is the surface tension of a liquid droplet stable?

lionelwang

Hi all,

Typically, we know that the surface tension for water is about 72mN/m at RT. so do this mean that the surface tension over the whole droplet is exactly the same? Moreover, we know that the Laplace pressure may be different over the whole droplet as the curvature in different parts might be different. How to explain those phenomena?
Waits for your wisdom, and thanks for any help!

Andy Resnick

the value you quote is for pure water- surface contamination, surfactants, or other solutes will drastically lower the value.

The curvature is allowed to vary with, for example, height in a gravitational field (hydrostatic pressure head). This does not change the interfacial energy, which is a property of the two phases.

The interfacial energy can support spatial gradients (Marangoni flow, for example) if there is a temperature or concentration gradient.

does that help?