On the question of rate-dependence of contact angles

Contact angles of different liquids on smooth and homogeneous films of Teflon AF 1600 were studied as a function of rate of motion of the three-phase line. For liquids with a dynamic viscosity of well below 10 (cP), neither advancing nor receding angles are influenced significantly by the rate of motion up to ∼12 (mm/min). On the other hand for more viscous liquids increasing the rate of motion causes the advancing angles to increase and the receding angles to decrease. Such dynamic contact angles may not be used in conjunction with the Young equation.