Thermally driven Marangoni surfers

We study auto-propulsion of a interface particle, which is driven by the Marangoni stress arising from a self-generated asymmetric temperature or concentration field. We calculate separately the long-range Marangoni flow v^{I} due to the stress discontinuity at the interface and the short-range velocity field v^{P} imposed by the no-slip condition on the particle surface; both contributions are evaluated for a spherical floater with temperature monopole and dipole moments. We find that the self-propulsion velocity is given by the amplitude of the "source doublet" which belongs to short-range contribution v^{P}. Hydrodynamic interactions, on the other hand, are determined by the long-range Marangoni flow v^{I}; its dipolar part results in an asymmetric advection pattern of neighbor particles, which in turn may perturb the known hexatic lattice or even favor disordered states.