Dynamic Electrogenerated Chemiluminescence Imaging of Coalescence Phenomenon Uncovers Generation of Multiphase Confined Environments in Sessile Water Droplets

Description:
It has been recently demonstrated that water microdroplets suspended in in 1,2-dichloroethane solution and colliding with the surface of a glassy carbon working electrode entrap volumes of the organic continuous phase.1 This phenomenon manifests the overestimation of the available contact area between the electrode surface and water phase. In this work, we take a step further by analyzing the causes of the organic solvent entrapment. Water microdroplets were loaded with an electrochemiluminescent-active luminophore, 10 mM tris(bipyridine)ruthenium(II) dichloride and 50 mM sodium oxalate. Then, by the application of a oxidative potential, their evolution on the electrode surface was tracked by electrochemiluminescence (ECL) microscopy. The surface-confinement characteristic of this peculiar chemiluminescence event, limited at a maximum of few micrometers from the electrode surface and occurring exclusively in the water phase, drastically increased the resolution at the interface waterǀelectrode. We found that a spontaneous generation of multiple emulsions occurs during the coalescence of two or more water droplets adsorbed on the electrode. A complex multiphasic system, composed by areas of entrapped organic phase and areas of entrapped water phase, results as confined environments inside the water microdroplets. The increase of the interfaces provokes a confinement of the volumes inside the water droplet. The study of the exceptional chemical reactivity in those extremely confined environments is the subject of the ongoing research in our group. Insights in these multiphasic systems will enable to increase our knowledge on subcellular reactivity and on the origin of life. In addition, interesting applications as microreactors in microfluidic device can be developed based on our observations.

1.Glasscott M.W., Voci S., Kauffmann P.J., Chaporal A.J., Dick J.E., Langmuir, 2021, 37, 2907-2912.

Speaker: Silvia Voci - Purdue University