A new method was proposed to estimate the rolling angle of a droplet on a superhydrophobic surface. Based on the relationship between the adhesion work and the force moment of the spherical droplet, a rolling angle model was established. For smooth surfaces, the equation we obtained is sin α ≥, and for rough surfaces, the equation is sin α ≥. The relationship between the rolling angle, the contact angle, and the surface structure was investigated. The equations we obtained revealed the factors that have important influences on the rolling angle, including the surface roughness, the trapped air, the mass of droplet, and the chemical composition of the surface. The simulation results showed that the rolling angle decreases with the increases of the contact angle, the surface roughness, the proportion of trapped air, the weight of the droplet, and the hydrophobicity of the surface material. These results agreed well with the most widely used explanation of other researchers.
The Flory-Huggins theory of polymer solutions combined with an evaporation process was employed to interpret the preparation mechanism of a super-hydrophobic surface by phase separation. The ternary phase diagram of a polymer/ solvent/ nonsolvent was calculated by using the solubility parameters of the components in the system. It indicated that with the increase of the nonsolvent fraction, the initial volume fraction of the polymer or the evaporation rate of the solvent, the evaporation time for phase separation would shorten and the phase separation rate would speed up. The polymer volume fraction in the dense phase would increase and the precipitating particles tended ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 to collide and aggregate, resulting in a rough, super-hydrophobic surface. Experimental results were in agreement with this principle of phase separation for preparing super-hydrophobic surfaces. Membranes of acrylic resin and fluorinated acrylic resin with rough surfaces were successfully obtained by the phase separation method.Especially, the water contact angle of the fluorine-containing acrylic resin with the rough surface was greater than 150°, which satisfied the requirement of super-hydrophobicity.
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