Volume 215, number 1,2,3 CHEMICAL PHYSICS LETTERS 26 November 1993 Influence of inhomogeneity and fluctuations of supersaturation on heterogeneous nucleation B.Z. Gorbunov, E.L. Zapaclinsky zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC Novosibirsk State University, Pirogova street2. 630090 Novosibirsk, Russian Federation K.K. Sabelfeld and M. Ataev Computing Center, Lavrentjeva 6, 630090 Novosibirsk, Russian Federation Received 16 September 199 1; in final form 16 September 1993 The influence of fluctuations of vapour concentration on the heterogeneous nucleation rate is investigated. Computer calcula- tions based on the Monte Carlo method show this influence to be substantial at realistic values of non-thermodynamic fluctua- tions. Thermodynamic fluctuations do not affect the nucleation rate in the model under consideration. 1. Introduction Nucleation is an important factor in many phys- ical and chemical processes and is often used for practical purposes. The theory of nucleation rate is based on the law of local equilibrium, the kinetic theory of gases and the thermodynamic theory of fluctuations. The rate of heterogeneous nucleation (J) at constant temperature (T) and pressure de- pends on the critical value of Gibbs free energy of the new phase embryo formation AG*(S) [ 1,2], J=Bexp[ -AG*(S)/kT] , (1) where k is the Boltzmann constant, S is the super- saturation for nucleation from gases or supercooling for nucleation from liquids. Further, let us consider, more particularly, the nucleation from a mixture of two gases when the concentration of a nucleating component is much lower than that of another gas. This situation is typical for many applications, e.g. for water condensation in the atmosphere. The preexponential factor B is determined by the num- ber of molecular collisions with the embryo surface, monomer concentration and the form of the barrier near the maximum (Zeldovich factor [ 3 ] ) . The fac- tor B actually remains unchanged with varying ex- ternal conditions and substrate [ 2 1. Elsevier Science zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Publishers B.V. Expression ( 1) is derived for nucleation in a uni- form medium with time-independent characteris- tics. However, when the macroscopic system char- acteristics are the same, the local environment of a microscopic embryo may vary. This is determined by both thermodynamic and non-thermodynamic fluctuations, e.g. due to turbulence and convection as well as due to the depletion of a metastable me- dium. Hence, the pressure, temperature and super- saturation in the local environment of a growing em- bryo will depend on time and space. The fluctuations of temperature, pressure and concentration cannot but influence the nucleation rate. Supersaturation has an especially strong effect on the nucleation rate [ 21. Therefore, supersaturation fluctuations should be taken into consideration first of all. There are practically no publications that high- light the fluctuation influence on nucleation rate. Only in refs. [ 4,5 ] do the authors consider the role of the temperature fluctuations of a liquid droplet embryo for homogeneous nucleation. These fluctua- tions make droplets with different temperatures overcome the different activation barriers to pass to the state of a stable embryo. Supersaturation flue tuations might be expected to influence the nuclea- tion rate to a larger extent than temperature. The aim of the present Letter is to study the influence of su- 31