Showing papers by "Anand Yethiraj published in 2016"
TL;DR: It is demonstrated that the pulsed-field gradient NMR technique, with its spectral separation of different chemical components, is ideal for studying the dynamics of the entire system simultaneously and without labelling, in a wide range of systems.
26 citations
TL;DR: This work reports a novel form of multi-scale flow, driven by an external electric field, in a highly viscous oil-in-oil emulsion system consisting of micron-size droplets, which leads to dynamical organization at spatial scales much larger than that of the individual droplets.
Abstract: Efficient mixing strategies in a fluid involve generation of multi-scale flows which are strongly suppressed in highly viscous systems. In this work, we report a novel form of multi-scale flow, driven by an external electric field, in a highly viscous (η ∼ 1 Pa s) oil-in-oil emulsion system consisting of micron-size droplets. This electro-hydrodynamic flow leads to dynamical organization at spatial scales much larger than that of the individual droplets. We characterize the dynamics associated with these structures by measuring the time variation of the bulk Reynolds stress in a rheometer, as well as through a micro-scale rheometric measurement by probing the spectrum of fluctuations of a thin fiber cantilever driven by these flows. The results display scale invariance in the energy spectra over three decades with a power law reminiscent of turbulent convection. We also demonstrate the mixing efficiency in such micro-scale systems.
12 citations
TL;DR: This work finds that the electric capillary number, CaE, at the threshold of drop breakup is of order unity for cell thicknesses of 100 μm or thicker, but much larger for thinner cells, and there is a clear transition to super-diffusive droplet motions above this threshold.
Abstract: A two-fluid emulsion (silicone oil drops in the “leaky dielectric”, castor oil) with electrohydrodynamically driven flows can serve as a model system for tunable studies of hydrodynamic interactions [Varshney et al., Sci. Rep., 2012, 2, 738]. Flows on multiple length- and time-scales have been observed but the underlying mechanism for these chaotic, multi-scale flows is not understood. In this work, we conducted experiments varying the thickness of the test cell to examine the role of substrate interactions on size distribution, mean square displacement and velocity of the drops as a function of the electric field strength. We find that the electric capillary number, CaE, at the threshold of drop breakup is of order unity for cell thicknesses of 100 μm or thicker, but much larger for thinner cells. Above this threshold, there is a clear transition to super-diffusive droplet motions. In addition, we observe that there is a convective instability prior to the onset of chaotic flows, with the lengthscale associated with the convection rolls increasing linearly with an increase in the cell thickness. The fact that the convective instability appears to occur in the leaky dielectric castor oil regardless of whether the second component is liquid drops, solid particles, or dissolved dye has implications on the underlying mechanism for the unsteady flows.
11 citations
TL;DR: This is the equation used for all local bond order parameter calculations discussed in the manuscript, and therefore all of the results and conclusions are unaffected by this error.
Abstract: where Ψs is the length-weighted local bond order parameter (where s can be 4 or 6), N is the number of the nearest neighbors of each lattice point, lj is the length of the side between the jth and (j+1)th neighbor of the polygon formed by the nearest neighbors around each lattice point, and θj is the angle between a reference axis and the line connecting that lattice point to its jth nearest neighbor. This is the equation we used for all local bond order parameter calculations discussed in the manuscript, and therefore all of our results and conclusions are unaffected by this error. We note that this length-weighting scheme was used by one of us in an earlier publication. Furthermore, we thank Wenceslao Gonzaĺez-Vinas (University of Navarra, Spain) for pointing out that this quantity is identical to the Minkowski structure metric.
1 citations