Spatial reorganization of analytes in charged aqueous microdroplets

Spontaneous α-C-H Carboxylation of Ketones by Gaseous CO2 at the Air-water Interface of Aqueous Microdroplets

We present a catalyst-free route for the reduction of carbon dioxide integrated with the formation of a carbon-carbon bond at the air/water interface of negatively charged aqueous microdroplets, at ambient temperature. The reactions proceed through carbanion generation at the α-carbon of a ketone followed by nucleophilic addition to CO2. Online mass spectrometry reveals that the product is an α-ketoacid. Several factors, such as the concentration of the reagents, pressure of CO2 gas, and distance traveled by the droplets, control the kinetics of the reaction. Theoretical calculations suggest that water in the microdroplets facilitates this unusual chemistry. Furthermore, such a microdroplet strategy has been extended to seven different ketones. This work demonstrates a green pathway for the reduction of CO2 to useful carboxylated organic products.

Spontaneous weathering of natural minerals in charged water microdroplets forms nanomaterials

In this work, we show that particles of common minerals break down spontaneously to form nanoparticles in charged water microdroplets within milliseconds. We transformed micron-sized natural minerals like quartz and ruby into 5- to 10-nanometer particles when integrated into aqueous microdroplets generated via electrospray. We deposited the droplets on a substrate, which allowed nanoparticle characterization. We determined through simulations that quartz undergoes proton-induced slip, especially when reduced in size and exposed to an electric field. This leads to particle scission and the formation of silicate fragments, which we confirmed with mass spectrometry. This rapid weathering process may be important for soil formation, given the prevalence of charged aerosols in the atmosphere.

Electro-optics of confined systems

Confinement in microenvironments occurs in many natural systems and technological applications. However, little is known about the behaviour of the immersed nanoparticles. In this work we show that their diffusion, electro-orientation and electric field induced polarization can be determined through electric birefringence experiments. We analyze aqueous dispersions of silver nanowires and clay particles confined inside microdroplets. We have observed that confinement reduces the amount of particles that can be oriented by the external electric field. However, the polarizability of the oriented particles is not affected by the presence of the oil/water boundary, and it is the same as in unbounded media, which agrees with the fact that the electric polarization and related phenomena are short-ranged.

Detecting Early-Stage Intermediates of Free-Radical Oxidative Degradation in Charged Aqueous Microdroplets

We report the detection of early-stage intermediates of spontaneous free-radical oxidation of organic pollutants such as aliphatic amino alcohols and diamines in charged aqueous microdroplets in the ambient atmosphere. We propose that the intrinsic formation of reactive oxygen species at the air-water interface is responsible for the radical oxidation of the sp3 carbon. We suggest that our work will aid the understanding of the degradation mechanisms of organic molecules in the environment.

Aggregation of molecules is controlled in microdroplets

Fluorescence microscopy reveals the control of aggregation and de-aggregation of molecules in microdroplets, which is strikingly different from that in the bulk.