The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform

Simone Wiegand - One of the best experts on this subject based on the ideXlab platform.

  • Diffusiophoresis as ruling effect: Influence of organic salts on thermodiffusion of iron oxide nanoparticles
    Physical Review E, 2018
    Co-Authors: André Luiz Sehnem, Antônio Martins Figueiredo Neto, Doreen Niether, Simone Wiegand
    Abstract:

    Colloidal particles, including ferrofluidic nanoparticles (NP), move in a temperature gradient due to thermodiffusion. Organic salts, which are often added to disperse the NP in aqueous solution, also move in the temperature gradient. This can have a strong influence on the behavior of the NP, which not only respond to the temperature gradient but also to the concentration gradient of the dispersive salt, an effect termed diffusiophoresis. In this work we present experimental results on thermodiffusion of iron oxide nanoparticles dispersed in aqueous solutions of organic hydroxides, which illustrate the possibility to manipulate the thermodiffusion of NP through the addition of organic salts. Our experiments investigate the temperature dependence of the particles' Soret Coefficient, a recurring question on thermodiffusion of water-dispersed particles. Existing theoretical approaches are compared and we relate the Soret Coefficient of the NP with two main physical parameters ruling particle motion: the NP's electrostatic potential and the Soret Coefficient of the dispersing ions. These parameters are also experimentally determined. At the order of magnitude of the NP's Soret Coefficient good agreement between experiments and theory is achieved by including the experimental data on the Soret Coefficient of the dispersing ions and therefore the NP's displacement due to the ion concentration gradient. Taking into account the temperature dependence of such previously unknown parameters is a relevant step to describe the temperature dependence of the NP's Soret Coefficient.

  • Thermodiffusion, molecular diffusion and Soret Coefficient of binary and ternary mixtures of n-hexane, n-dodecane and toluene.
    The European physical journal. E Soft matter, 2014
    Co-Authors: David Alonso De Mezquia, Estela Lapeira, Zilin Wang, Michael Klein, Simone Wiegand, M. Mounir Bou-ali
    Abstract:

    In this study, the thermodiffusion, molecular diffusion, and Soret Coefficients of 12 binary mixtures composed of toluene, n-hexane and n-dodecane in the whole range of concentrations at atmospheric pressure and temperatures of 298.15 K and 308.15 K have been determined. The experimental measurements have been carried out using the Thermogravitational Column, the Sliding Symmetric Tubes and the Thermal Diffusion Forced Rayleigh Scattering techniques. The results obtained using the different techniques show a maximum deviation of 9% for the thermodiffusion Coefficient, 8% for the molecular diffusion Coefficient and 2% for the Soret Coefficient. For the first time we report a decrease of the thermodiffusion Coefficient with increasing ratio of the thermal expansion Coefficient and viscosity for a binary mixture of an organic ring compound with a short n-alkane. This observation is discussed in terms of interactions between the different components. Additionally, the thermogravitational technique has been used to measure the thermodiffusion Coefficients of four ternary mixtures consisting of toluene, n-hexane and n-dodecane at 298.15 K. In order to complete the study, the values obtained for the molecular diffusion Coefficient in binary mixtures, and the thermodiffusion Coefficient of binary and ternary mixtures have been compared with recently derived correlations.

  • Alkali halide solutions under thermal gradients: Soret Coefficients and heat transfer mechanisms.
    The journal of physical chemistry. B, 2013
    Co-Authors: Frank Römer, Zilin Wang, Simone Wiegand, Fernando Bresme
    Abstract:

    We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na+/K+–Cl–) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret Coefficient. We find the Soret Coefficient is of the order of 10–3 K–1 for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret Coefficient decreases with concentration at high temperatures (higher than T ∼ 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret Coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret Coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism ...

  • Soret Coefficient in nonionic microemulsions: concentration and structure dependence.
    The journal of physical chemistry. B, 2013
    Co-Authors: Philipp Naumann, Nils Becker, Sascha Datta, Thomas Sottmann, Simone Wiegand
    Abstract:

    Here we investigate the thermal diffusion behavior of the nonionic microemulsion water/n-decane/pentaethylene glycol monododecyl ether (C12E5). We study the dependence of the Soret Coefficient on the structure and composition by infrared thermal diffusion Rayleigh scattering. The form and size of the microemulsion structure is characterized by dynamic light scattering and small angle neutron scattering. The system was examined in the one-phase region between the emulsification failure boundary and the near critical boundary, where oil swollen nanostructures stabilized by an amphiphilic surfactant film are dispersed in a continuous water phase. The size and shape of these structures as well as the interfacial properties of microemulsions can be varied by changing temperature and composition, which allows a systematic study of their influence on the thermal diffusion properties. In addition, we analyze the relationship between the Soret Coefficient and the temperature dependence of the interfacial tension a...

