Capillary Forces between Chemically Different Substrates

Abstract

Motivated by experimental results, we present numerical and analytical calculations of the capillary force exerted by a capillary bridge spanning the gap between two parallel flat plates of asymmetric wettability. Depending on whether the sum of the two contact angles is smaller or larger than 180 degrees, the capillary force is either attractive or repulsive at small separations D between the plates. In either cases the magnitude of the force diverges as D approaches zero. The leading order of this divergence is captured by an analytical expression deduced from the geometry of the meniscus of a flat capillary bridge. The results for substrates with different wettability reveal an interesting behavior: with the sum of the contact angles fixed, the magnitude of the capillary force and the rupture separation decreases as the asymmetry in contact angles is increased. In addition, we present the rupture separation, i.e., the maximal extension of a capillary bridge, as a function of the contact angles. Our results provide an extensive picture of surface wettability effects on capillary adhesion.

Comparative study of the fluid viscosity in tarsal hairy attachment systems of flies and beetles

“…Interface 11: 20140752 total attractive capillary force F c ¼ F L þ F st has two components: F L , the contribution from the Laplace pressure (the pressure difference inside and outside the capillary bridge); and F st , the contribution arising from the surface tension acting along the perimeter [43]. However, for small separations h, the contribution of the Laplace pressure to capillary force is large, when compared with the contribution of the surface tension [44]. Because we are interested in the contact formation, where h becomes very small, we estimated the capillary force between parallel plates for small h by…”

Attachment ofGalerucella nymphaeae(Coleoptera, Chrysomelidae)to surfaces with different surface energy

“…The similarity of the trend in larval and adult G. nymphaeae regardless of the number of contacts might be evoked by a physical principle (De Souza et al, 2008b). De Souza et al calculated the strength of capillary forces between two surfaces that have different contact angles and state that if the sum of the two contact angles is constant, the forces decrease with increasing asymmetry in the two contact angles.…”

Dynamics of freely moving plates connected by a shallow liquid bridge

“…The magnitude of the capillary force acting at the triple phase contact line scales as $ cr 0 and is negligible in comparison with the $ cr 0 =e force associated with the capillary pressure for the case of shallow liquid bridges. 20 Thus, the force acting in the triple phase contact line is not included in the current approximation. For a freely moving solid body, the force applied by the liquid bridge is balanced by external and body forces acting on the solid body and the rate of change of momentum.…”

“…0, and under the above assumptions, the shape of the liquid surface in leading-order is part of a circular arc. The curvature at the liquid-gas interface is thus obtained from geometric relations 20 …”