The migration of liquid droplets in solids

Abstract

The migration of liquid H2O droplets in transparent KCl crystals was directly observed under various driving forces including thermal gradients, accelerational fields, and grain boundary and solid-liquid surface tensions. In all cases, it was found that the kinetics of attachment and detachment of atoms at the solid-liquid interface of the droplet is the factor which determines the migration rate and shape change on the liquid droplets. For example, with thermal gradients and accelerational fields, no droplet motion was observed below a critical droplet driving force because of these interface kinetics.The influence of interface kinetics was also demonstrated by examining shape changes of liquid droplets in KCl in two independent experiments. In the first experiment, it was shown that interface kinetics produce a flattening of the droplet perpendicular to its direction of motion. In the second experiment, already extended droplets were allowed to relax to their equilibrium shapes. Interface kinetics were found to retard the relaxation rate and to prevent large droplets from ever attaining an equiaxed shape.Finally, droplets were migrated into grain boundaries in KCl. From the critical thermal gradient or acceleration field required to free the liquid droplets from the grain boundary, the grain boundary energy of KCl was determined.