Estimation of thermophysical properties of a large polar molecule and application to homogeneous nucleation of l‐menthol

The classical Becker–Doering theory has predicted to within 5% the critical supersaturations required for homogeneous nucleation for more than a dozen molecules. These successes have prompted us to investigate whether the classical theory can predict the experimental results for more extreme cases, i.e., high temperature measurements on large, polar molecules with hydrogen‐bonding functional groups, like l‐menthol. It is therefore the purpose of this paper (1) to report high temperature diffusion cloud chamber measurements on 1‐menthol vapor; (2) to present the thermophysical properties, data or calculated values, required for (a) the experiment, i.e., the mass and heat flux equations, (b) the theory, and (c) the film correction; and (3) to compare the predictions of the Becker–Doering theory with the experimental results. Critical supersaturations, measured over the temperature range 41–100 °C, are about 7% higher than those predicted by the theory. Applying a film correction to the raw data brings the experimental envelope to within 5% of the theoretical curve. On the basis of this success the classical theory can indeed be extended to include high temperatures and unique molecules. However, the experimental results lie above the theory curve, indicating that menthol may be somewhat associated in the vapor phase. Accurate experimental supersaturations can be obtained for a molecule even though its thermophysical properties are scarce. Except for the vapor pressure, all the properties of menthol used in the mass and heat flux equations are calculated by reliable theoretical or empirical estimation methods. Varying each property by an amount equal to the error inherent in the corresponding estimation method has an insignificant effect on the supersaturation profile in the chamber. In fact, neglecting the film correction is a larger source of experimental error than estimating all the properties (except the vapor pressure) required to solve the mass abd heat flux equations. Since the vapor pressure is critical to the experimental results, one set of self‐consistent vapor pressure data for menthol, measured over the range 30–175 °C, is needed. Given a more accurate vapor pressure expression, we can determine to what degree menthol is associated in the vapor