323 research outputs found
Electric double layer structure close to the three-phase contact line in an electrolyte wetting a solid substrate
The electric double layer structure in an electrolyte close to a solid
substrate near the three-phase contact line is approximated by considering the
linearized Poisson-Boltzmann equation in a wedge geometry. The mathematical
approach complements the semi-analytical solutions reported in the literature
by providing easily available characteristic information on the double layer
structure. In particular, the model contains a length scale that quantifies the
distance from the fluid-fluid interface over which this boundary influences the
electric double layer. The analysis is based on an approximation for the
equipotential lines. Excellent agreement between the model predictions and
numerical results is achieved for a significant range of contact angles. The
length scale quantifying the influence of the fluid-fluid interface is
proportional to the Debye length and depends on the wall contact angle. It is
shown that for contact angles approaching 90{\deg} there is a finite range of
boundary influence.Comment: 6 pages, 9 figures;
http://link.aps.org/doi/10.1103/PhysRevE.86.02260
Influence of the enclosed fluid on the flow over a microstructured surface in the Cassie state
Analytical expressions for the flow field as well as for the effective slip
length of a shear flow over a surface with periodic rectangular grooves are
derived. The primary fluid is in the Cassie state with the grooves being filled
with a secondary immiscible fluid. The coupling of both fluids is reflected in
a locally varying slip distribution along the fluid-fluid interface, which
models the effect of the secondary fluid on the outer flow. The obtained
closed-form analytical expressions for the flow field and effective slip length
of the primary fluid explicitly contain the influence of the viscosities of the
two fluids as well as the magnitude of the local slip, which is a function of
the surface geometry. They agree well with results from numerical computations
of the full geometry. The analytical expressions allow investigating the
influence of the viscous stresses inside the secondary fluid for arbitrary
geometries of the rectangular grooves. For classic superhydrophobic surfaces,
the deviations in the effective slip length compared to the case of inviscid
gas flow are are pointed out. Another important finding with respect to an
accurate modeling of flow over microstructured surfaces is that the local slip
length of a grooved surface is anisotropic.Comment: submitted to the Journal of Fluid Mechanic
Coupled self-organization: Thermal interaction between two liquid films undergoing long-wavelength instabilities
The effects of thermal coupling between two thin liquid layers, separated by
a gas layer, are discussed. The liquid layers undergo long-wavelength
instabilities driven by gravitational and thermocapillary stresses. To study
the dynamics, both a linear stability analysis and a full numerical solution of
the thin-film equations are performed. The results demonstrate that the
stability properties of the combined system differ substantially from the case
where both layers evolve independently from each other. Most prominently,
oscillatory instabilities, not present in single-liquid layer configurations,
may occur.Comment: 12 pages, 9 figure
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