Binary Homogeneous Nucleation in Selected Aqueous Vapor Mixtures

The objective of this article is to give an overview of available experimental techniques and theoretical fundaments of the classical theories of homogeneous binary nucleation. The principles of the experimental setups are reviewed, ranging from low-nucleation-rate (≤103 nuclei/(cm3⋅s)) devices, i.e., thermal-diffusion cloud chamber, expansion chamber, over-nucleation pulse technique, and nozzle flow, to the condensation wave technique which is applied for the fastest nucleation rates (∼1015 nuclei⋅(cm3⋅s)−1). The theoretical description is based on the capillary approximation and takes into account the real properties of fluids (liquid mixtures) including the effects of non-equilibrium processes. A very important effect is associated with the surface tension dependence on the concentration of admixtures that can have a serious impact on the value of the nucleus formation energy. In the case of surfactants (i.e., molecules that can transiently bond with water through hydrogen bonding, e.g., alcohols) the nucleation work is decreased and for inorganic salts (hydrophobic molecules tend to be non-polar) the nucleation work is increased. The theoretical results are compared with the available experimental data. Also, the role of salts in power plant chemistry is discussed.