The Appearance Mechanism of the Permanent Stains on the Glass Plates (Part 3)

Evaporation of a Liquid Droplet of Aqueous Solutions of Slightly Soluble Electrolytes on the Glass Plates and Patterns of Their Deposits after Evaporation

Abstract

Evaporation of a liquid droplet of aqueous solutions of slightly soluble electlytes such as CaCO₃, CaSO₄, and KIO₄ and of concrete-soaked-rain water and concrete-soaked-distilled water on untreated and surface-treated glass plate has been investigated through the measurement of bottom length and contact angle of the liquid droplet against time. The deposition of the solute after evaporation has also been investigated. The contact angle decreased at a constant bottom length during the evaporation of a droplet on untreated glass plates. The solute deposited on the edge of the droplet and showed a caldera-like ring after complete evaporation. On the other hand, contact angle decreased to a limited value θ_R at a constant length of bottom of a droplet on the hydrophobic surface of glass plate with low surface energy and afterwards the length of bottom of a droplet decreased at a constant contact angle, θ_R during its evaporation. A crystalline agglomerate smaller than that of the initial liquid droplet was deposited after complete evaporation.