OU NanoLab/NSF NUE/Bumm & Johnson

The Kelvin Effect

Atoms
of liquid on the surface of a small droplet are held less tightly compared to atoms on a flat (bulk) liquid surface. High curvatures effectively reduce the coordination number of the
surface atoms making them easier
to evaporate. Thus the liquid has a
higher vapor pressure over small
liquid droplets compared to bulk liquid.
The effect of curvature on the
vapor pressure of liquids is the Kelvin effect.
*P* relative to the bulk *P**0* can be found using the Kelvin equation, show here for spherical surfaces of radius *r*.

Positive curvature:
liquid in drops has a higher vapor pressure that bulk.

Negative curvature:
liquid in pores has a lower vapor pressure than bulk.

The vapor pressure

The other parameters are:

*γ* the surface tension,

the molar volume of the liquid,

R the gas constant, and

*T* the absolute temperature.

the molar volume of the liquid,

R the gas constant, and