Effect of Adsorbed Water on the Spreading of Organic Liquids on Soda‐Lime Glass

The spreading behavior and equilibrium contact angle, θ, of organic liquids on soda‐lime glass surfaces were observed at relative humidities (rh) varying from 1 to 95%. Increasing rh increased θ for many nonhydrophilic liquids on glass; no comparable effects occurred with nonadsorptive solid surfaces. The decrease in wettability of the glass with increasing rh resulted from the physical adsorption of a surface layer of water molecules sufficient to convert the normally high‐energy glass surface into one that behaves as a low‐energy surface, i.e. a surface with a low critical surface tension for spreading, γ c , toward nonhydrophilic liquids. As the thickness of the adsorbed water layer increased, glass behaved like a surface with progressively decreasing γ c , approaching that of bulk water. These results are discussed in relation to the effect of moisture on the spreading or adhesion of resins to glass and other hydrophilic solids.