  • Soret Coefficient in Nonionic Microemulsions: Concentration and Structure Dependence B
    The Journal of Physical Chemistry, 2013
    Co-Authors: Philipp Naumann, Nils Becker, Sascha Datta, Thomas Sottmann, Simone Wiegand
    Abstract:

    Here we investigate the thermal diffusion behavior of the nonionic microemulsion water/n-decane/pentaethylene glycol monododecyl ether (C₁₂E₅). We study the dependence of the Soret Coefficient on the structure and composition by infrared thermal diffusion Rayleigh scattering. The form and size of the microemulsion structure is characterized by dynamic light scattering and small angle neutron scattering. The system was examined in the one-phase region between the emulsification failure boundary and the near critical boundary, where oil swollen nanostructures stabilized by an amphiphilic surfactant film are dispersed in a continuous water phase. The size and shape of these structures as well as the interfacial properties of microemulsions can be varied by changing temperature and composition, which allows a systematic study of their influence on the thermal diffusion properties. In addition, we analyze the relationship between the Soret Coefficient and the temperature dependence of the interfacial tension as proposed by A. Parola and R. Piazza (Eur. Phys. J. E2004, 15, 255–263) and find reasonable agreement for spherical microemulsion droplets.

Rio Kita - One of the best experts on this subject based on the ideXlab platform.

  • Temperature dependence of Soret Coefficient in aqueous and nonaqueous solutions of pullulan.
    Biomacromolecules, 2010
    Co-Authors: Yuki Kishikawa, Simone Wiegand, Rio Kita
    Abstract:

    We present experimental results of the temperature dependence of the Ludwig-Soret effect for pullulan solutions. The Soret Coefficients of 5.0 g L(-1) pullulan in water and in dimethyl sulfoxide (DMSO) were determined in the experimental temperature range between 20.0 and 50.0 degrees C by means of thermal diffusion Forced Rayleigh scattering (TDFRS). The sign of the Soret Coefficient of pullulan in water is negative at room temperature, which indicates that the pullulan molecules migrate to the warm side of the fluid. The Soret Coefficient of pullulan increases steeply with increase of the solution temperature and shows a sign change from negative to positive at 41.7 degrees C. The positive sign of the Soret Coefficient means the pullulan molecules move to the cold side. In contrast to the aqueous solution, the solution of pullulan in DMSO shows a very weak temperature dependence of the Soret Coefficient and has always a positive sign. In addition to the TDFRS experiments, we also performed light scattering (LS) experiments for the pullulan solutions under homogeneous temperature condition in a temperature range between 20.0 and 55.0 degrees C. The thermodynamic properties of pullulan solutions obtained by LS show no pronounced correlation with the thermal diffusion behavior of pullulan. These results indicate the existence of a special role of interactions due to solvation on the temperature dependence of the thermal diffusion behavior of polysaccharide solutions.

  • Universal Concentration Dependence of the Soret Coefficient in Aqueous Systems
    Journal of Non-Equilibrium Thermodynamics, 2007
    Co-Authors: Simone Wiegand, Hui Ning, Rio Kita
    Abstract:

    We present measurements of aqueous low molecular weight mixtures and aqueous macromolecular solutions. The Soret Coefficient S-T for ethanol, acetone, and DMSO in water was measured by an optical grating technique, and all systems showed a sign change around a molar fraction of water X-water 0.85 +/- 0.05. ST for poly(ethylene oxide), poly(N-isopropylacrylamide), and boehmite rods in ethanol/water mixtures showed also a sign change close to the same concentration. The occurring sign change concentration in the systems will be related to structural reorganizations in the solvent mixture and the Hildebrandt solubility parameter. We will also compare the experimental data within lattice calculations and simulations, which indicate that strong cross-interactions are important for a sign change of the Soret Coefficient

  • Thermally induced sign change of Soret Coefficient for dilute and semidilute solutions of poly(N-isopropylacrylamide) in ethanol.
    The Journal of chemical physics, 2004
    Co-Authors: Rio Kita, Gunnar Kircher, Simone Wiegand
    Abstract:

    We studied the thermal diffusion behavior of poly(N-isopropylacrylamide) (PNiPAM) in ethanol in a temperature range from T=14.0 °C to T=40.0 °C by means of thermal diffusion forced Rayleigh scattering. The obtained Soret Coefficient ST of PNiPAM was positive for lower temperatures (T 34 °C). This means PNiPAM molecules move to the cold side for temperatures T 34 °C. This is the first nonaqueous polymeric system for which a sign change with temperature has been observed. We performed static and dynamic light scattering experiments in the same temperature range. The second virial Coefficient determined from dilute solutions by static light scattering (SLS) was positive in the comparable temperature range. The results of SLS for the semidilute solution showed a strong repulsion among PNiPAM chains which was enhanced by increasing temperature. These results imply that the observed thermally indu...

