![]() Teflon and paraffin are virtually nonwettable by water and some other liquids. For instance, liquid alkaline metals and cryogenic liquids wet metal surfaces nearly absolutely and the angle θ approaches zero. The wetting angle depends on the liquid and the surface it is in contact with. According to the Young equation,įigure 1. Solid surface in contact with gas and liquid gases. An angle θ made by the tangent to the liquid surface and the solid surface, known as a wetting angle, is determined by the balance of forces within the surface tension. Interaction of surface tension forces at the liquid-gas σ 12, liquid-solid σ 13, and gas-solid σ 23 interfaces is responsible for a curved area of the liquid surface (meniscus) near the solid. This state corresponds to a stable equilibrium of the fluid since a sphere has the minimum surface and, consequently, the minimum surface energy.Īs shown in Figure 1, when the liquid (1) comes in contact with the gas vapor (2) and the solid (3), the shape of the free liquid surface depends on wetting. In the simplest case when the external forces are absent, e.g., under weightlessness conditions, a limited fluid volume takes the shape of a sphere due to surface tension forces. ![]() For a plane interface, H=0 and p σ=0.Ĭapillary phenomena include various cases of equilibrium and flow of fluid surface under the action of surface tension forces and of external forces, primarily gravity. ![]() The pressure is higher in the phase to which the concavity of the interface is presented. Where σ 12 is the surface or interfacial tension (see Surface and Interfacial Tension) on the boundary between phases 1 and 2, p 1 and p 2 are the pressures in the phases. ![]()
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