Abstract
The properties of solid surfaces required for effective heterogeneous nucleation of ice from the vapor were investigated. Amorphous silicas were modified in various ways and tested in a cloud chamber. The surface properties of these substrates were then determined by gas adsorption techniques. The spatial distribution of the polar adsorption sites on the surface was examined by a steric hindrance method employing isopropanol adsorption. It was found that silicas heat treated in the presence of sodium chloride had satisfactory nucleating ability in the cloud chamber. Furthermore, the polar adsorption sites on these good nucleants were found to cover approximately half the available surface area and were distributed in clusters on a low-energy surface. Adsorption studies of several silver iodide preparations, on the other hand, showed the polar adsorption sites to be related to the impurity content of the substrates, which also yield polar sites in a hydrophobic matrix. A comparison of the nucleating properties of silver iodide preparations and modified silicas in water vapor and in bulk water indicated that good crystallographic match between substrate and ice is of primary importance, especially in bulk nucleation. In the absence of a favorable substrate structure, heterogeneous nucleation from the vapor is largely controlled by the water adsorption properties of the substrate. A partially hydrophilic substrate, which is an effective ice-nucleating agent in water vapor, is less effective in bulk water possibly because the site adsorption and clustering mechanism is rendered inoperative when the surface is covered with water.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call