Abstract
We present experimental results concerning the advancing motion of drops of polymer solutions in the presence of controlled evaporation. We find that at high advancing velocities the classical Cox-Voinov law is verified, i.e. the advancing contact angle varies linearly with the capillary number. Below a critical velocity the contact angle increases as the advancing velocity is reduced. These results can be explained by taking into account the divergence of the rate of evaporation close to the contact line leading to an accumulation of polymer close to the edge of the drop. The induced local increase of the viscosity explains the increase of the contact angle. We show that the accumulation of polymer over a few nanometers is sufficient to slow down the contact line.
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