Homogeneous vapor phase nucleation of a large fatty acid: Stearic acid

Publisher Website
Google Scholar
Abstract
Homogeneous nucleation measurements are made on stearic acid vapor using a diffusion cloud chamber and the resulting critical supersaturations compared with the predictions of the classical Becker‐Doering theory. These measurements are difficult because of the unusually low pressures and high temperatures required to investigate the involatile stearic acid molecule. The results indicate a definite discrepancy between theory and experiment. Measured critical supersaturations lie 27% above the theory at the lowest temperature and 10% below the theory at the highest temperature. Calculations show that part of this increase in experimental critical supersaturation at the lower temperatures could be due to association in the vapor. There are two additional findings: (1) The usual top plate boundary condition must be corrected for molecules, such as stearic acid, which have low equilibrium vapor pressures in the temperature range of interest. (2) The growth times for stearic acid droplets are at the limits that can be tolerated in a feasible diffusion cloud chamber experiment. This study suggests an area for future investigation. Once the association equilibrium constant for stearic acid vapor is known, the data presented here can be reanalyzed and the extent to which the dimer stabilizes the supersaturated vapor determined.