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This occurs between water and glass. Water-based fluids like sap, honey, and milk also have a concave meniscus in glass or other wettable containers. Conversely, a convex meniscus occurs when the adhesion energy is less than half the cohesion energy. Convex menisci occur, for example, between mercury and glass in barometers [1] and thermometers.
Because of its high cohesion and low adhesion to the glass, mercury does not spread out to cover the bottom of the flask, and if enough is placed in the flask to cover the bottom, it exhibits a strongly convex meniscus, whereas the meniscus of water is concave.
In addition, the same attractive or repulsive effect can be observed between objects and the wall of the container. Once again there are two possibilities: the interface between the liquid and the container wall is either a concave or a convex meniscus. Buoyant objects will be attracted in the case of a concave meniscus and repelled for convex.
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to float on a water surface without becoming even partly submerged.
At the meniscus interface, due to the surface tension, there is a pressure difference of =, where is the pressure on the convex side; and is known as Laplace pressure. If the tube has a circular section of radius r 0 {\displaystyle r_{0}} , and the meniscus has a spherical shape, the radius of curvature is r = r 0 / cos θ {\displaystyle r ...
Meniscus may refer to: Meniscus (anatomy) , crescent-shaped fibrocartilaginous structure that partly divides a joint cavity Meniscus (liquid) , a curve in the upper surface of liquid contained in an object
As water has strong dipole characteristics, whilst the membrane fabric is non-polar, the membrane material is not wetted by the liquid. [5] Even though the pores are considerably larger than the molecules, the high water surface tension prevents the liquid phase from entering the pores. A convex meniscus develops into the pore. [6]
The capillary length will vary for different liquids and different conditions. Here is a picture of a water droplet on a lotus leaf. If the temperature is 20 o then = 2.71mm . The capillary length or capillary constant is a length scaling factor that relates gravity and surface tension.