Synthesis and characterization of silicone polymer/functionalized mesostructured silica composites

A thermally stable and flexible composite has been synthesized by following a consecutive `two-step', solvent free route. Silicone polymer containing internal hydrides was used as a polymer matrix and mesoporous silica functionalized with allytrimethoxysiloxane was used as a filler material. In the second step, the composite preparation was carried out using the hydrosilylation reaction mediated by `Karastedt' platinum catalyst. The results of the studies suggest that the composites are thermally stable, hydrophobic and flexible and can be potentially used for encapsulating flexible electronic devices.

Collision Cones for Quadric Surfaces

The problem of collision prediction in dynamic environments appears in several diverse fields, which include robotics, air vehicles, underwater vehicles, and computer animation. In this paper, collision prediction of objects that move in 3-D environments is considered. Most work on collision prediction assumes objects to be modeled as spheres. However, there are many instances of object shapes where an ellipsoidal or a hyperboloid-like bounding box would be more appropriate. In this paper, a collision cone approach is used to determine collision between objects whose shapes can be modeled by general quadric surfaces. Exact collision conditions for such quadric surfaces are obtained in the form of analytical expressions in the relative velocity space. For objects of arbitrary shapes, exact representations of planar sections of the 3-D collision cone are obtained.

Utilizing Model Nanostructured Porous Inorganic Compounds Such as Silica to Beneficially Confine “Bio”-Relevant Molecules and Demonstrate their Potential in Therapeutics

Abstract | The importance of well-defined inorganic porous nanostructured materials in the context of biotechnological applications such as drug delivery and biomolecular sensing is reviewed here in detail. Under optimized conditions, the confinement of “bio”-relevant molecules such as pharmaceutical drugs, enzymes or proteins inside such inorganic nanostructures may be remarkably beneficial leading to enhanced molecular stability, activity and performance. From the point of view of basic research, molecular confinement inside nanostructures poses several formidable and intriguing problems of statistical mechanics at the mesoscopic scale. The theoretical comprehension of such non-trivial issues will not only aid in the interpretation of observed phenomena but also help in designing better inorganic nanostructured materials for biotechnological applications.

Self Assembled Monolayers of Alkanethiolson Silver Surfaces

This short review compiles the studies on self assembled alkanethiol monolayers formed on silver surfaces with respect to their structure and stability. Alkanethiol-based assemblies on silver surfaces are poor cousins of thiol monolayers on gold. The formation of well-ordered monolayers on silver surfaces is relatively more difficult than the corresponding systems on gold since the inherent oxide film on silver interferes with the formation and stability of the assembly. There are contradictory reports on the nature and physicochemical characteristics of alkanethiol monolayers on silver surfaces. This review attempts to highlight various studies in the literature including our efforts in this area.

Planform structure of turbulent free convection on horizontal surfaces

The planform structure of turbulent free convection over a heated horizontal surface has been visualized and analyzed for different boundary conditions at the top and for different aspect ratios, for flux Rayleigh numbers ranging from 10 exp 8 - 10 exp 10. The different boundary conditions correspond to Rayleigh-Benard convection, open convection with evaporation at the top and with an imposed external flow on the heated boundary. Without the external flow the planform is one randomly oriented line plume. At large Ra, these line plumes seem to align along the diagonal, persumably due to a large-scale flow along as visualized in the side view. When the external flow is imposed, the line plumes clearly align in the direction of external flow. Flow visualization reveals that at these Ra, the shear tends to break the plumes which otherwise would reach the opposite boundary. (Author)

Numerical simulation of nano-indentation on rough surfaces

Nano-indentation is a technique used to measure various mechanical properties like hardness, Young's modulus and the adherence of thin films and surface layers. It can be used as a quality control tool for various surface modification techniques like ion-implantation, film deposition processes etc. It is important to characterise the increasing scatter in the data measured at lower penetration depths observed in the nano-indentation, for the technique to be effectively applied. Surface roughness is one of the parameters contributing for the scatter. This paper is aimed at quantifying the nature and the amount of scatter that will be introduced in the measurement due to the roughness of the surface on which the indentation is carried out. For this the surface is simulated using the Weierstrass-Mandelbrot function which gives a self-affine fractal. The contact area of this surface with a conical indenter with a spherical cap at the tip is measured numerically. The indentation process is simulated using the spherical cavity model. This eliminates the indentation size effect observed at the micron and sub-micron scales. It has been observed that there exists a definite penetration depth in relation to the surface roughness beyond which the scatter is reduced such that reliable data could be obtained.

Plumes Dynamics and Heat Transfer over Horizontal Grooved Surfaces

This study investigates the free convection and plumes dynamics over horizontal surfaces with parallel V-grooves. The convection is studied in a tank of water with the bottom surface being a smooth or grooved surface and the top of the water surface exposed to ambient. Two groove heights were used-10 mm and 3 mm-and the experiment was done with two values of aspect ratio-2.9 and 1.8 (aspect ratio is the width of the fluid layer/height of fluid layer). Heat flux at the bottom surface was from electrical heating. Beyond a certain critical temperature difference, enhanced heat transfer is obtained on the grooved surface compared to a smooth surface. Nusselt numbers are evaluated for both smooth and grooved surfaces and correlated using modified Rayleigh numbers. Visualization shows that the enhanced heat transport in the rough cavities cannot be ascribed to the increase in the contact area; rather, it must be the local dynamics of the thermal boundary layer.

