Driving Adaptive Colloids Into Unsteady State Operation Via Push-Pull Effects

Unlike conventional colloids showing random mobility because of Brownian motion, active colloids contain nanomotors that translate chemical or physical triggers into directed movement. Whereas the acceleration of such particles works well, it is difficult to decelerate them by request. Driving and stopping functional colloids in dispersion is desirable for precise positioning, active matter therapeutics, or fundamental studies on how dissipative states influence emergent properties of particle ensembles. We developed nanoparticles comprising two independent mechanisms for propulsion, a chemical engine associated with a Janus-type modification of organosilica nanoparticles and a physical locomotion because of a superparamagnetic core inside these particles. Both triggers can be used independently to initiate the particles' directed and anisotropic movement. The magnetic forces can be tuned, most importantly with respect to the angle defining the chemical acceleration. Superposition and a boost state are adopted for a parallel alignment. However, when the magnetic field acting on the particles is turned to an antiparallel orientation, a rapid deceleration can be observed, and the colloids halt.