Influence of nano-SiO2 on dilational viscoelasticity of liquid/air interface of cetyltrimethyl ammonium bromide

An investigation was reported on the interfacial rheology of nano-SiO₂ dispersions in the presence of cetyltrimethyl ammonium bromide (CTAB). The interfacial dilational viscoelasticity had been measured as a function of the nano-particle concentration. The properties of the interface were affected by different processes such as the surfactants adsorption at the liquid or at the particle interfaces. It was found that the influence of nano-SiO₂ particles on the interfacial properties was evident and complex. The property of SiO₂ particles would change from hydrophilic to hydrophobic when CTAB molecules absorbed at their surface. The reorganization of surfactants and the participation of hydrophobic SiO₂ at the surface were offered to explain the process. In particular, the interaction between surfactants and particles, and the transfer of particles from bulk to the surface played an important role in changing the properties of the interface.     

Effect of substrate bias voltage on corrosion of TiN/Ti multilayers deposited by magnetron sputtering

Austenitic stainless steel can be attack by localized corrosion in saline environments, such as seawater. TiN/Ti multilayers can improve the corrosion resistance of the stainless steel better than TiN monolayers, because the titanium layers improve the impermeability of TiN/Ti multilayers. In this work, 1.75-4.55 μm thick layers were deposited on to grounded or −100 V biased substrates of 304 stainless steel substrates by reactive magnetron sputtering. The corrosion resistance of the layers was studied by means of potentiodynamic polarization in 0.5 M NaCl solutions. It was found that the pitting corrosion resistance was dependent on the bias and period number of the multilayers.     

Mechanics of plasma exposed spin-on-glass (SOG) and polydimethyl siloxane (PDMS) surfaces and their impact on bond strength

Silicone polymer (PDMS), widely used for micro-fluidic and biosensor applications, possesses an extremely dynamic surface after it is subjected to an oxygen plasma treatment process. The surface becomes extremely hydrophilic immediately after oxygen plasma exposure by developing silanol bond (SiOH), which promotes its adhesion to some other surfaces like, silicon, silicon dioxide, glass, etc. Such a surface, if left in ambient dry air, shows a gradual recovery of hydrophobicity. We have found an identical behavior to occur to surfaces coated with a thin continuous film of SOG (methyl silsesquioxane). The chemistry induced by oxygen plasma treatment of a spin-on-glass (SOG) coated surface provides a much higher density of surface silanol groups in comparison to precleaned glass, silicon or silicon dioxide substrates thus providing a higher bond strength with polydimethyl siloxane (PDMS). The bonding protocol developed by using the spin coated and cured SOG intermediate layer provides an universal regime of multi level wafer bonding of PDMS to a variety of substrates. The paper describes a contact angle based estimation of bond strength for SOG and PDMS surfaces exposed to various combinations of plasma parameters. We have found that the highest bond strength condition is achieved if the contact angle on the SOG surface is less than 10°.     

Formation and mobility of droplets on composite layered substrates

A mesoscale fluid film placed on a solid support may break up and form droplets. In addition, droplets may exhibit spontaneous translation by modifying the wetting properties of the substrate, resulting in asymmetry in the contact angles. We examine mechanisms for droplet formation and motion on uniform and terraced landscapes, i.e., composite substrates. The fluid film stability, droplet formation and velocity are studied theoretically in the isothermal case using a lubrication approach in one spatial dimension. The droplet properties are found to involve contributions from both the terraced layer thickness and molecular interactions via the disjoining potential.     

Photoacoustic cavitation and heat transfer effects in the laser-induced temperature jump in water

The finite element method is employed to analyze photoacoustic cavitation and heat transfer occurring when modest temperature jumps (T-jumps) are induced by a laser in D₂O solution, which may contain a small concentration of a protein or peptide sample. Cavitation can be initiated through a photoacoustic mechanism at intensities well below optical breakdown thresholds. Cavitation probability is related to test medium properties, initial temperature, T-jump magnitude and test region geometry. Parameters affecting thermal conduction losses are also examined because such losses limit the useful duration of the T-jump induced in protein folding experiments. From this study, guidelines are offered for reducing the occurrence of cavitation and extending the useful duration of the T-jump. Received: 2 April 2001 / Revised version: 17 October 2001 / Published online: 29 November 2001     

