Sequential tasks performed by catalytic pumps for colloidal   crystallization
  Gold-platinum catalytic pumps immersed in a chemical fuel are used to manipulate silica colloids. The manipulation relies on the electric field and the fluid flow generated by the pump. Catalytic pumps perform various tasks, such as the repulsion of colloids, the attraction of colloids, and the guided crystallization of colloids. We demonstrate that catalytic pumps can execute these tasks sequentially over time. Switching from one task to the next is related to the local change of the proton concentration, which modifies the colloid zeta potential and consequently the electric force acting on the colloids. 
Ali Afshar Farniya, Maria J. Esplandiu, Adrian Bachtold
cond-mat.soft cond-mat.mes-hall physics.flu-dyn