LEAPS-MPS: Quantifying Interfacial Molecular Transport and pH in a Single Aqueous Electrospray Droplet

In this project funded by the Mathematical and Physical Sciences Directorate Launching Early-Career Academic Pathways (MPS-LEAPS) Program and managed by the Broadening Participation (CHE-BP) Program in the Division of Chemistry, Professor Michael Jacobs and his students at Texas State University-San Marcos will perform studies aimed at understanding how surface electrification affects the chemical properties of the air-water interface. Many classes of reactions (from condensation to redox to biomolecular) occur several orders of magnitude faster in charged microdroplets than in beaker-scale solution.

Professor Jacobs’s research will explore if reactions at the air-water interface are responsible for these dramatic reaction rate accelerations by quantifying molecular concentration at the electrified surface and explicitly measuring the factors that control molecular transport to the charged air-water interface. This research will provide a fundamental understanding of how compartmentalization in microdroplets changes chemical reactivity which can inform how microdroplet chemistry could be deployed for practical applications, such as targeted accelerated chemical syntheses.

Furthermore, this project will train a diverse group of students from Texas State University-San Marcos and will lead to the development of in-lecture chemistry demonstration kits that can be used in chemistry courses to encourage students from historically marginalized groups to participate in research.

Professor Jacobs and his students will use a quadrupole electrodynamic trap to probe interfacial molecular transport and pH in levitated, highly-charged, ‘electrospray’ droplets with well-defined size and composition. Dynamic and equilibrium surface tension measurements on individual charged microdroplets will be used to assess how electrostatic interactions from large electric surface potentials (approaching the Rayleigh limit) affect the partitioning of molecules with a variety of chemical compositions to the air-water interface.

Additionally, they will measure how pH-sensitive molecules partition to the surface of electrospray droplets to explore how electrification changes the acidity of the air-water interface. By explicitly measuring both interfacial transport and pH, Professor Jacobs and his students will develop a fundamental description of how confinement in electrospray droplets drives accelerated chemical reactivity.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.