Selective evaporation and contact line motions of evaporating ethylene glycol–water mixture droplets

Abstract

The evaporation of sessile binary mixture droplets with different volatile liquids is essential in various applications such as ink-jet printing, evaporators, fuel combustion, and medical diagnosis. The present study examined the evaporating characteristics of ethylene glycol–water binary mixture droplets (EGWBMDs) used for patterning the functional materials in inkjet printing. In particular, the study focused on selective evaporation and dynamic contact line motion. To this end, surface plasmon resonance and shadowgraph imaging methods were employed to measure the temporal ethylene glycol concentrations and droplet shapes, respectively. The results revealed that EGWBMDs evaporated in the depinning mode following the constant contact radius mode. The ethylene glycol concentrations increased with time; evaporation of water was dominant throughout concentration measurement, showing selective evaporation. In addition, there was a non-linear change in the volume of EGWBMDs due to the different volatility of each component. In particular, the volume variation changed rapidly at the initial stage. Next, the evaporation rates of water and ethylene glycol were quantitatively calculated based on the ethylene glycol concentration and droplet shape measurement. The evaporation rate obtained from the experiment was found to be consistent with the predictions obtained using a diffusion model, with maximum and average error rates of 6.14 and 2.56%, respectively.