Bimolecular charge transfer reactions at and through the liquid-liquid interface

Interfaces are ubiquitous in Nature. Among them, soft interfaces are essential constituents of biological tissues. Indeed, many electrochemical reactions and phenomena take place at these interfaces. In this respect, ITIES are an interesting model to study such phenomena because they are notably easier to experimentally setup. Nevertheless, some theoretical aspects governing their behaviour are still to be clarified before they can be possibly transposed to biological systems. Thus, the present thesis aims at bringing the progress accomplished in the domains of Time-Resolved Second Harmonic Generation (TRSHG) and molecular mechanics simulations to the study of ITIES First, we present a molecular mechanics study of the structure of the polarised soft interfaces. It is shown that, contrary to the predictions of classical Goüy-Chapman type models, ITIES are devoid of diffuse layers and that the main part of the potential drop occurs at the interface, over few nanometres. Based on these results, a qualitative description of the capacitance curves of these interfaces is proposed and shows that they can be essentially seen as a plan capacitor, given that account is taken of the free energy profile of the ions close to the interface. Secondly, based on the conclusions of the first experimental chapter, we revisit the possibility to carry out electron transfer reactions at ITIES. It it shown that such reactions are indeed possible but that the interface structure significantly impact their kinetic. Here, the possibility to directly control an intermolecular electron transfer is discussed and proposed as a novel way to realise chemical reactions. Finally, the last chapter presents an original study of a diffusion- controlled bimolecular reaction between molecules adsorbed in the plan of the interface. Interestingly, the kinetic of this reaction is influenced by the concentration dependent diffusion regime. Thus, at low surface coverage, the kinetic can be described within the Shmoluchowski model transposed to two-dimensional systems. Nevertheless, with the increase of surface coverage, the diffusion becomes "anomalous" and can no longer be described with a classical approach. The progressive change of diffusion regime is also observed in molecular mechanics simulations realised on similar time-scales. Thus, we think that this thesis presents interesting results that shed light on some aspects of electrochemistry at the ITIES. Also, it should be a useful basis for further studies of these interfaces and, eventually, of biological interfaces.

Girault, Hubert
Olaya Avendano, Astrid Johana
Lausanne, EPFL

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 Record created 2019-11-11, last modified 2020-04-20

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