  The dynamics of active colloids is very sensitive to the presence of
boundaries and interfaces which therefore can be used to control their motion.
Here we analyze the dynamics of active colloids adsorbed at a fluid-fluid
interface. By using a mesoscopic numerical approach which relies on an
approximated numerical solution of the Navier-Stokes equation, we show that
when adsorbed at a fluid interface, an active colloid experiences a net torque
even in the absence of a viscosity contrast between the two adjacent fluids. In
particular, we study the dependence of this torque on the contact angle of the
colloid with the fluid-fluid interface and on its surface properties. We
rationalize our results via an approximate approach which accounts for the
appearance of a local friction coefficient. By providing insight into the
dynamics of active colloids adsorbed at fluid interfaces, our results are
relevant for two-dimensional self assembly and emulsion stabilization by means
of active colloids.
