Meniscus (hydrostatic)
A meniscus (derived from the Greek Μηνίσκος, "Menískos" = crescent moon) is a bulge in the surface of a liquid . It can concave and convex are distinguished menisci (see figure); both go back to the interaction between the liquid and the surface of the adjacent wall:
- Concave menisci (Fig. A) arise e.g. B. between water and glass. Concave menisci in fine structures lead to capillarity . When reading a scale for measuring the liquid level, these meniscuses are read on the underside .
- Convex menisci (Fig. B) occur e.g. B. on mercury barometers ; they are read from the top .
Influencing variables
The contact angle of the meniscus surface on the wall is determined by the three interfacial tensions and is also often subject to hysteresis . The curvature in the further course is proportional to the local pressure difference, see Young-Laplace equation . In weightlessness , the curvature between homogeneous phases is constant, so the meniscus is spherical . In a gravitational field , the surface is far from the wall horizontally , wherein the width of the transition from the density difference between the fluids is dependent.
literature
- Walter J. Moore: Fundamentals of Physical Chemistry , ISBN 978-3110099416 , page 457.