioning tracer tests) for comparison, using model glass beads and a natural sand. The results of a series of experiments conducted under identical conditions demonstrated that the GACR method exhibited excellent repeatability for measurement of interfacial area (A(ia)). Coefficients of variation for A(ia) were 3.5% for the glass beads and 11% for the sand. Extrapolated maximum interfacial areas (A(m)) obtained with the GACR method were statistically identical to independent measures of the specific solid surface areas of the media. For example, the A(m) for the glass beads is 29 (1) cm(-1), compared to 32 (3), 30 (2), and 31 (2) cm(-1) determined from geometric calculation, N2/BET measurement, and microtomographic measurement, respectively. This indicates that the method produced accurate measures of interfacial area. Interfacial areas determined with the GACR method were similar to those obtained with the standard methods. For example, A(ia)s of 47 and 44 cm(-1) were measured with the GACR and XMT methods, respectively, for the sand at a water saturation of 0.57. The results of the study indicate that the GACR method is a viable alternative for measuring air-water interfacial areas. The method is relatively quick, inexpensive, and requires no specialized instrumentation compared to the standard methods.

The anomalous Hall effect (AHE) has been discovered for over a century, but its origin is still highly controversial theoretically and experimentally. In this study, we investigated the scattering effect on the AHE for both exploring the underlying physics and technical applications. We prepared Cox(MgO)100-x granular thin films with different Co volume fraction (34≤x≤100) and studied the interfacial scattering effect on the AHE. The STEM HAADF images confirmed the inhomogeneous granular structure of the samples. As x decreases from 100 to 34, the values of longitudinal resistivity (pxx) and anomalous Hall resistivity (pAHE) respectively increase by about four and three orders in magnitude. The linear scaling relation between the anomalous Hall coefficient (Rs) and the pxx measured at 5 K holds in both the as-prepared and annealed samples, which suggests a skew scattering dominated mechanism in Cox(MgO)100-x granular thin films. We prepared (Fe36/n/Au12/n)n, (Ni36/n/Au12/n)n and (Ta12/n/Fe36/n)n multilayers to study the interfacial scattering effect on the AHE. The multilayer structures were characterized by the XRR spectra and TEM images of cross-sections. For the three serials of multilayers, both the pxx and pAHE increase with n, which clearly shows interfacial scattering effect. The intrinsic contribution decreases with n increases in the three serials of samples, which may be due to the crystallinity decaying or the finite size effect. In the (Fe36/n/Au12/n)n samples, the side-jump contribution increases with nn, which suggests an interfacial scattering-enhanced side jump. In the (Ni36/n/Au12/n)n samples, the side-jump contribution decreases with n increases, which could be explained by the opposite sign of the interfacial scattering and grain boundary scattering contributed side jump. In the (Ta12/n/Fe36/n)n multilayers, the side-jump contribution changed from negative to positive, which is also because of the opposite sign of the interfacial scattering and grain boundary scattering contributed side jump. The interfacial scattering effect on the AHE is much more complicated than surface scattering in thin films or scattering by delta-impurities in bulk-like samples.

Improving the formability and crashworthiness of wrought magnesium alloys are the two biggest challenges in current magnesium technology. Magnesium is the best material candidate for enabling required improvements in fuel economy of combustion engines and increases in ranges of electric vehicles. In hexagonal closed-packed (HCP) structures, effects of grain size/morphology and crystallographic texture are particularly important. Prior research has established a general understanding of the dependences of strength and strain anisotropy on grain morphology and texture. Unfortunately, deformation, recrystallization, and grain growth strategies that control the microstructures and textures of cubic metals and alloys have not generally worked for HCPs. For example, in Magnesium, the deformation texture induced by primary forming operations (rolling, extrusion, etc.) is not randomized by recrystallization and may strengthen during grain growth. A strong texture reduces formability during secondary forming (stamping, bending, hemming etc.) Thus, the inability to randomize texture has impeded the implementation of magnesium alloys in engineering applications. When rare earth solutes are added to magnesium alloys, distinct new textures are derived. However, rare earth texture derivation remains insufficiently explained. Currently, it is hypothesized that unknown mechanisms of alloy processing are at work, arising from the effects of grain boundary intrinsic defect structures on microstructural evolution. This dissertation is a comprehensive attempt to identify formal methodologies of analyzing the behavior of grain boundaries in magnesium. We focus particularly on twin boundaries and asymmetric tilt grain boundaries using molecular dynamics. We begin by exploring twin nucleation in magnesium single crystals, elucidating effects of heterogeneities on twin nucleation and their relationships with concurrent slip. These efforts highlighted the necessity of imperfections to nucleate {10-12} twins. Subsequent studies encountered the importance of deformation faceting on the high mobility of {10- 12} and stabilization of observed twin mode boundaries. Implementation of interfacial defect theory was necessary to decipher the complex mechanisms observed which govern the development of defects in grain boundaries, disconnection pile-up, facet nucleation, interfacial disclination nucleation, disconnection movements, disconnection transformation across interfacial disclinations, crossaceting, and byproducts of interactions between lattice dislocations and grain boundaries.

No description available.

No / This report covers experimental studies and numerical modelling of interfacial instability in the bi-layer coextrusion flow of two low-density polyethylene melts. Melt streams are converged at an angle of 30° to a common die land. Melt stream confluence was observed in two coextrusion die arrangements. In one die design, which we term ‘bifurcated’ the melt stream is split by a divider plate in the die after being delivered from a single extruder. In the other design melt streams are delivered to a die from two separate extruders. In each die design melt flow in the confluent region and die land to the die exit was observed through side windows of a visualization cell. Velocity ratios of the two melt streams were varied and layer thickness ratios producing wave type interfacial instability determined for each melt for a variety of flow conditions. Stress and velocity fields in the coextrusion arrangements were quantified using stress birefringence and particle image velocimetry techniques. Wave type interfacial instability occurred in the processing of the low-density polyethylene melts at specific, repeatable, stream layer ratios. The birefringent pattern in the confluence region and the beginning of the die land appeared stable even when the extrudate exhibited instability. However, disturbances were observed in the flow field near the exit of the die land. The study demonstrates conclusively it is possible for interfacial instability to occur in the coextrusion of the same melt. The study also shows that wave type interfacial instability in the coextrusion process is not caused by process perturbations of extruder screw rotation. Increased melt elasticity appears to promote this type of instability. A modified Leonov model and Flow 2000™ software was used to simulate the LDPE melt flows through these geometries. There was reasonable agreement between modelled at experimentally determined stress fields. Modelling however provided far more detailed stress gradient information than could be resolved from the optical techniques. A total normal stress difference (TNSD) sign criterion was used to predict the critical layer ratio for the onset of the interfacial instability in one die arrangement and good agreement between theory and experiment has been obtained.