8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P7.22Thu 811:10-14:00The dynamics of adsorption for anisotropic colloids nearliquid-liquid interfacesJoost de Graaf, 1 Marjolein Dijkstra, 1 and Rene van Roij 11 Utrecht University, Princetonplein 1, 3584 CC, Utrecht, NetherlandsWe present a numerical technique by which we have investigated the free energy of adsorptionfor anisotropic colloids upon contact with a flat liquid-liquid interface [1]. With this method wereduce the complex geometrical problem of studying non-spherical colloids at an interface byapproximating its surface with triangles, a procedure we refer to as triangular tessellation. Thefree energy of adsorption is comprised of surface and line tension contributions only, e.g., [2],for which we can establish the required contact areas and contact line lengths using triangulartessellation. Our method proves superior to traditionally used semi-analytic approaches whenit comes to general applicability and numerical stability. From our analysis we arrive at anorientation dependent free energy landscape, which acts as a potential of force on the colloid. Byusing simple dynamics we are able to study the process of adsorption for the colloid from initialcontact at the liquid-liquid interface to it reaching its equilibrium position [2]. We find that forellipsoidal particles there is only one equilibrium adsorption orientation, namely ’flat’ adsorption.For cylindrical colloids there may be a secondary minimum in the free energy landscape, whichcorresponds to the colloid adsorbing ’on-end’ or perpendicular to the interface. The presence ofthis minimum leads to unexpected dynamics and a large range of contact orientations for whichperpendicular adsorption is favored. We believe that it is possible to recover this behavior inappropriate experimental systems and that it occurs on a time scale which is accessible to usingcurrent microscopy techniques.[1] J. de Graaf, M. Dijkstra, R. van Roij, Phys. Rev. E 80, 051405 (2009).[2] F. Bresme and J. Fraudo, J. Phys. : Condens. Mat. 19, 375110 (2007).[3] J. de Graaf, M. Dijkstra, R. van Roij, J. Chem. Phys 132, 164902 (2010).22