Is the surface tension of a liquid droplet stable?

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The surface tension of a liquid droplet, such as water, is generally uniform at around 72 mN/m, but variations can occur due to factors like surface contamination or the presence of surfactants. The Laplace pressure differs across the droplet due to varying curvature, which can be influenced by gravitational effects. While the interfacial energy remains constant, spatial gradients can lead to phenomena like Marangoni flow, driven by temperature or concentration differences. Understanding these dynamics is crucial for explaining the stability of surface tension in droplets. Overall, the surface tension is not strictly stable across the droplet due to these influencing factors.
lionelwang
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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!
 
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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?
 

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