Temperature Dependence of Contact Angles of Water on a Low Energy Surface under Conditions of Condensation and at Reduced Pressures

Abstract

SEVERAL workers have recently examined the effect of temperature on the wetting of solids, and Petke and Ray¹ have shown that there is extensive disagreement about both the sign and magnitude of the dependence of the contact angle with temperature. Fowkes and Harkins² reported a temperature coefficient of +0.06 degree °C⁻¹ for water/graphite and water/ paraffin systems whereas Adam and Elliott³ found no temperature effect when examining water droplets on solid hydrocarbons. Neumann⁴ showed that the contact angle of water on a polyamide increased with temperature, but Phillips and Riddiford⁵ reported that the contact angle of water on a siliconed glass surface was essentially constant for a temperature range of 70° C. Sutula et al.⁶ gave a temperature coefficient of + 0.03 degree °C⁻¹ for water on a fluoropolymer, but Padday⁷ suggested coefficients of − 0.15 degree °C⁻¹ and +0.55 degree °C⁻¹ for advancing and receding contact angles on paraffin wax at temperatures of 20° C to 40° C. Petke and Ray¹ themselves showed that advancing contact angles for water on a series of low surface energy polymers were all negative (−0.04 degree °C⁻¹ to −0.14 degree °C⁻¹) and that the receding contact angles could take positive or negative values (−0.04 degree °C⁻¹ to +0.06 degree °C⁻¹). For a ‘Teflon’ surface Neumann⁸ observed no variation of contact angle from room temperature to 60° C for water at atmospheric pressure, although coefficients of −0.3 degree °C⁻¹ and −0.15 degree °C⁻¹ were reported for the systems butyl chloride and n-heptane and butyl alcohol. Phillips and Riddiford⁹ also quoted contact angle invariance with temperature within the range 0° to 60° C for the ‘Teflon’–water system at a pressure of 1 atmosphere.