Ring stains in the presence of electrokinetic interactions

Abstract

In this paper, we delineate the consequences of electrokinetic interactions on the “coffee stain” effect, induced by the deposition of particles during drop evaporation. We consider evaporation of an electrolytic drop in contact with a charged substrate and probe the effects of electrical double layer formation at the drop-substrate interface on the dynamics of particles suspended inside the drop. We show that the simultaneous considerations of streaming potential and flow-actuation-mechanism-independent description of the evaporation flux and the depth average velocities result in an enhanced induced radial pressure gradient. As a result, the deposition speed of the particles in the disordered packing regime, occurring at the end of the lifetime of the drop [Marin et al., Phys. Rev. Lett. 107, 085502 (2011)], is greatly enhanced. This, in turn, is likely to signify an augmented degree of disordering in the evaporation-induced particle deposition.