Meniscus

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Definition

Meniscus examples.
Sample menisci with water on the left (concave meniscus), and mercury on the right (convex meniscus). (Image from http://www.learnchem.net/)

A meniscus is a curvature in the surface of a fluid (e.g. water) as a result of molecular interactions with a container or object. If the meniscus is convex, then the molecules have a stronger attraction to themselves than the container or neighboring object (e.g. mercury which is non-polar thus not attracted to its glass container). If the meniscus is concave, then the molecules have a stronger attraction to the container or neighboring object than themselves (e.g. water which is polar and attracted to a glass container). With a concave meniscus, capillary action in a container will result in pulling the fluid upward to increase the contact area between the interfaces (energetically favorable).

References