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Charged systems in, out of, and driven to equilibrium : from nanocapacitors to cement

Abstract : Most systems in soft matter are immersed in solutions with charged species. Some of them can be described by mean-field techniques, while others require more sophisticated treatments that account for correlations between ions.In the first part of this thesis, we analyze the relaxation dynamics of a nanocapacitor. We use analytical and numerical techniques within mean-field (so-called Poisson-Nernst-Planck formalism). We study characteristic relaxation times in the linear and nonlinear regime and characterize the behavior of the system as a function of salt density and applied voltage. Both the parallel plate and the coaxial geometries are examined. The problem of designing a smart time-dependent applied potential, to drive the system from an initial to a final equilibrium state is also tackled, with regard to both the electric double layer build-up process and the establishment of an electroosmotic flow.In the second part, the physics of correlated charged systems is presented, with particular focus on the like-charge attraction phenomenon. We develop a theory describing salt-free systems, at arbitrary value of the electrostatic coupling parameter. Inspired partly by the correlation-hole concept and partly by the Poisson-Boltzmann formalism, the theory satisfies a number of exact requirements and can be easily solved numerically.In the third part, we develop the theory of strong coupling for the nanoscopic constituents of set cement. After introducing the history and the present understanding of the physics behind this omnipresent material, we analyze molecular dynamics simulations of the interface between C-S-H platelets (Calcium Silicate Hydrate). We show that the strong cohesion force observed is ultimately due to a decrease in the dielectric permittivity under confinement, which enhances correlations. We study the statistics of ion hydration and obtain analytically the pressure as a function of inter-platelet distance, in excellent agreement with simulations.
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Ivan Palaia. Charged systems in, out of, and driven to equilibrium : from nanocapacitors to cement. Soft Condensed Matter [cond-mat.soft]. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLS398⟩. ⟨tel-02926717⟩

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