(296a) Chemical Sailing

We consider a nonspherical catalytic particle with a uniformly distributed catalyst over its surface in a suspension of reactant particles. The first kind chemical reaction takes place at the surface of the catalytic particle.

Our calculations demonstrate that the nospherical particle could create inhomogeneity in the reactant concentration, which, in turn, emerges a gradient of the osmotic pressure pushing the particle. For a small distortion of the surface from the spherical one, the effect is quadratic in nonsphericity rather than linear one, as reported by Wei and Jan (JFM, 2010). For a finite nonsphericity numerical calculations by the boundary element method were performed. Both analytical results and numerics show that the maximum velocity of the self-propulsion is attained, when the characteristic times of chemical reaction and diffusion of reactant particles are comparable; in the limiting cases of slow and fast reaction the effect vanishes.

We also consider a motor, which uniformly emits product particles at its surface; the self-propulsion takes place as well, but in the opposite direction in comparison with the case of suspension of reactant.

An analysis of the optimal shape to provide the maximal velocity of self-propulsion is carried out as well. We show that no saturation is possible – the larger area is, the larger velocity can be reached. However, the optimal shape should contain the concave segments, e.g. a thin hemisphere. In this case the velocity is independent of the hemisphere thickness and is determined by its radius only.