Flow visualization in turbulent free convection over horizontal smooth and grooved surfaces

The present paper discusses the flow visualization for turbulent free convection in a tank of water with the bottom surface being a smooth or a grooved surface and the top of the water surface exposed to ambient. The grooved surface is of parallel 90 degrees V-grooves with groove height of 10 mm and groove width of 20 mm. The experiment is carried out with aspect ratio (AR) of 2.9 and Rayleigh number (Ra) in the range, 1.3 x 10(7) - 4 x 10(7). Here AR is the aspect ratio (= width of fluid layer/height of fluid layer). Heat flux at the bottom surface is from electrical heating. From the pH-dye visualization, interesting flow structures are observed and these structures are analyzed with the help of plumes dynamics and temperature variations with time. (C) 2011 Elsevier Ltd. All rights reserved.

Junction between surfaces of two topological insulators

We study the properties of a line junction which separates the surfaces of two three-dimensional topological insulators. The velocities of the Dirac electrons on the two surfaces may be unequal and may even have opposite signs. For a time-reversal invariant system, we show that the line junction is characterized by an arbitrary parameter alpha which determines the scattering from the junction. If the surface velocities have the same sign, we show that there can be edge states which propagate along the line junction with a velocity and spin orientation which depend on alpha and the ratio of the velocities. Next, we study what happens if the two surfaces are at an angle phi with respect to each other. We study the scattering and differential conductance through the line junction as functions of phi and alpha. We also find that there are edge states which propagate along the line junction with a velocity and spin orientation which depend on phi. Finally, if the surface velocities have opposite signs, we find that the electrons must transmit into the two-dimensional interface separating the two topological insulators.

Mixed convection adjacent to non-isothermal vertical surfaces

Study of laminar boundary layer in mixed convection from vertical plates is carried out. The surface temperature along the vertical plate is assumed to vary arbitrarily with vertical distance. Perturbation technique is used to solve the governing boundary layer equations. The differentials of the wall temperature are used as perturbation elements, which are functions of vertical distance, to obtain universal functions. The universal functions are valid for any type of vertical wall temperature variation. Heat transfer rates and fluid velocity inside the boundary layer can be expressed and calculated using these universal functions. Heat transfer rates are obtained for the special cases of power-law variation of the wall temperature. The effect of the governing parameter (Gr(y)/Re-y(2)) and the power index of the power-law wall temperature variation on heat transfer rates is studied. For the purpose of validation, the mixed convection results obtained by the present technique pertaining to the special cases of isothermal vertical wall are compared with those obtained by similarity analysis reported in literature, and the agreement is found to be good. (C) 2012 Elsevier Ltd. All rights reserved.

Substrate integrated Lead-Carbon hybrid ultracapacitor with flooded, absorbent glass mat and silica-gel electrolyte configurations

Lead-Carbon hybrid ultracapacitors (Pb-C HUCs) with flooded, absorbent-glass-mat (AGM) and silica-gel sulphuric acid electrolyte configurations are developed and performance tested. Pb-C HUCs comprise substrate-integrated PbO2 (SI-PbO2) as positive electrodes and high surface-area carbon with graphite-sheet substrate as negative electrodes. The electrode and silica-gel electrolyte materials are characterized by XRD, XPS, SEM, TEM, Rheometry, BET surface area, and FTIR spectroscopy in conjunction with electrochemistry. Electrochemical performance of SI-PbO2 and carbon electrodes is studied using cyclic voltammetry with constant-current charge and discharge techniques by assembling symmetric electrical-double-layer capacitors and hybrid Pb-C HUCs with a dynamic Pb(porous)/PbSO4 reference electrode. The specific capacitance values for 2 V Pb-C HUCs are found to be 166 F/g, 102 F/g and 152 F/g with a faradaic efficiency of 98%, 92% and 88% for flooded, AGM and gel configurations, respectively.

Directional motion of impacting drops on dual-textured surfaces

In this work, we analyze the directional movement of impacting liquid drops on dual-textured solid surfaces comprising two different surface morphologies: a textured surface and a smooth surface. The dynamics of liquid drops impacting onto the junction line between the two parts of the dual-textured surfaces is studied experimentally for varying drop impact velocity. The dual-textured surfaces used here featured a variation in their textures' geometrical parameters as well as their surface chemistry. Two types of liquid drop differing in their surface tension were used. The impact process develops a net horizontal drop velocity towards the higher-wettability surface portion and results in a bulk movement of the impacting drop liquid. The final distance moved by the impacting drop from the junction line decreases with increasing impacting drop Weber number We. A fully theoretical model, employing a balance of forces acting at the drop contact line as well as energy conservation, is formulated to determine the variation, with We, of net horizontal drop velocity and subsequent movement of the impacting drop on the dual-textured surfaces.

Meso-Structured Silica-Nafion Hybrid Membranes for Direct Methanol Fuel Cells

A series of novel organic-inorganic hybrid membranes have been prepared employing Nafion and acid-functionalized meso-structured molecular sieves (MMS) with varying structures and surface area. Acid-functionalized silica nanopowder of surface area 60 m(2)/g, silica meso-structured cellular foam (MSU-F) of surface area 470 m(2)/g and silica meso-structured hexagonal frame network (MCM-41) of surface area 900 m(2)/g have been employed as potential filler materials to form hybrid membranes with Nafion framework. The structural behavior, water uptake, proton conductivity and methanol permeability of these hybrid membranes have been investigated. DMFCs employing Nafion-silica MSU-F and Nafion-silica MCM-41 hybrid membranes deliver peak-power densities of 127 mW/cm(2) and 100 mW/cm(2), respectively; while a peak-power density of only 48 mW/cm(2) is obtained with the DMFC employing pristine recast Nafion membrane under identical operating conditions. The aforesaid characteristics of the hybrid membranes could be exclusively attributed to the presence of pendant sulfonic acid groups in the filler, which provide fairly continuous proton-conducting pathways between filler and matrix in the hybrid membranes facilitating proton transport without any trade-off between its proton conductivity and methanol crossover. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.036211jes] All rights reserved.