Hysteresis of Contact Angle of Sessile Droplets
Department of Chemical Engineering, Loughborough University, LE11 3TU, UK.
Corresponding author. E-mail: V.M.Starov@lboro.ac.uk
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 θr<θ<θa, which are different from the unique equilibrium value θe, correspond to the state of slow “microscopic” advancing or receding motion of the liquid if θe<θ<θa or θr<θ<θe, respectively. This “microscopic” motion almost abruptly becomes fast “macroscopic” advancing or receding motion after the contact angle reaches the critical values θa or θr, correspondingly. The values of the static receding, θr, and static advancing,θa, contact angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining/conjoining pressure isotherm. It is shown that both advancing contact and receding contact angles of a droplet on a solid substrate depends on the drop volume and are not a unique characteristic of the liquid-solid system. The suggested mechanism of the contact angle hysteresis of droplets has direct experimental confirmation.
Mathematics Subject Classification: 76B45 / 76D45 / 76D05 / 76R50 / 82D15
Key words: contact angle hysteresis / surface forces
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