Dependence of thermoluminescence response of calcium sulphate activated by dysprosium on the temperature irradiation

Radiation dosimetry is a very important issue in space research and in experiments that try to simulate chemical processes that may occur in cometary nucleus, interstellar grains, and other extraterrestrial environments, due to their irradiation by cosmic rays. The temperature effect is an important factor that has not been considered in many of these experiments. In this work, this effect was studied in TLD dosimeters exposed to gamma rays. The irradiations were done from 77 to 298 K in a Gamma cell unit with a dose rate of 1.0 Gy/s. Results obtained for CaSO₄:Dy show that there is a considerable effect in the evaluation of the dose as function of the irradiation temperature.     

The collapse and rebound of gas-vapor cavity on metal surface

The oscillation property of a gas-vapor cavity near a solid boundary is investigated by a sensitive fiber-optic sensor based on optical beam deflection principle when a high-intensity laser pulse is focused on an aluminum surface in water. The temporal and spatial evolutions of the bubble wall during the expansion and collapse are traced according to sequence waveforms induced by the bubble motion. Both the maximum and minimum bubble radii at each oscillating cycle are determined by experiment. Further, in combination with the spherical bubble theory, the variation of the gas content remaining in the cavity during each pulsation is estimated by the method of fitting curve. The results show that about half of the gas content is dissolved into the surrounding water during the whole process. The less gas content in the cavity makes the bubble contract more violently. The corresponding minimum radius and the collapsing duration become smaller and shorter.     

Dependence of the ordinary hall constant on the temperature and alloying-element concentration

An equation is derived for the Hall constant for the case of a binary disordered solid solution on the basis of two-band theory. The equation explains the change in the sign of the Hall emf at certain alloying-element concentrations. An equation is found for the temperature coefficient of the Hall constant for a compensated metal; this equation explains the decrease in this coefficient with increasing temperature and the change in sign at certain alloying-element concentrations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 59–64, March, 1971.     

Oscillation characteristics of a laser-induced cavitation bubble in water at different temperatures

Comprehensive numerical and experimental analyses of the effect of temperature on cavitation oscillations are performed. In the experimental study, the oscillation of a laser-generated single cavitation bubble near a rigid boundary is obtained using a fiber-optic diagnostic technique based on optical beam detection (OBD). The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. And cavitation bubble tests are performed using water at different temperatures, and its temperature ranges from freezing point (0 °C) to near boiling. Furthermore, a modified Rayleigh-Plesset equation is derived for calculating the temporal development of the bubble radius at different temperatures. Both the experimental and the numerical results show that the maximum bubble radius and bubble lifetime both increase as temperature increases. The mechanism behind it has also been discussed.     

Dependence of Curie temperature on surface strain in InMnAs epitaxial structures

Pairs of self-assembled InMnAs quantum dot structures and reference epitaxial layers (0 < x < 0.13) were prepared on GaAs substrates by low-pressure metal organic vapour phase epitaxy. Magnetic moment measurements indicated that reference epitaxial layer had a Curie temperature of 343 K independent on the composition. On the other hand, the quantum dots prepared under Stranski-Krastanov growth mode from the identical gas phase composition showed a lower value of Curie temperature. This value varied from 41 to 235 K in relation to the material composition. Moiré fringes at transmission electron microscopy plan view were used for characterization of strain in InMnAs quantum dot structures.     

Relaxation on the energy method for the transient Rayleigh-Bénard convection

The onset of buoyancy-driven instability in initially quiescent fluid layers having the various boundary conditions is analyzed by using the energy method. New energy stability equation is derived under the Boussinesq approximation and the relative stability concept. The predicted critical conditions are compared with the previous results based on the conventional energy method. The stability limits which are related to the onset time of instabilities are presented as a function of the Rayleigh number Ra and the Prandtl number Pr. The present stability results predict that the onset time of convective instability decreases with increasing Ra and Pr. For the case of high Ra, the onset time of the instability is relatively insensitive to the boundary conditions of the upper boundaries.     

