CONDENSATION OF SUPERSATURATED VAPORS OF HYDROGEN-BONDING MOLECULES -ETHYLENE-GLYCOL, PROPYLENE-GLYCOL, TRIMETHYLENE GLYCOL, AND GLYCEROL

The critical supersaturations required for the homogeneous nucleation (rate of 1 drop cm(-3) s(-1)) of ethylene glycol, propylene glycol, tr imethylene glycol and glycerol vapors have been measured over wide tem perature ranges (e.g., 280-400 K) using an upward thermal diffusion cl oud chamber. At lower temperatures the experimental nucleation rates a re much higher than the predictions of the classical nucleation theory . Glycerol shows the best agreement between experiment and theory in t he temperature range of 340-370 K. An apparent increase in the critica l supersaturation of glycerol is observed with increasing carrier gas (helium) pressure and this effect is more pronounced at lower temperat ures. The results from corresponding states and scaled nucleation mode ls indicate that the nucleation behavior of glycerol is quite differen t from other glycols. Glycerol requires higher critical supersaturatio ns compared to the other glycols at the same reduced temperatures. Thi s implies quite small critical clusters for glycerol (20-50 molecules) in the temperature range 300-380 K. The discrepancy between experimen t and theory at lower temperatures may be explained by considering tha t the surface tension of the critical clusters is lower than the bulk surface tension. It is, however, surprising that a Tolman type correct ion for the curvature dependent surface tension could be applicable fo r such small critical clusters. Further theoretical work is required i n order to fully understand the observed higher nucleation rates at lo wer temperatures of glycols and glycerol. (C) 1996 American Institute of Physics.