Influence of particle surface roughness on the behaviour of Janus particles at interfaces

We demonstrate that it is of critical importance to prepare Janus particles with a high degree of control over the surface roughness. To elucidate information regarding the behaviour of Janus particles at an interface, we have used a gel-trapping technique coupled with metal evaporation to prepare Janus particles. Since one face is covered in gold, direct observation of the different faces at air–water and water–oil interfaces can be carried out. For particles prepared by this gel-trapping technique, the interface between hemispheres is rough and this leads to the observed orientation being random. We show that for these particles the surface roughness can dominate over the surface chemistry with regards to particle orientation. This has important implications for many of the synthetic routes towards Janus particles suggesting that, for optimum performance, it is necessary to prepare particles where the surface roughness is kept to a minimum.