Experimental study on the characteristics of temperature dependent surface/interfacial properties of a non-ionic surfactant aqueous solution at quasi-thermal equilibrium condition

Abstract

The surface/interfacial properties of liquid at elevated temperatures are fundamental issues for wide applications where the surface force matters. The dynamic characteristics of wetting behavior and surface tension (ST) of surfactant solutions remain unclear at thermal equilibrium, especially at high temperature. Utilizing a quasi-thermal equilibrium setup, the temperature dependence of the surface/interfacial properties of liquids (ultra-pure water and aqueous surfactant solutions) at temperature ranging from 10 to 90 °C (1 atm) are studied, by the sessile drop method and pendant drop method, respectively. A decreasing trend of the initial ST and contact angle (CA) is observed with the increase of temperature. During evaporation, the increase of the local relative humidity around the droplet has a crucial influence on CA. The obtained ST and CA are based on the thermodynamic model with modified coefficients, which can well describe the general trends for different temperatures and concentrations. For the ultra-pure water, the droplets will be pinned suddenly on the heating surface, until a sudden contraction occurs with evaporation. However, the surfactant-laden droplet shows different dynamical behaviors from ultra-pure water. Three different stages, named spreading-controlled Stage I, evaporation-controlled Stage II, and depinning-controlled Stage III are found for the dynamic evolution of surfactant-laden droplet. In what follows, the different droplet behaviors are also analyzed for surfactant solution and ultra-pure water.