Shape of the Capillary Meniscus around an Electrically Charged Particle at a Fluid Interface:  Comparison of Theory and Experiment

Abstract

Here, we consider in detail the problem of the shape of the capillary meniscus around a charged colloidal particle, which is attached to a fluid interface: oil/water or air/water. The meniscus profile is influenced by the electric field created by charges at the particle/nonpolar fluid boundary. We digitized the coordinates of points from the meniscus around silanized glass spheres (200-300 mum in radius) attached to the tetradecane/water interface. The theoretical meniscus shape is computed in three different ways that give numerically coincident results. It is proven that for sufficiently small particles the meniscus profile can be expressed as a superposition of pure electric and gravitational deformations. Special attention is paid to the comparison of theory and experiment. A procedure for data processing is developed that allows one to obtain accurate values of the contact angle and surface charge density from the fit of the experimental meniscus profile. For all investigated particles, excellent agreement between theory and experiment is achieved. The results indicate that the electric field gives rise to an interfacial deformation of medium range and considerable amplitude.

Interaction between like-charged particles at a liquid interface: Electrostatic repulsion vs. electrocapillary attraction

“…by charges, located at the particle/nonpolar-fluid interface, practically does not penetrate into the water phase; see, for example, the known problems for the image-charge effect [45,48] and for a hydrophobic particle near an oil-water interface [49]. Experimentally, the non-penetration of the field into water is manifested as independence of the configuration of the adsorbed particles on the electrolyte concentration in the aqueous phase [25,27,41]. Moreover, charges on the particle/water interface can also create a long-range electric field that penetrates in the nonpolar fluid trough the particle [36][37][38], whereas their electric field is suppressed in the aqueous phase by the Debye screening.…”

“…The existence of electrodipping force, F ED , that pushes a charged particle toward the phase of greater dielectric constant was experimentally proven with particles at air/water and oil/water interfaces, and theory for the calculation of this force was developed [25,26]. The meniscus shape around individual charged particles was experimentally determined and the results were compared with the theoretical predictions [27].…”

“…(1.1) accounts for the fact that the dipolar field occupies only the upper half-space (the nonpolar fluid), whereas the electric field in the aqueous phase is screened by the ions in water. The electric charges that create the electric field can be located at the particle/water interface [22,29,[36][37][38] and/or on the particle/nonpolar-fluid interface [9,10,[25][26][27]34,35,[39][40][41][42][43]. Eq.…”

In situ lipid dip‐pen nanolithography under water

“…Upon contact with the surface, an oil-in-water meniscus forms, allowing the lipid ink to be transported to the surface. Although the term meniscus is most commonly used to refer to a curved liquid/vapor interface in contact with a solid surface, the same interface-physics concepts apply when any two immiscible fluids are used (BrochardWyart 1995), for example oil and water (Danov et al 2006). Using the same tip for deposition and imaging in solution (where capillary condensation no longer disrupts the pattern during imaging) permits quantification of the spreading kinetics of lipid bilayers.…”

Effective interactions of colloids on nematic films

“…[15]) and also parallels the tentative explanation given for the experimentally observed attractions between sub-μm charged colloids at a water-oil interface [16] (for the controversy around this explanation see, Refs. [17][18][19][20][21][22][23][24]). …”