Nucleation probability in binary heterogeneous nucleation of water–n-propanol vapor mixtures on insoluble and soluble nanoparticles

Abstract

Nucleation probabilities for binary heterogeneous nucleation have been measured quantitatively. Heterogeneous nucleation of binary n-propanol-water vapor mixtures on partially soluble 6.9-nm NaCl particles and on nonsoluble oxidized and nonoxidized 8-nm Ag particles at a constant nucleation temperature of 288 K (NaCl) or 285 K (Ag) has been investigated experimentally and theoretically. An expansion chamber was applied to generate supersaturated vapor mixtures. Number concentrations of particles activated to condensational growth were determined optically for various vapor phase activities at constant temperature. Nucleation probabilities have been measured as functions of the vapor phase activities for several n-propanol-water vapor mixing ratios. Beyond certain vapor phase activities a sharp onset of heterogeneous nucleation was observed both for NaCl and for Ag particles. For insoluble particle surfaces the theoretical slopes of the nucleation probability versus vapor phase activity curves were found to be somewhat steeper as compared to the experiment. On the other hand, for soluble particles the experimental slopes were found to be in satisfactory agreement with theory. The onset of the nucleation process is defined at an activity value where 50% of the particles were activated to condensational growth. Onset activities were obtained for various mixing ratios of the binary vapor mixtures. In the case of NaCl nuclei for n-propanol rich mixtures, the heterogeneous nucleation calculations based on a thermodynamically consistent version of Fletcher theory and an experimentally determined contact angle provide a reasonable approximation of the experimental data. However, it appears that the Fletcher theory is not applicable in the region of transition from n-propanol rich to water rich mixtures. Based on the Köhler theory of activation of soluble particles, a theory was formulated accounting for the presence of two condensable vapors and limited solubility of NaCl in water-propanol liquid mixtures. This approach provides a satisfactory description of the transition from activation of soluble particles to nucleation of vapors on insoluble particles. In the case of silver particles Fletcher theory with macroscopic experimental contact angles as well as with contact angle zero results in strong deviations from experimental data. A significant improvement was achieved by introducing fit contact angles, which are substantially lower than the macroscopic experimental values and may be considered as approximate values of the microscopic contact angles.

Effect of Working Fluid on Sub-2 nm Particle Detection with a Laminar Flow Ultrafine Condensation Particle Counter

“…A similar sign dependence of activation efficiencies was also observed in previous studies using a different technique (Winkler et al 2006b(Winkler et al , 2008. In this technique the saturation ratio inside the expansion chamber is precisely controlled, and the light scattered off from the grown droplets within a viewing volume are measured (Wagner 1985;Wagner et al 2003). The activated fraction is considered 100% when the light scattering signals reached a plateau; therefore, the method does not determine the activation efficiency absolutely by independently measuring the total concentration of particles within the viewing volume before and after the activation; however, the technique can precisely determine the saturation ratios where the activation of electrically charged and neutral particles occurs SUB-2 NM PARTICLE DETECTION WITH LAMINAR FLOW CPC 91 and is able to determine the sign dependence of activation more rigorously.…”

“…It is also evident that the activation efficiencies depend on the material of the test particles. Previous theoretical studies indicate the activation efficiencies are strongly affected by the solubility of test particles in the working fluid and the wettability of particle surface by the working fluid vapor (Scheibel and Porstendöerfer 1986;Wagner et al 2003;Kulmala et al 2007).…”

Commentary on cloud modelling and the mass accommodation coefficient of water

“…carried out experiments on the growth rates of water droplets observing growth kinetics in an expansion cloud chamber system. They studied liquid droplets nucleated on Ag particles and growing due to condensation of supersaturated water vapour using the experimental system presented in detail by Wagner et al (2003). In the experiments,the supersaturations were on the order of 30-40%, and droplet growth rates on the order of 10 µm/s.…”

An adsorption theory of heterogeneous nucleation of water vapour on nanoparticles

“…Chen et al, 1998Chen et al, , 1999Winkler et al, 2008); however, the selected systems were the only ones for which we found both adsorption and contact angle data so that the parameters of the theory could be determined. Note that both Porstendörfer et al (1985) and Wagner et al (2003) refer to silver nanoparticles instead of Ag 2 O. Nevertheless, the surface of silver nanoparticles can be rapidly oxidized if the carrier gas (compressed air in the experiments of Porstendörfer et al, 1985) contains trace amounts of hydrogen sulfide.…”

“…The adsorption parameters are given in Table 1. Wagner et al (2003) reported the contact angle of water on silver (which we assume to have a surface coating of Ag 2 O) to be 90 • . With such a hydrophobic surface, one would not expect strong multilayer adsorption, and the strong Kelvin effect of the adsorbed droplets should cause the data to fall on a curved line in an FHH plot rather than being linearly aligned (see Laaksonen, 2015).…”