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Accueil > Séminaires > Année 2022 > Séminaire de Richard Zare en VISIOCONFERENCE (8 avril)

Séminaire de Richard Zare en VISIOCONFERENCE (8 avril)

Department of Chemistry, Stanford University

par Martrenchard-Barra Séverine - 12 mars (modifié le 5 avril)

Les personnes extérieures à l’ISMO qui souhaitent assister à la visioconférence sont invitées à demander le lien à l’adresse mail :
seminaires.ismo@universite-paris-saclay.fr
AVANT le 8 avril, 11h

Can Water Microdroplets Act as Electrochemical Cells ?

Microdroplets are often regarded as useful miniature containers that are analogous to larger-scale bulk reactions. This view is not always valid, particularly, for very small microdroplets wherein the radius starts to approach the Debye length of the electric double layer (EDL). Microdroplets end up with a charged surface, and in the case of water microdroplets experiments show that the surface is negatively charged. The exact charging mechanism is a matter of debate ; here we assume either a deliberately added charged surfactant or localization of trace contaminants and hydroxide ions (OH-) at the surface. As a result, an EDL forms inside the droplet. Depletion of ions from the center of the droplet to form the EDL can shift the concentration of ions dramatically from that of the microdroplet precursor solution and forms a hydrogen ion (H+) gradient within the microdroplet. We present a treatment of micron-sized water microdroplets using a simple continuum model that includes the ability to handle weak electrolytes that would typically buffer any H+ gradient as well as handle the autoionization of water within the microdroplet. The radial ion gradient and the electric field inside the droplet cause the net reaction rate to be dramatically different from the reaction rate of the average reagent concentrations via several different effects which we examine. Furthermore, we consider the possibility of the surface charge being discharged into the interior of the droplet via a redox reaction with surfactant ions. We define and then calculate the effective voltage supplied by the EDL of the microdroplet for this unusual type of redox chemistry. Several experiments are presented showing the redox power of water microdroplets.