A theory for the deliquescence of small particles

A theory is developed for the deliquescence of small particles that incorporates the effect of surface phenomena on the deliquescence process. The theory is based on rudimentary surface thermodynamics since we are primarily interested in the orders of magnitude of the various effects. Applying the theory to a generic crystal with properties similar to NaCl, in water vapor, we find that the surface tension has a significant effect for crystals with a radius smaller than 10(-5) cm. We suggest an experiment for the determination of the surface tension of soluble crystals that utilizes the deliquescence of these small particles. Serendipitously, such an experiment has just been performed by another group of authors. The qualitative analysis of this experiment should eventually be accompanied by a further development of the rigorous thermodynamic theory of solid surfaces. (C) 2000 American Institute of Physics. [S0021-9606(00)51042-3].