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The study explores the stable levitation and self-organization of charged multi-drop assemblies in a large sized quadrupole trap both experimentally and through numerical simulations. The trap is benchmarked by comparing single drop levitation experiments with numerical simulations. Important observation and findings of the study are: (i) long time stabilization and formation of patterns of droplet collections over a range of operating parameters (ii) Numerical prediction of polygonal patterns for few drop (2 to 8) systems and lattice structures for many drop (>10) systems, (iii) Numerical prediction of Non-dependence of the inter-drop spacing on droplet charge for similarly charged drops, consistent with earlier analytical formulations [Aardahl et al., J. Aerosol Sci. 28, 1491-1505 (1997)], (iv) numerical observation of two drops oscillations with a secular frequency distinctly higher than the single drop Dehmelt frequency (v) Simulations of a systematic transition from disordered to coulombic crystals with mean size increasing with the number of levitated drops (N) as similar to N-0.29. The experimental observations on different patterns and lattice spacings are closely reproduced by simulations. Published by AIP Publishing.

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]

Rayleigh instability of charged conducting drops, in the viscous regime, is analyzed in the presence of counterions in the surrounding fluid. The Rayleigh criterion for the instability is derived in the Debye-Huckel approximation. It is found that the critical charge for the instability is reduced in the presence of counterions. The analysis is carried out for charged vesicles, with symmetric double layers across the bilayer, and the critical charge for the instability is determined. It is found that vesicles can indeed become unstable at high surface potentials. These results should be important in biological systems, where cells, with charged membranes, are immersed in electrolyte solutions. Additionally, the expression for the decay rate for vesicles with charged bilayers should give better estimates for the correlation time of the shape fluctuations. (C) 2010 [doi: 10.1063/1.3361158]