Self-propelled nanodimer bound state pairs

A pair of chemically powered self-propelled nanodimers can exist in a variety of bound and unbound states after undergoing a collision. In addition to independently moving unbound dimers, bound Brownian dimer pairs, whose center-of-mass exhibits diffusive motion, self-propelled moving dimer pairs with directed motion, and bound rotating dimer pairs, were observed. The bound pairs arise from a solvent depletion interaction, which depends on the nonequilibrium concentration field in the vicinity of dimers. The phase diagram reported in the paper shows regions in monomer interaction energy-diameter plane where these bound and unbound states are found. Particle-based simulations and analytical calculations are used to provide insight into the nature of interaction between dimers that gives rise to the observed bound states.