Interferometric measurement of co-operative evaporation in 2D droplet arrays

The evaporation dynamics of multiple droplet arrays is important in inkjet printing and spray coating, where co-operative "shielding " effects increase the overall evaporation time. However, current measurement methods provide limited information on how individual droplets contribute to the overall dynamics. In this work, we present a simple interferometric technique for precise measurements of droplet evaporation rates, which is not possible via traditional approaches. We validate the technique on a single droplet. We then extend our analysis to ordered and random 2D arrays of droplets. We demonstrate that the evaporation rate is highly dependent on the position of the droplet within the array and its confinement. The more confined droplets exhibit lower evaporation rates. Our results of ten different configurations and well over 100 droplets are in good quantitative agreement with a recent analytical model of co-operative evaporation rates. Our approach opens up possibilities for studies of collective evaporation effects, including in areas of current importance such as sneezes and exhaled breath.