Role of conductivity in the electrohydrodynamic patterning of air-liquid interfaces

The effect of electrical conductivity on the wavelength of an electrohydrodynamic instability of a leaky dielectric-perfect dielectric (LD-PD) fluid interface is investigated. For instabilities induced by dc fields, two models, namely the PD-PD model, which is independent of the conductivity, and the LD-PD model, which shows very weak dependence on the conductivity of the LD fluid, have been previously suggested. In the past, experiments have been compared with either of these two models. In the present work, experiments, analytical theory, and simulations are used to elucidate the dependence of the wavelength obtained under dc fields on the ratio of the instability time (tau(s) = 1/s(max)) and the charge relaxation time (tau(c) = epsilon epsilon(0)/sigma, where epsilon(0) is the permittivity of vacuum, epsilon is the dielectric constant, and sigma is the electrical conductivity). Sensitive dependence of the wavelength on the nondimensional conductivity S-2 = sigma(2)mu(2)h(0)(2)/(epsilon(2)(0)f(0)(2)delta(2)) (where sigma(2) is the electrical conductivity, mu(2) is the viscosity, h(0) is the thickness of the thin liquid film, phi(0) is the rms value of the applied field, and delta is a small parameter) is observed and the PD-PD and the LD-PD cases are observed only as limiting behaviors at very low and very high values of S-2, respectively. Under an alternating field, the frequency of the applied voltage can be altered to realize several regimes of relative magnitudes of the three time scales inherent to the system, namely tau(c), tau(s), and the time period of the applied field, tau(f). The wavelength in the various regimes that result from a systematic variation of these three time scales is studied. It is observed that the linear Floquet theory is invalid in most of these regimes and nonlinear analysis is used to complement it. Systematic dependence of the wavelength of the instability on the frequency of the applied field is presented and it is demonstrated that nonlinear simulations are necessary to explain the experimental results

Electrokinetic model for electric-field-induced interfacial instabilities

Technology based on electric-field-induced instabilities on thin polymer film surfaces has emerged as a promising candidate for soft lithography. Typically, the instability is modeled using the perfect dielectric (PD) or the leaky dielectric (LD) model. These assume the electric diffuse layer to be infinitesimally large or small, respectively. In the present work we conduct stability analysis assuming a PD-electrolyte solution interface. The concentration of ions and, hence, the diffuse layer thickness is in general assumed to be of the same order as the electrolyte film thickness. The PD-LD models are then realized as limiting cases of the ratio of the double layer thickness to the film thickness

Electrohydrodynamic instabilities at interfaces subjected to alternating electric field

Instabilities at the interface of two immiscible fluids, either perfect or leaky dielectrics, subjected to alternating electric fields, is studied using a linear stability analysis in the limit of the electrode spacing being large compared to the wavelength of the perturbation. The Floquet analysis of the stability of this system indicates a significant effect of the frequency on the value of s(max), the growth rate of the fastest growing instabilities and E(Taylor), the minimum field required to excite an instability. It is seen that alternating fields act to damp the system instabilities compared to the direct current (dc) case. Moreover, the growth rate of the instabilities can be tuned from that of leaky dielectric fluids subjected to dc fields, in the low frequency limit, to that of perfect dielectrics in the high frequency limit. It is also observed that for a leaky dielectric-leaky dielectric interface, the alternating current (ac) fields can induce instabilities in a system which is stable at zero frequency, by increasing the frequency of the applied voltage. (C) 2010 [doi:10.1063/1.3431043

Linear stability analysis of electrohydrodynamic instabilities at fluid interfaces in the “small feature” limit

