Interfacial electromigration for accelerated reactions.

Background: Microdroplets have emerged as effective confined-volume reactors due to their remarkable ability to accelerate chemical reactions compared to bulk systems. Recent research highlights the crucial role of air-liquid interfaces in this acceleration. A microdroplet can be viewed as having two kinetically distinct regions: the interface and the interior. Although the surface area represents a small portion of the total droplet, the overall reaction acceleration hinges on efficient diffusion, ensuring that a substantial proportion of reagents reach the interface for rapid surface reactions. In larger droplets, however, the rate of acceleration can be hindered by slower diffusion.

Results: In this study, we present a novel method that employs electromigration to deliver reactants directly to the surface of a chemical solution contained within an 80 μm diameter theta capillary. This approach, termed as the large orifice theta interfacial microreactor, enhances reaction rates by overcoming diffusion limitations and ensuring immediate acceleration at the air-liquid interface. We applied this approach to accelerated Pd electrocatalysis, electro-oxidative C-H/N-H coupling, and multi-level lipid derivatization. Moreover, by controlling thin film electromigration, we can selectively control product formation in competing reactions, the ability to selectively control product formation in competing reactions, such as the electro-oxidative C-H/N-H coupling of phenothiazine (PTZ) and N,N'-dimethylaniline (DMA), v.s. the dimerization of DMA, and lipid epoxidation v.s. Mn adduction, a feature unattainable in traditional single-barrel or bulk reactions.

Significance: This work introduces a novel platform for accelerating chemical reactions at microdroplet interfaces. The large orifice theta interfacial microreactor not only improves reaction rates by overcoming diffusion barriers but also allows for selective product formation in multi-reaction systems. This method opens new avenues for studying and harnessing the unique properties of microdroplet interfaces for accelerated chemical reactions. Its potential for enhancing reaction selectivity and efficiency marks a significant advancement in the field of microdroplet chemistry.