Phototaxis of active colloids by self-thermophoresis.

Phototaxis usually refers to the ability of a motile micoorganism to move directionally within a light gradient, which is important for microorganisms to gain energy or avoid damage. Here, we show that an active Janus particle driven by self-thermophoresis from light heating is able to exhibit significant phototactic motion by means of mesoscale dynamics simulation. Depending on the particle-fluid interactions, the active particle can move along or against the light gradient, corresponding to positive or negative phototaxis, respectively. We find that the phototaxis of the active colloid is determined by various mechanisms, including alignment (polarization) of the particle to the light gradient, orientation-dependent motility and spatially inhomogeneous motility. Our results shed light on the phototactic behavior of artificial active colloids and open up a new possibility to design photo-responsive micromachines.