The endeavour to effectively harness interfacial electrohydrodynamic instabilities, to create small patterns, involves reducing the wavelength of the instability. This can be accomplished by decreasing the separation between the electrodes which may not always be possible. One may therefore have to reduce the surface tension or increase the applied voltage at a fixed electrode spacing. This can result in the wavelength of the pattern becoming of the same order as the electrode separation. Pease and Russel (J. Chem. Phys. 118, 3790 (2003)) were the first to argue that the commonly used Thin-Film Approximation (TFA) that involves an asymptotic expansion in the small parameter δ = (ε 0 φ 0 2 /(γh 0))1/2 (where ε 0 is the permittivity of vacuum, φ 0 is the root mean square value of the applied potential, γ is the surface tension and h 0 is the thickness of the thin film) need not always be valid and γ may not be small in experiments. Higher-order corrections to the TFA might therefore be necessary. We extend the Direct Current (DC) field analysis of Pease and Russel to an Alternating Current (AC) field. AC field has been suggested as an effective way of controlling the wavelength of electrohydrodynamic instabilities at fluid-fluid interfaces. Infact, the perfect and leaky dielectric limits can be realised in the same fluid at very high and very low electric field frequencies, respectively. Recently, Roberts and Kumar (J. Fluid Mech. 631, 255 (2009)) carried out an analysis using TFA to investigate AC-field-induced instabilities at air-polymer interfaces. We propose a Generalized Model (GM), without the lubrication approximation, and carry out detailed comparison with the TFA. We consider the top fluid to be air, a perfect dielectric, and the bottom fluid to be a perfect or a leaky dielectric. The analysis is carried out for both DC and AC fields, and the deviation from TFA is expressed in terms of the parameter B = γh 0/(ε 0 φ 0 2 ) = δ − 2. We discuss variation of the wavelength of the fastest growing mode with frequency of the applied field for any arbitrary value of B, unlike the analysis of Roberts and Kumar which is restricted to B ≫ 1(δ ≪ 1) . We also revisit the analysis of Pease and Russel for instabilities under DC field and present the results in terms of the single parameter, B

New Trend in Infinitely Variable Transmission System Based On Cam

ABSTRACT: A Cam-based Infinitely Variable Transmission is a type of transmission that allows an infinitely variable ratio change within a finite range, allowing the engine to continuously operate in an efficient or high performance range. A Cam-based Infinitely Variable Transmission system is a drive mechanism with one set of planetary gears & a cam with three followers mounted on carrier. The followers can be shifted in relation to the three dimensional cam by shifter mechanism due to which followers oscillation magnitude changes. The one way clutch use to transfer positive motion of follower to planet gear. The mechanism adapted for infinitely variable output between range 0 to1/4 th of input speed. It maintains a uniform output for a given uniform input

Alcohol Detection And Monitering System For Vehicles

In this project we have used an alcohol detecting sensor in vehicle for safe driving system of vehicle for drunk and driving cases, which senses and detects alcohol particles and send messages if alcohol concentration is above hazardous level. In this process GSM and GPS modules are connected to microcontroller for controlling purpose.GPS module get the position of vehicle with longitude and latitude and it send message to authorized person. We have also provided the security system for vehicle that is keypad for giving password to secure the vehicle

Statistical optimization of dithranol-loaded solid lipid nanoparticles using factorial design

This study describes a 3² full factorial experimental design to optimize the formulation of dithranol (DTH) loaded solid lipid nanoparticles (SLN) by the pre-emulsion ultrasonication method. The variables drug: lipid ratio and sonication time were studied at three levels and arranged in a 3² factorial design to study the influence on the response variables particle size and % entrapment efficiency (%EE). From the statistical analysis of data polynomial equations were generated. The particle size and %EE for the 9 batches (R1 to R9) showed a wide variation of 219-348 nm and 51.33- 71.80 %, respectively. The physical characteristics of DTH-loaded SLN were evaluated using a particle size analyzer, differential scanning calorimetry and X-ray diffraction. The results of the optimized formulation showed an average particle size of 219 nm and entrapment efficiency of 69.88 %. Ex-vivo drug penetration using rat skin showed about a 2-fold increase in localization of DTH in skin as compared to the marketed preparation of DTH.<br>Este estudo descreve o planejamento factorial 3² para otimizar a formulação de nanopartículas lipídicas sólidas (SLN) carregadas com ditranol (DTH) pelo método da ultrassonificação pré-emulsão. As variáveis como proporção de fármaco:lipídio e o tempo de sonicação foram estudados em três níveis e arranjados em planejamento fatorial 3² para estudar a influência nas variáveis de resposta tamanho de partícula e eficiência percentual de retenção do fármaco (%EE). Pela análise estatística, geraram-se equações polinomiais. O tamanho da partícula e a %EE para os 9 lotes (R1 a R9) mostraram ampla variação, respectivamente, 219-348 nm e 51,33-71,80%. As características físicas das SLN carregadas com DTN foram avaliadas utilizando-se analisador de tamanho de partícula, calorimetria de varredura diferencial e difração de raios X. Os resultados da formulação otimizada mostraram tamanho médio de partícula de 219 nm e eficiência de retenção do fármaco de 69,88%. A penetração ex vivo do fármaco utilizando pele de rato mostrou aumento de, aproximadamente, duas vezes na localização de DTH na pele, comparativamente à preparação de DTH comercializada