Static contact angle hysteresis on smooth, homogeneous solid substrates |
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Authors: | Victor Starov |
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Affiliation: | 1. Department of Chemical Engineering, Loughborough University, Loughborough, LE 11 3TU, UK
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Abstract: | A theory of contact angle hysteresis on smooth, homogeneous solid substrates is developed in terms of shape of disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all contact angles, θ, in the range θ r?θ?θ a, which are different from the unique equilibrium contact angle θ?≠?θ e, correspond to the state of slow “microscopic” advancing or receding motion of the liquid if θ e ?θ?θ a or θ r?θ?θ e, respectively. This “microscopic” motion almost abruptly becomes fast “macroscopic” advancing or receding motion after the contact angle reaches the critical values θ?=?θ a or θ r?=?θ, correspondingly. The values of the static receding, θ r, and static advancing, θ a, contact angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining pressure isotherm. It is shown that an advancing contact angle of a droplet on a solid substrate depends on the drop volume and is not a unique characteristic of the liquid–solid system. The suggested mechanism of contact angle hysteresis has direct experimental confirmation. |
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