Numerical simulation of the liquid phase in SnO(2) thin film deposition by sol-gel-dip-coating

The fluid flow of the liquid phase in the sol-gel-dip-coating process for SnO(2) thin film deposition is numerically simulated. This calculation yields useful information on the velocity distribution close to the substrate, where the film is deposited. The fluid modeling is done by assuming Newtonian behavior, since the linear relation between shear stress and velocity gradient is observed. Besides, very low viscosities are used. The fluid governing equations are the Navier-Stokes in the two dimensional form, discretized by the finite difference technique. Results of optical transmittance and X-ray diffraction on films obtained from colloidal suspensions with regular viscosity, confirm the substrate base as the thickest part of the film, as inferred from the numerical simulation. In addition, as the viscosity increases, the fluid acquires more uniform velocity distribution close to the substrate, leading to more homogenous and uniform films.

Numerical simulation of the liquid phase in SnO2 thin film deposition by sol-gel-dip-coating

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

AN ACTINOMETRIC STUDY OF C2H2 PLASMA POLYMERIZATION AND FILM PROPERTIES

Thin polymer films were grown in radio frequency discharges containing C2H2. Actinometry revealed the trend in the plasma concentration of the CH species as a function of the operating pressure. The C-H bond density in the films, revealed by infrared analysis, was found to increase with the pressure of C2H2 in a similar way to that of the concentration of the CH species in the discharge. From transmission ultraviolet-visible spectroscopy data, optical parameters of the polymers, namely, the refractive index and the optical gap, were calculated. For the range of pressure studied, the refractive index decreased from 1.73 to 1.63 and the optical gap increased from 2.4 to 3.3 eV. Finally, measurements of the residual stress of the polymer films were carried out by the bending beam method, using a He-Ne laser, yielding values from 0.05 to 0.3 GPa. (C) 1995 American Vacuum Society.

Evaluating the residual stress in PbTiO3 thin films prepared by a polymeric chemical method

We report a study of residual stress in PbTiO3 (PT) thin films prepared on Si substrates by a polymeric chemical method. The E(1TO) frequency was used to evaluate the residual stress through an empirical equation available for bulk PT. We find that the residual stress in PT films increases as the film thickness decreases and conclude that it originates essentially from the contributions of extrinsic and intrinsic factors. Polarized Raman experiments showed that the PT films prepared by a polymeric chemical method are somewhat a-domain (polar axis c parallel to the substrate) oriented.

Piezoelectric composite film for acoustic emission detection

The continuous technological advances require materials with properties that conventional material cannot display. Material property combinations are being the focus to the development of composite materials, which are considered a multiphase material that exhibits properties of the constituent phases. One interesting material to be studied as sensing material is the composite made of ferroelectric ceramic and polymeric matrix as a two-phases composite material. In that case, the combinations properties intended are the high piezo and pyroelectric activities of the dense ceramic with the impact resistance, flexibility, formability and low densities of the polymer. Using the piezoelectric property of the composite film, it can be used to detect acoustic emission (AE), which is a transient elastic wave generated by sudden deformation in materials under stress. AE can be applied for evaluating the health of structures in a nondestructive way and without any lapse of time. The preliminary result indicates that the composite Pz34/PEEK can be used as sensing material for nondestructive evaluation. ©2009 IEEE.

Nanoscale insight into the statics and dynamics of polarization behavior in thin film ferroelectric capacitors

In this study, we review recent advances in PFM studies of micrometer scale ferroelectric capacitors, summarize the experimental PFM-based approach to investigation of fast switching processes, illustrate what information can be obtained from PFM experiments on domains kinetics, and delineate the scaling effect on polarization reversal mechanism. Particular attention is given to PFM studies of mechanical stress effect on polarization stability.

