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Inversion of thermodiffusive properties of ionic colloidal dispersions in water-DMSO mixtures probed by forced Rayleigh scattering

Abstract : Thermodiffusion properties at room temperature of colloidal dispersions of hydroxyl-coated nanoparticles (NPs) are probed in water, in dimethyl sulfoxide (DMSO) and in mixtures of water and DMSO at various proportions of water, xW . In these polar solvents, the positive NPs superficial charge imparts the systems with a strong electrostatic interparticle repulsion, slightly decreasing from water to DMSO, which is here probed by Small Angle Neutron Scattering and Dynamic Light Scattering. However if submitted to a gradient of temperature, the NPs dispersed in water with ClO4- counterions present a thermophilic behavior, the same NPs dispersed in DMSO with the same counterions present a thermophobic behavior. Mass diffusion coefficient Dm and Ludwig-Soret coefficient ST are measured as a function of NP volume fraction Φ at various xW . The Φ -dependence of ST is analyzed in terms of thermoelectric and thermophoretic contributions as a function of xW . Using two different models for evaluating the Eastman entropy of transfer of the co- and counterions in the mixtures, the single-particle thermophoretic contribution (the NP's Eastman entropy of transfer) is deduced. It is found to evolve from negative in water to positive in DMSO. It is close to zero on a large range of xW values, meaning that in this xW -range ST largely depends on the thermoelectric effect of free co- and counterions.
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Submitted on : Monday, September 2, 2019 - 10:42:11 AM
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M. Sarkar, J. Riedl, G. Demouchy, F. Gélébart, G. Mériguet, et al.. Inversion of thermodiffusive properties of ionic colloidal dispersions in water-DMSO mixtures probed by forced Rayleigh scattering. European Physical Journal E: Soft matter and biological physics, EDP Sciences: EPJ, 2019, 42 (6), pp.72. ⟨10.1140/epje/i2019-11835-6⟩. ⟨hal-02275964⟩

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