Aqueous microdroplets: Enhanced reactivity, structure and chemical gradients

Aqueous microdroplets have shown enhanced reactivity wherein the rates of chemical reactions are more than several orders of magnitude higher than compared to the bulk phase. The “unique environment” of the microdroplet, especially at the interface, such as the enrichment of species at the air/water interface, interfacial charge and pH, as well as chemical gradients of different species, has been suggested as the origin of these enhanced rates. Although there exists a great deal of experimental data to support these observations, there still remains a dearth of knowledge of the in-situ reaction kinetics, mechanisms and critical physicochemical properties of microdroplets that make them distinct environments that provide a pathway to overcome typical thermodynamic and kinetic limitations for reactions in the aqueous phase. Using the micro-Raman spectrometer and aerosol optical tweezers, we in situ measure the reactivity of individual aqueous microdroplets in an RH- and temperature-controlled environmental cell. We characterize the properties of air-water interface by Langmuir trough, surface tension measurements and IR-reflection absorption spectroscopy. We are working on sulfate formation, aldol condensation and ester hydrolysis reactions.