Interfacial and Droplet Reactivity: Mechanisms, Measurement, and Applications

In our five-day program we have organized sessions to begin with the explosive growth of evidence for reaction acceleration in droplets. There is currently a matter of under-reporting experimental conditions that tie to acceleration, and the chosen speakers will engage in what fundamental features of droplets (size, preparation technique, charge etc.) matter and which do not, as well as the exciting potential for how such synthetic abilities and catalysis can scale. But why do droplets accelerate reactions and what mechanistic features can unify the droplet reactivity? One obvious distinguishing feature of droplets relative to bulk is of course their interface, and a second perhaps underappreciated distinction is their ability to hold excess charge and not simply increase bulk solution ionic strength. The designated speakers and discussion leaders were chosen for introducing new and sophisticated interfacial spectroscopies, with theory weighing in on their interpretation, and the need to consider charge and perturbations such as pH. Investigation of the fundamental origins of reactivity, such as the influence of strong electric fields that can make or break chemical bonds or induce redox reactions, is a much-needed discussion that underlies the mechanistic question for rate acceleration. While parts of the program focus mostly on the air-water droplet interface other hydrophobic-water interfaces also accelerate reactions such as oil-water emulsions. There are age-old questions about emulsion stability that have brought on new experiments and theory, and biocondensates bear analogies worth discussing. Special properties of droplet reactivity has opened up avenues for driving chemistry using droplets, for problems of interest in synthesis, energy, and environmental chemistry. Finally, a fruitful dialogue between physical chemists, organic and synthetic chemists, atmospheric scientists and theorists will identify critical questions that can be addressed by a combination of approaches to gain a much-needed molecular understanding of interfacial reactivity.