Hydrodynamic interactions between two side-by-side Janus spheres

Abstract

Janus spheres are heterogeneous amphiphilic particles having partially slippery and partially sticky surface. As a result, hydrodynamic forces such as drag and lift on a Janus sphere are different from those on a homogeneous sphere. Several applications of Janus particles require high particle concentration in a continuous fluid medium making the interactions between them inevitable. Therefore, in this study three-dimensional flow around two Janus spheres held fixed relative to each other with the line connecting their centres normal to a uniform fluid stream, is investigated computationally at Reynolds numbers ranging from 0.1 to 50. The dependence of lift and drag coefficients on the separation distance between the two Janus spheres is studied. Two cases, (A) sticky hemispheres facing each other and (B) slippery hemispheres facing each other are considered. While for Case A, the spheres repel each other for all the separation distances studied, a cross-over from repulsion to attraction regime with the increase in Reynolds number is observed for Case B. Correlations are proposed for drag at various separation distances for both the orientations.