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Controlling self-assembly and buckling in nano fluid droplets through vapour mediated interaction of adjacent droplets

Hegde, Omkar, Kabi, Prasenjit, Agarwal, Shashwat, Basu, Saptarshi
Journal of colloid and interface science 2019 v.541 pp. 348-355
adsorption, bioassays, droplets, ethanol, evaporation, mixing, nanofluids, nanoparticles, remote control, vapors
Sessile droplets of contrasting volatilities can communicate via long range (∼O (1) mm) vapour-mediated interactions which allow the remote control of the flow driven self-assembly of nanoparticles in the drop of lower volatility. This allows morphological control of the buckling instability observed in evaporating nanofluid droplets.A nanofluid droplet is dispensed adjacent to an ethanol droplet. Asymmetrical adsorption induced Marangoni flow (∼O (1) mm/s) internally segregates the particle population. Particle aggregation occurs preferentially on one side of the droplet leaving the other side to develop a relatively weaker shell which buckles under the effect of evaporation driven capillary pressure.The inter-droplet distance is varied to demonstrate the effect on the precipitate shape (flatter to dome shaped) and the location of the buckling (top to side). In addition to being a simple template for hierarchical self-assembly, the presented exposition also promises to enhance mixing rates (∼1000 times) in droplet-based bioassays with minimal contamination.