Experimental Investigation Of Evaporative Deposition Of Microparticles On PDMS Surface

When a sessile suspension droplet containing micro/nano-particles evaporates on a solid substrate,these particles will form a deposition on the substrate after evaporation.This phenomenon has found many applications in inkjet printing,medical diagnosis,biological sensor and microelectronics,and so on.Meanwhile,soft materials such as polydimethylsiloxane(PDMS)play an extremely important role in micro/nano-fluidics and micro/nano electromechanical systems.Therefore,evaporative deposition of microparticles on PDMS surface was experimentally investigated.This dissertation is made up of three main sections.(1)Evaporation of suspension droplets containing larger polystyrene microparticles on PDMS surfaces was experimentally investigated.It is found that the evaporation of ethanol/water mixture suspension droplets exhibits different characteristics from that of pure water.The settling time of microparticles was estimated and its theoretical value agrees well with the experimental one.Moreover,a compact monolayer deposition of microparticles was obtained for the case of low microparticle concentration,while a multi-layer deposition pattern for higher concentration.In addition,addition of 10% and 20% volume fraction of ethanol has no significant effec on the deposition pattern.(2)Evaporation of suspension droplets containing small polystyrene or silicon microparticles on PDMS surfaces was experimentally investigated.It is found that a central protrusion deposition is formed for droplets containing small polystyrene microparticles,and a ring-like deposition is formed for droplets containing small silicon microparticles,and addition of 10% and 20% volume fraction of ethanol has little influence on the deposition pattern.(3)Evaporation of suspension droplet of bi-dispersed polystyrene microparticles with different particle sizes on PDMS surface was experimentally investigated.It is found that a thin ring with an inner deposit is formed for droplets containing minimum microparticles for the case of low microparticle concentration,and an inner deposition is formed for the others.