Vapour field between neighbouring sessile drops probed by background-oriented schlieren technique

Despite the extensive progress in the studies of the evaporation of isolated sessile drops for the past decades, little is understood about how they evaporate in a group, which is rather relevant to actual applications such as printing, nanofabrication, cooling and bioassays. While recent theoretical analysis has concerned the evaporation of a pair of thin drops adjacent each other, to the best of our knowledge, no accurate and direct quantitative characterisation of vapour diffusion in such systems has been made, which could assist in a more detailed description of the competitive evaporation. In this contribution, we develop a technique capable of visualising vapour concentration fields around evaporating drops based on the background-oriented schlieren (BOS) principle. Acetone is used in the present study for its sufficient refractive-index contrast of the vapour with air. So far, relative vapour concentration profiles have been obtained and validated. Furthre analysis has been undertaken to investigate the effect of drop size and distance on the evaporative flux distributions.