The wetting problem of fluids on solid surfaces: Dynamics of lines and contact angle hysteresis

In 1805, Young was the first who introduced an expression for contact angle in static, but today, the motion of the contact-line formed at the interse ction of two immiscible fluids and a solid is still subject to dispute. By means of the new physical concept of line viscosity, the equations of motio ns and boundary conditions for fluids in contact on a solid surface togethe r with interface and contact-line are revisited. A new Young-Dupre equation for the dynamic contact angle is deduced. The interfacial energies between fluids and solid take into account the chemical heterogeneities and the so lid surface roughness. A scaling analysis of the microscopic law associated with the Young-Dupre dynamic equation allows us to obtain a new macroscopi c equation for the motion of the contact-line. Here we show that our theore tical predictions fit perfectly together with the contact angle hysteresis phenomenon and the experimentally well-known results expressing the depende nce of the dynamic contact angle on the celerity of the contact-line. We ad ditively get a quantitative explanation for the maximum speed of wetting (a nd dewetting).