Diametral tensile strength and film thickness of an experimental dental luting agent derived from castor oil

The need to develop new dental luting agents in order to improve the success of treatments has greatly motivated research. Objective: The aim of this study was to evaluate the diametral tensile strength (DTS) and film thickness (FT) of an experimental dental luting agent derived from castor oil (COP) with or without addition of different quantities of filler (calcium carbonate - CaCO3). Material and Methods: Eighty specimens were manufactured (DTS N=40; FT N=40) and divided into 4 groups: Pure COP; COP 10%; COP 50% and zinc phosphate (control). The cements were mixed according to the manufacturers' recommendations and submitted to the tests. The DTS test was performed in the MTS 810 testing machine (10 KN, 0.5 mm/min). For FT test, the cements were sandwiched between two glass plates (2 cm(2)) and a load of 15 kg was applied vertically on the top of the specimen for 10 min. The data were analyzed by means of one-way ANOVA and Tukey's test (alpha=0.05). Results: The values of DTS (MPa) were: Pure COP- 10.94 +/- 1.30; COP 10%- 30.06 +/- 0.64; COP 50%- 29.87 +/- 0.27; zinc phosphate- 4.88 +/- 0.96. The values of FT (pm) were: Pure COP- 31.09 +/- 3.16; COP 10%- 17.05 +/- 4.83; COP 50%- 13.03 +/- 4.83; Zinc Phosphate- 20.00 +/- 0.12. One-way ANOVA showed statistically significant differences among the groups (DTS - p=1.01E-40; FT - p=2.4E-10). Conclusion: The experimental dental luting agent with 50% of filler showed the best diametral tensile strength and film thickness.

Sviluppo e validazione di un modello di film fluido per simulazioni CFD di motori a combustione interna

A wall film model has been implemented in a customized version of KIVA code developed at University of Bologna. Under the hypothesis of `thin laminar ow' the model simulates the dynamics of a liquid wall film generated by impinging sprays. Particular care has been taken in numerical implementation of the model. The major phenomena taken into account in the present model are: wall film formation by impinging spray; body forces, such as gravity or acceleration of the wall; shear stress at the interface with the gas and no slip condition on the wall; momentum contribution and dynamic pressure generated by the tangential and normal component of the impinging drops; film evaporation by heat exchange with wall and surrounding gas. The model doesn't consider the effect of the wavy film motion and suppose that all the impinging droplets adhere to the film. The governing equations have been integrated in space by using a finite volume approach with a first order upwind differencing scheme and they have been integrated in time with a fully explicit method. The model is validated using two different test cases reproducing PFI gasoline and DI Diesel engine wall film conditions.

