Evaporation Of Ethanol/Water Mixture Droplets On Pillar-like PDMS Surface

Polydimethylsiloxane(PDMS)as the representative of the soft lining material plays a very important role in micro-nano processing technology,micro-nano mechanical and electrical system and micro-nano fluid system and other fields.At the same time,droplets are widely used in these systems as a carrier.Therefore,this paper takes the evaporation of ethanol-water mixture droplets on the surface of microstructure PDMS as the starting point to reveal the wettability and evaporation characteristics of the mixture droplets on the surface of microstructure PDMS.The specific work is as follows:(1)the wettability and evaporation characteristics of five ethanol-water mixtures on the surface of PDMS were analyzed,and it was found that the addition of ethanol changed the wettability of the droplet.Taylor expansion was used to calculate the excess free energy in the droplet evaporation process,and qualitatively explained why the droplet expansion of 25% and 50% ethanol-water mixture occurred in the last stage of evaporation.(2)the wettability and evaporation characteristics of four ethanol-water mixtures on the surface of cylindrical PDMS were analyzed.It was found that when the ethanol concentration of the mixture droplet was 0% and 25%,the quadratic power of dimensionless volume decreased almost linearly,but when the ethanol concentration increased to 50% and 75%,it showed a nonlinear change.It was also explained that the duration of the CCR phase of the droplet evaporation process on the pitted PDMS surface was longer than on the flat PDMS surface.(3)the wettability of four ethanol-water mixtures on pitted PDMS was analyzed.The changes in volume,contact radius and contact Angle at the corresponding stages were derived by comparing the evaporation behavior of ethanol-water droplets on the flat PDMS surface and on three pitted PDMS surfaces with different spacing.It was found that the pit structure had less influence on evaporation when the concentration of ethanol was low,while the pit structure had more influence on evaporation when the concentration of ethanol was high.