Fig. 2.

Protocol for the preparation of the Janus pillars. In the third step, the solution containing polystyrene particles is gently deposited in the air water interphase (i) of a Langmuir trough filled with water (b). The Teflon barriers are compressed at a low rate (ii) until the colloids self-assemble in a hexagonal arrangement. The process is monitored following the surface pressure vs covered area plot recorded by using a Wilhelmy plate connected to a force detector (a). After lowering the level of water, the packed colloids are gently deposited on the surface mainly by van der Waals forces.