Stress – structure correlations in grafted polymer films

In der vorliegenden Arbeit wurden experimentelle Untersuchungen zu gepfropften Polymerfilmen durchgeführt. Dabei wurden endgepfropfte poly-methyl-methacrylate (PMMA) Bürsten hergestellt durch „grafting from“ Methoden und polystyrol (PS)/ poly-vinyl-methyl-ether (PVME) Polymerfilme gepfropft auf UV sensitiven Oberflächen untersucht. Zur Strukturuntersuchung wurden die hergestellten Systeme wurden mit Rasterkraftmikroskopie (engl.: Surface Probe Microscopy, SPM), Röntgen - und Neutronenreflektivitätsmessungen, sowie mit Röntgenstreuung unter streifenden Einfall (engl.: Grazing Incidence Small Angle X-Ray Scattering, GISAXS) untersucht. rnEs wurde gezeigt, dass ein aus der Transmissionsstreuung bekanntes Model auch für auch für die GISAXS Analyse polydisperser Polymerdomänen und Kolloidsysteme verwendet werden kann. Der maximale Fehler durch die gemachten Näherungen wurde auf < 20% abgeschätzt.rnErgebnisse aus der Strukturanalyse wurden mit mechanischen Filmeigenschaften verknüpft. Dazu wurden mechanische Spannungsexperimente durchgeführt. Hierzu wurden die zu untersuchenden Filme selektiv auf einzelne Mikro-Federbalken-Sensoren (engl.: Micro Cantilever Sensor, MCS) der MCS Arrays aufgebracht. Dies wurde durch Maskierungstechniken und Mikro-Kontaktdrucken bewerkstelligt. rnPhasenübergansexperimente der gepfropften PS/PVME Filme haben gezeigt, dass die Möglichkeit einer Polymer/Polymer Phasenseparation stark von Propfpunktdichte der gebundenen Polymerketten mit der Oberfläche abhängt. PS/PVME Filmsysteme mit hohen Pfropfpunktdichten zeigten keinen Phasenübergang. Bei niedrig gepfropften Filmsystemen waren hingegen Polymer/Polymer Phasenseparationen zu beobachten. Es wurde geschlussfolgert, dass die gepfropften Polymersysteme einen hinreichenden Grad an entropischen Freiheitsgraden benötigen um eine Phasenseparation zu zeigen. Mechanische Spannungsexperimente haben dabei das Verstehen der Phasenseparationsmechanismen möglich gemacht.rnAus Quellexperimenten dichtgepfropfter PMMA Bürsten, wurden Lösungsmittel-Polymer Wechselwirkungsparameter (-Parameter) bestimmt. Dabei wurde festgestellt, dass sich die erhaltenen Parameter aufgrund von Filmbenetzung und entropischen Effekten maßgeblich von den errechneten Bulkwerten unterscheiden. Weiterhin wurden nicht reversible Kettenverschlaufungseffekt beobachtet.

Stress & structure of thin polymer brush films

Polymer brushes have unique properties with a large variety of possible applications ranging from responsive coatings and drug delivery to lubrication and sensing. For further development a detailed understanding of the properties is needed. Established characterization methods, however, only supply information of the surface. Experimental data about the inner “bulk” structure of polymer brushes is still missing.rnScattering methods under grazing incidence supply structural information of surfaces as well as structures beneath it. Nanomechanical cantilevers supply stress data, which is giving information about the forces acting inside the polymer brush film. In this thesis these two techniques are further developed and used to deepen the understanding of polymer brushes. rnThe experimental work is divided into four chapters. Chapter 2 deals with the preparation of polymer brushes on top of nanomechanical cantilever sensors as well as large area sample by using a “grafting-to” technique. The further development of nanomechanical cantilever readout is subject of chapter 3. In order to simplify cantilever sensing, a method is investigated which allows one to perform multiple bending experiments on top of a single cantilever. To do so, a way to correlate different curvatures is introduced as well as a way to conveniently locate differently coated segments. In chapter 4 the change in structure upon solvent treatment of mixed polymer brushes is investigated by using scattering methods and nanomechanical cantilevers amongst others. This allows one to explain the domain memory effect, which is typically found in such systems. Chapter 5 describes the implementation of a phase shifting interferometer - used for readout of nanomechanical cantilevers - into the µ-focused scattering beamline BW4, allowing simultaneous measurements of stress and structure information. The last experimental chapter 6 deals with the roughness correlation in polymer brushes and its dependence on the chain tethered density.rnIn summary, the thesis deals with utilization of new experimental techniques for the investigation of polymer brushes and further development of the techniques themselves.rn

Numerical modeling of the failure mechanisms in Si thin film anode for Li-ion batteries

In recent times, the demand for the storage of electrical energy has grown rapidly for both static applications and the portable electronics enforcing the substantial improvement in battery systems, and Li-ion batteries have been proven to have maximum energy storage density in all rechargeable batteries. However, major breakthroughs are required to consummate the requirement of higher energy density with lower cost to penetrate new markets. Graphite anode having limited capacity has become a bottle neck in the process of developing next generation batteries and can be replaced by higher capacity metals such as Silicon. In the present study we are focusing on the mechanical behavior of the Si-thin film anode under various operating conditions. A numerical model is developed to simulate the intercalation induced stress and the failure mechanism of the complex anode structure. Effect of the various physical phenomena such as diffusion induced stress, plasticity and the crack propagation are investigated to predict better performance parameters for improved design.

