Sessile drop technique

About: Sessile drop technique is a research topic. Over the lifetime, 2827 publications have been published within this topic receiving 68943 citations.

On the microhydrodynamics of superspreading

Abstract: Droplets of an aqueous phase placed on a very hydrophobic, waxy surface bead-up rather than spread, forming a sessile drop with a relatively large contact angle at the edge of the drop. Surfactant molecules, when dissolved in the aqueous phase, can facilitate the wetting of an aqueous drop on a hydrophobic surface. One class of surfactants, superwetters, can cause aqueous droplets to move very rapidly over a hydrophobic surface, thereby completely wetting the surface (superspreading). A recent numerical study of the hydrodynamics of superspreading by Karapetsas, Craster & Matar (J. Fluid Mech., this issue, vol. 670, 2011, pp. 5―37) provides a clear explanation of how these surfactants cause such a dramatic change in wetting behaviour. The study shows that large spreading rates occur when the surfactant can transfer directly from the air/aqueous to the aqueous/ hydrophobic solid interface at the contact line. This transfer reduces the concentration of surfactant on the fluid interface, which would otherwise be elevated due to the advection accompanying the drop spreading. The reduced concentration creates a Marangoni force along the fluid surface in the direction of spreading, and a concave rim in the vicinity of the contact line with a large dynamic contact angle. Both of these effects act to increase the spreading rate. The molecular structure of the superwetters allows them to assemble on a hydrophobic surface, enabling the direct transfer from the fluid to the solid surface at the contact line.

Direct Visualization of the Hydrolysis Kinetics of Titanium(IV) Alkoxides on Functionalized Gold Surfaces

Abstract: The hydrolysis kinetics of titanium(IV) alkoxides coordinated on functionalized gold surfaces was monitored with video-based contact angle measurements, and the experimental data were further modeled to evaluate pseudo-first-order reaction rate constants. In particular, titanium(IV) isopropoxide molecules were attached to dithiothreitol monolayers on gold from dilute 2-propanol solution to form titanium-coordinated surfaces. The side view of a sessile drop of aqueous solution on the titanium-coordinated surface changed significantly as a function of time (corresponding to an apparent decrease in the contact angles), indicating that the surface became more hydrophilic as a result of its reaction with aqueous solution (i.e., the hydrolysis and polycondensation). The kinetics of this surface reaction was modeled, for the first time, based on the observed changes in the time-dependent contact angles. Pseudo-first-order kinetic parameters obtained showed an interesting two-step reaction feature when water was ...

Critical Surface Tension for Spreading in the Systems (Al‐Mg)/Graphite and (Cu‐O)/Sapphire

Abstract: According to Zisman and co-workers, in organic systems the cosine of the contact angle of a sessile drop increases with the decreasing surface tension of the drop at room temperature. The applicability of the Zisman relation to liquid metal-ceramic systems is discussed using the systems (Al-Mg)/graphite and (Cu-O)/sapphire. Also discussed is the significance of the critical surface tension for spreading, γc, in the systems where the surface tension of the liquid is greater than that of the solid substrate; γc is 230 dynes/cm for graphite at 720°C and 440 dynes/cm for sapphire at 1230°C.

Surface tensions of liquid Ag-Au-Cu alloys

Abstract: The surface tensions and the densities of liquid Ag-Au-Cu alloys have been determined by the sessile drop technique from their liquidus temperatures to 1108 °C. Surface tension minima which are indicative of ordering phenomena at the surface have been found in the limiting binaries Ag-Cu and Au-Cu and in the two pseudo-binary sections investigated which correspond to atomic ratios of gold to silver equal to 0.4 and 2.5. On the basis of thermodynamic data and surface tension isotherms, a graphical method to determine relative adsorptions and a numerical technique to calculate reduced adsorptions have been developed.