3. Influence of temperature on surface tension

As the temperature of a liquid rises, the thermal agitation of the molecules increases. This makes it easier for them to leave the surface and move inwards. Since the force attracting molecules inwards is surface tension, it should decrease as temperature rises. This is generally what we observe. Most of the positive coefficients reported in the literature can be attributed to impurities. As the interface disappears at the liquid-gas critical point, the surface tension is zero.

Surface tension is therefore greater the closer the temperature at which it is measured is to the temperature of the triple point. The simplest relationship assumes that σ is a decreasing linear function of T