Study of carbon nanotube film and shape memory alloys treatment for sensing and structural vibration control

Structural vibration control is of great importance. Current active and passive vibration control strategies usually employ individual elements to fulfill this task, such as viscoelastic patches for providing damping, transducers for picking up signals and actuators for inputting actuating forces. The goal of this dissertation work is to design, manufacture, investigate and apply a new type of multifunctional composite material for structural vibration control. This new composite, which is based on multi-walled carbon nanotube (MWCNT) film, is potentially to function as free layer damping treatment and strain sensor simultaneously. That is, the new material integrates the transducer and the damping patch into one element. The multifunctional composite was prepared by sandwiching the MWCNT film between two adhesive layers. Static sensing test indicated that the MWCNT film sensor resistance changes almost linearly with the applied load. Sensor sensitivity factors were comparable to those of the foil strain gauges. Dynamic test indicated that the MWCNT film sensor can outperform the foil strain gage in high frequency ranges. Temperature test indicated the MWCNT sensor had good temperature stability over the range of 237 K-363 K. The Young’s modulus and shear modulus of the MWCNT film composite were acquired by nanoindentation test and direct shear test, respectively. A free vibration damping test indicated that the MWCNT composite sensor can also provide good damping without adding excessive weight to the base structure. A new model for sandwich structural vibration control was then proposed. In this new configuration, a cantilever beam covered with MWCNT composite on top and one layer of shape memory alloy (SMA) on the bottom was used to illustrate this concept. The MWCNT composite simultaneously serves as free layer damping and strain sensor, and the SMA acts as actuator. Simple on-off controller was designed for controlling the temperature of the SMA so as to control the SMA recovery stress as input and the system stiffness. Both free and forced vibrations were analyzed. Simulation work showed that this new configuration for sandwich structural vibration control was successful especially for low frequency system.

Intergranular Corrosion and Stress Corrosion Cracking of Extruded AA6005A

A research program focused on understanding the intergranular corrosion (IGC) and stress corrosion cracking (SCC) behavior of AA6005A aluminum extrusions is presented in this dissertation. The relationship between IGC and SCC susceptibility and the mechanisms of SCC in AA6005A extrusions were studied by examining two primary hypotheses. IGC susceptibility of the elongated grain structure in AA6005A exposed to low pH saltwater was found to depend primarily on the morphology of Cu-containing precipitates adjacent to the grain boundaries in the elongated grain structure. IGC susceptibility was observed when a continuous (or semi-continuous) film of Cu-containing phase was present along the grain boundaries. When this film coarsened to form discrete Cu-rich precipitates, no IGC was observed. The morphology of the Cu-rich phase depended on post-extrusion heat treatment. The rate of IGC penetration in the elongated grain structure of AA6005A-T4 and AA6005A-T6 extrusions was found to be anisotropic with IGC propagating most rapidly along the extrusion direction, and least rapidly along the through thickness direction. A simple 3-dimensional geometric model of the elongated grain structure was accurately described the observed IGC anisotropy, therefore it was concluded that the anisotropic IGC susceptibility in the elongated grain structure was primarily due to geometric elongation of the grains. The velocity of IGC penetration along all directions in AA6005A-T6 decreased with exposure time. Characterization of the local environment within simulated corrosion paths revealed that a pH gradient existed between the tip of the IGC path and the external environment. Knowledge of the local environment within an IGC path allowed development of a simple model based on Fick's first law that considered diffusion of Al3+ away from the tip of the IGC path. The predicted IGC velocity agreed well with the observed IGC velocity, therefore it was determined that diffusion of Al3+ was the primary factor in determining the velocity of IGC penetration. The velocity of crack growth in compact tensile (CT) specimens of AA6005A-T6 extrusion exposed to 3.5% NaCl at pH = 1.5 was nearly constant over a range of applied stress intensities, exposure times, and crack lengths. The crack growth behavior of CT specimens of AA6005A-T6 extrusion exposed to a solution of 3.5% NaCl at pH = 2.0 exhibited similar behavior, but the crack velocity was ~10.5X smaller than that those exposed to a solution at pH =1.5. Analysis of the local stress state and polarization behavior at the crack tip predicted that increasing the pH of the bulk solution from 1.5 to 2.0 would decrease the corrosion current density at the crack tip by approximately 11.8X. This predicted decrease in corrosion current density was in reasonable agreement with the observed decrease in SCC velocity associated with increasing the solution pH from 1.5 to 2.0. The agreement between the predicted and observed SCC velocities suggested that the electrochemical reactions controlling SCC in AA6005A-T6 extrusions are ultimately controlled by the pH gradient that exists between the crack tip and external environment.

