Surfactant-Enhanced Spreading on Solids: Roles of the Surface Tension Gradient, Spreading Contact Angle, and Viscosity

Despite its important technological applications, surfactant-enhanced (spontaneous) spreading on a solid surface and how to optimize it on surfaces with different wettabilities are not well understood. Spontaneous spreading involves a surface tension gradient (Marangoni stresses), which enhances spreading over a large area. Experimental observations reveal that the spreading rate and surfactant concentration have an optimum substrate wettability of 60 ± 5° (Hill, R. M.