Contact line dynamics on a pseudo-brush

Polymer~ brushes are nanometric layers of polymers that are attached to a solid surface. They are well-known for strongly modifying the mechanical properties of the surface. Although friction and slippage experiments have been performed on such systems [1], the impact of brushes on wetting dynamics has not yet been investigated. We report measurements of contact line dynamics of simple liquids over so-called pseudo-brushes adsorbed on silicon. We will show that this system exhibits (i) a surprisingly low hysteresis, a feature of great utility when studying the impact of added defects on the contact angle hysteresis, and (ii) a specific contribution to the dissipation, which is localized at the contact line, in addition to the viscous dissipation in the liquid wedge. The pseudo-brush contribution can be isolated from the total dissipation [2] and a simple model is used to explain the role of the pseudo-brush.\\[4pt] [1] C. Cohen, F. Restagno, C. Poulard, L. L\'{e}ger, Soft Matter 7, 8535 (2011)\\[0pt] [2] G. Delon, M. Fermigier, J.H. Snoeijer, B. Andreotti, J. Fluid Mech. 604, 55-75 (2008)