Heterogeneous Vapor-to-Liquid Nucleation of Water on Individual Glass Particles

An apparatus that combines upward thermal diffusion with electrostatic levitation was used to study vapor-to-liquid nucleation on individual micron-sized clean glass particles. A vertical gradient in relative humidity was established in the chamber with the lower region being undersaturated while the upper region was supersaturated. Particles underwent vertical oscillatory motion when a fixed electric field was applied in excess of that required simply to achieve levitation. The period and the amplitude of oscillation were measured at varying electric field intensities. The balancing electric potential for several particles at a given elevation was also measured. The critical supersaturation, the radius, and the electric charge of the particles were then determined by using the equations of motion and condensational growth. Variations in the surface charge density for soda-lime glass particles of nominally the same size largely accounted for the particle-to-particle variability in the critical supersaturation. Cycle-to-cycle variations were also examined. For most particles, these variations were small with no general trends.