Age-induced oxide on cleaved surface of layered GaSe single crystals

It is shown that a long-term keeping of a layered gallium monoselenide at room temperature results in formation of the intrinsic oxide at a cleaved surface of semiconductor. It is found that the chemical compositions of the intrinsic oxide at the surfaces of the intentionally undoped and doped samples of GaSe are different. The electrical properties of the GaSe-intrinsic oxide system are presented. It is established that intrinsic oxide films at the surface of GaSe are characterized by current instability with N-type current-voltage characteristic. The influence of relative humidity on changes of capacitance and surface resistivity of the intrinsic oxide is also discussed.     

Dependence of helium ion diffusion and drift characteristics in own gas on its temperature

The low-temperature gas discharge has a number of features which can appear in experimentswith dusty plasma. For example, at cryogenic temperatures of gas-discharge tube walls, the strong anisotropy of the velocity distribution function of ions takes place, which in turn can cause a significant change in dust structure properties. The dependences of the helium ion drift characteristics in a dc uniform electric field on the atomic temperature of own gas is analyzed.     

Effect of single ion anisotropy on the critical temperature of classical quasi-one-dimensional magnets

The effect of single ion anisotropy energy on the three-dimensional ordering temperature of a classical quasi-one-dimensional magnetic chain is estimated using a mean field approximation for the interchain coupling and a classical spin field model for a chain. Numerical results are presented for T_c as a function of the interchain and interchain exchange interactions and the single ion anisotropy.     

Instability and dynamics of thin viscoelastic liquid films

The instability, rupture, and subsequent growth of holes in a thin Jeffreys-type viscoelastic film under the influence of long-range van der Waals force are investigated using both linear stability analysis and nonlinear numerical solutions. The linear stability analysis of full governing equations valid for arbitrary wave numbers shows that although fluid rheology does not influence the dominant length scale of the instability, it significantly affects the growth rate. It is shown that neglect of inertia and solvent dynamics results in a nonphysical singularity in the growth rate beyond a critical value of relaxation time. We further carry out numerical simulations of a set of long-wave, nonlinear differential equations (also derived in Rauscher et al., Eur. Phys. J. E 17, 373 (2005)) governing the evolution of the free surface. The nonlinear simulations, in their domain of validity, confirm the results of the linear analysis. Interestingly, results from nonlinear simulations further show that both for Newtonian and viscoelastic liquids, the shape and the dewetting dynamics of a hole are identical when examined in terms of a rescaled time which depends on rheological parameters. Thus, viscoelasticity of Jeffreys type merely accelerates the growth rate, without however affecting the important morphological characteristics.     

Single fiber model of particle retention in an acoustically driven porous mesh

A method for the capture of small particles (tens of microns in diameter) from a continuously flowing suspension has recently been reported. This technique relies on a standing acoustic wave resonating in a rectangular chamber filled with a high-porosity mesh. Particles are retained in this chamber via a complex interaction between the acoustic field and the porous mesh. Although the mesh has a pore size two orders of magnitude larger than the particle diameter, collection efficiencies of 90% have been measured. A mathematical model has been developed to understand the experimentally observed phenomena and to be able to predict filtration performance. By examining a small region (a single fiber) of the porous mesh, the model has duplicated several experimental events such as the focusing of particles near an element of the mesh and the levitation of particles within pores. The single-fiber analysis forms the basis of modeling the overall performance of the particle filtration system.     

Destruction of the family of steady states in the planar problem of Darcy convection

We consider natural convection of an incompressible fluid in a porous medium described by the planar Darcy equation. For some boundary conditions, Darcy problem may have non-unique solutions in form of a continuous family of steady states. We are interested in the situation when these boundary conditions are violated. The resulting destruction of the family of steady states is studied via computer experiments based on a mimetic finite-difference approach. Convection in a rectangular enclosure is considered under different perturbations of boundary conditions (heat sources, infiltration). Two scenario of the family of equilibria are found: the transformation to a limit cycle and the formation of isolated convective patterns.     

Dependence of the temperature behaviour of the sputtering ratio on the channelled fraction of the ion beam

A method of calculation is presented for the yield of an electron excitation process by a channelled particle in a single encounter with an atomic row or plane in a crystal. It is shown that, if ψ is the initial angle between the ion trajectory and the row or plane, the number of inner-shell electrons excited is an increasing function of ψ whereas the number of outer electrons excited may decrease with increasing ψ.