Evaporative deposition of mono- and bi-dispersed colloids on a polydimethylsiloxane (PDMS) surface

Abstract

Evaporative deposition of mono- and bi-dispersed colloids on a polydimethylsiloxane (PDMS) surface was studied. At particle concentrations of 0.02 and 0.08 wt%, 1.58 μm diameter polystyrene (PS) microparticles were uniformly distributed from mono-dispersed colloids. PS microparticles located at the edge of the deposition increased when the particle concentration increased to 0.32 and 1.28 wt%. Mono-dispersed colloids of 1.21 μm silica microparticles produced a ring-like deposition at particle concentrations ranging from 0.02 to 0.32 wt%. The width of the ring increased with increasing concentration and a mountain-like structure was produced at 1.28 wt%. The settling speed of 1.21 μm silica microparticles is 14 times greater than 1.58 μm PS microparticles resulting in easier settling of silica compared with PS microparticles. Experimental investigations show PS microparticles are dragged inward with the depinning contact line, and the outmost silica microparticles are pinned. The edge of the depositions of bi-dispersed colloids were made up of smaller microparticles and larger microparticles were found far from the edge due to capillary force.