153 research outputs found
Coalescence in low-viscosity liquids
The expected universal dynamics associated with the initial stage of droplet
coalescence are difficult to study visually due to the rapid motion of the
liquid and the awkward viewing geometry. Here we employ an electrical method to
study the coalescence of two inviscid droplets at early times. We measure the
growth dynamics of the bridge connecting the two droplets and observe a new
asymptotic regime inconsistent with previous theoretical predictions. The
measurements are consistent with a model in which the two liquids coalesce with
a slightly deformed interface.Comment: 4 pages and 4 figure
Thermodynamic behaviour and structural properties of an aqueous sodium chloride solution upon supercooling
We present the results of a molecular dynamics simulation study of
thermodynamic and structural properties upon supercooling of a low
concentration sodium chloride solution in TIP4P water and the comparison with
the corresponding bulk quantities. We study the isotherms and the isochores for
both the aqueous solution and bulk water. The comparison of the phase diagrams
shows that thermodynamic properties of the solution are not merely shifted with
respect to the bulk. Moreover, from the analysis of the thermodynamic curves,
both the spinodal line and the temperatures of maximum density curve can be
calculated. The spinodal line appears not to be influenced by the presence of
ions at the chosen concentration, while the temperatures of maximum density
curve displays both a mild shift in temperature and a shape modification with
respect to bulk. Signatures of the presence of a liquid-liquid critical point
are found in the aqueous solution. By analysing the water-ion radial
distribution functions of the aqueous solution we observe that upon changing
density, structural modifications appear close to the spinodal. For low
temperatures additional modifications appear also for densities close to that
corresponding to a low density configurational energy minimum.Comment: 10 pages, 13 figures, 2 tables. To be published in J. Chem. Phy
The Hydrogen Evolution and Oxidation Kinetics during Overdischarging of Sealed Nickel-Metal Hydride Batteries
Porous silicon formation and electropolishing
Electrochemical etching of silicon in hydrofluoride containing electrolytes
leads to pore formation for low and to electropolishing for high applied
current. The transition between pore formation and polishing is accompanied by
a change of the valence of the electrochemical dissolution reaction. The local
etching rate at the interface between the semiconductor and the electrolyte is
determined by the local current density. We model the transport of reactants
and reaction products and thus the current density in both, the semiconductor
and the electrolyte. Basic features of the chemical reaction at the interface
are summarized in law of mass action type boundary conditions for the transport
equations at the interface. We investigate the linear stability of a planar and
flat interface. Upon increasing the current density the stability flips either
through a change of the valence of the dissolution reaction or by a nonlinear
boundary conditions at the interface.Comment: 18 pages, 8 figure
Reaction-Diffusion Processes with Nonlinear Diffusion
We study reaction-diffusion processes with concentration-dependent
diffusivity. First, we determine the decay of the concentration in the
single-species and two-species diffusion-controlled annihilation processes. We
then consider two natural inhomogeneous realizations. The two-species
annihilation process is investigated in the situation when the reactants are
initially separated, namely each species occupies a half space. In particular,
we determine the growth law of the width of the reaction zone. The
single-species annihilation process is studied in the situation when the
spatially localized source drives the system toward the non-equilibrium steady
state. Finally we investigate a dissolution process with a localized source of
diffusing atoms which react with initially present immobile atoms forming
immobile molecules.Comment: Figure and references added, final versio
Interfacial electron transfer as a significant step in photoelectrochemical reactions on some semiconductors
Photoelectrochemical kinetics at the semiconductor-solution interface has been considered in all treatments in the literature, except one, to be rate controlled by processes inside the semiconductor. Evidence is presented which suggest that, at least for cathodic reactions on p-CdTe, the rate determining step is interfacial electron transfer, and a part of the total potential difference at the interface exists in the Helmholtz layer. Journal of Applied Physics is copyrighted by The American Institute of Physics
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