Effect Of Platform Connection And Abutment Material On Stress Distribution In Single Anterior Implant-supported Restorations: A Nonlinear 3-dimensional Finite Element Analysis.

Although various abutment connections and materials have recently been introduced, insufficient data exist regarding the effect of stress distribution on their mechanical performance. The purpose of this study was to investigate the effect of different abutment materials and platform connections on stress distribution in single anterior implant-supported restorations with the finite element method. Nine experimental groups were modeled from the combination of 3 platform connections (external hexagon, internal hexagon, and Morse tapered) and 3 abutment materials (titanium, zirconia, and hybrid) as follows: external hexagon-titanium, external hexagon-zirconia, external hexagon-hybrid, internal hexagon-titanium, internal hexagon-zirconia, internal hexagon-hybrid, Morse tapered-titanium, Morse tapered-zirconia, and Morse tapered-hybrid. Finite element models consisted of a 4×13-mm implant, anatomic abutment, and lithium disilicate central incisor crown cemented over the abutment. The 49 N occlusal loading was applied in 6 steps to simulate the incisal guidance. Equivalent von Mises stress (σvM) was used for both the qualitative and quantitative evaluation of the implant and abutment in all the groups and the maximum (σmax) and minimum (σmin) principal stresses for the numerical comparison of the zirconia parts. The highest abutment σvM occurred in the Morse-tapered groups and the lowest in the external hexagon-hybrid, internal hexagon-titanium, and internal hexagon-hybrid groups. The σmax and σmin values were lower in the hybrid groups than in the zirconia groups. The stress distribution concentrated in the abutment-implant interface in all the groups, regardless of the platform connection or abutment material. The platform connection influenced the stress on abutments more than the abutment material. The stress values for implants were similar among different platform connections, but greater stress concentrations were observed in internal connections.

Diet Carotenoid Lutein Modulates The Expression Of Genes Related To Oxygen Transporters And Decreases Dna Damage And Oxidative Stress In Mice.

Lutein (LT) is a carotenoid obtained by diet and despite its antioxidant activity had been biochemically reported, few studies are available concerning its influence on the expression of antioxidant genes. The expression of 84 genes implicated in antioxidant defense was quantified using quantitative reverse transcription polymerase chain reaction array. DNA damage was measured by comet assay and glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) were quantified as biochemical parameters of oxidative stress in mouse kidney and liver. cDDP treatment reduced concentration of GSH and increased TBARS, parameters that were ameliorated in treatment associated with LT. cDDP altered the expression of 32 genes, increasing the expression of GPx2, APC, Nqo1 and CCs. LT changed the expression of 37 genes with an induction of 13 mainly oxygen transporters. In treatments associating cDDP and LT, 30 genes had their expression changed with a increase of the same genes of the cDDP treatment alone. These results suggest that LT might act scavenging reactive species and also inducing the expression of genes related to a better antioxidant response, highlighting the improvement of oxygen transport. This improved redox state of the cell through LT treatment could be related to the antigenotoxic and antioxidant effects observed.