  • Sign change of the Soret Coefficient of poly(ethylene oxide) in water/ethanol mixtures observed by thermal diffusion forced Rayleigh scattering
    The Journal of chemical physics, 2004
    Co-Authors: Rio Kita, Simone Wiegand, Jutta Luettmer-strathmann
    Abstract:

    Soret Coefficients of the ternary system of poly(ethylene oxide) in mixed water/ethanol solvent were measured over a wide solvent composition range by means of thermal diffusion forced Rayleigh scattering. The Soret Coefficient ST of the polymer was found to change sign as the water content of the solvent increases with the sign change taking place at a water mass fraction of 0.83 at a temperature of 22 °C. For high water concentrations, the value of ST of poly(ethylene oxide) is positive, i.e., the polymer migrates to the cooler regions of the fluid, as is typical for polymers in good solvents. For low water content, on the other hand, the Soret Coefficient of the polymer is negative, i.e., the polymer migrates to the warmer regions of the fluid. Measurements for two different polymer concentrations showed a larger magnitude of the Soret Coefficient for the smaller polymer concentration. The temperature dependence of the Soret Coefficient was investigated for water-rich polymer solutions and revealed a s...

  • sign change of the Soret Coefficient of poly ethylene oxide in water ethanol mixtures observed by thermal diffusion forced rayleigh scattering
    Journal of Chemical Physics, 2004
    Co-Authors: Rio Kita, Simone Wiegand, Jutta Luettmerstrathmann
    Abstract:

    Soret Coefficients of the ternary system of poly(ethylene oxide) in mixed water/ethanol solvent were measured over a wide solvent composition range by means of thermal diffusion forced Rayleigh scattering. The Soret Coefficient ST of the polymer was found to change sign as the water content of the solvent increases with the sign change taking place at a water mass fraction of 0.83 at a temperature of 22 °C. For high water concentrations, the value of ST of poly(ethylene oxide) is positive, i.e., the polymer migrates to the cooler regions of the fluid, as is typical for polymers in good solvents. For low water content, on the other hand, the Soret Coefficient of the polymer is negative, i.e., the polymer migrates to the warmer regions of the fluid. Measurements for two different polymer concentrations showed a larger magnitude of the Soret Coefficient for the smaller polymer concentration. The temperature dependence of the Soret Coefficient was investigated for water-rich polymer solutions and revealed a s...

Fernando Bresme - One of the best experts on this subject based on the ideXlab platform.

  • The role of ion-water interactions in determining the Soret Coefficient of LiCl aqueous solutions
    Physical chemistry chemical physics : PCCP, 2017
    Co-Authors: Silvia Di Lecce, Tim Albrecht, Fernando Bresme
    Abstract:

    The application of a thermal gradient to an aqueous electrolyte solution induces the Soret effect, and the salt migrates towards hot (thermophilic) or cold regions (thermophobic). Experimental studies of LiCl reported changes in the sign of the Soret Coefficient as well as a minimum in this Coefficient at specific salt concentrations and temperatures. At the minimum the thermodiffusive response of the solution is enhanced significantly. We have performed non-equilibrium molecular dynamics simulations of LiCl solutions to quantify the dependence of the sign change and minimum of the Soret Coefficient with salt concentration and temperature. We find that the ion mass plays a secondary role in determining the magnitude of the Soret Coefficient, while the diameter of the cation has a significant impact on the Coefficient and on the observation of the minimum. Our simulations show that the ordering of water around Li+ plays a key role in determining the Soret Coefficient of LiCl salts.

  • Alkali halide solutions under thermal gradients: Soret Coefficients and heat transfer mechanisms.
    The journal of physical chemistry. B, 2013
    Co-Authors: Frank Römer, Zilin Wang, Simone Wiegand, Fernando Bresme
    Abstract:

    We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na+/K+–Cl–) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret Coefficient. We find the Soret Coefficient is of the order of 10–3 K–1 for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret Coefficient decreases with concentration at high temperatures (higher than T ∼ 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret Coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret Coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism ...

  • Alkali Halide Solutions under Thermal Gradients: Soret Coefficients and Heat Transfer Mechanisms B
    The Journal of Physical Chemistry, 2013
    Co-Authors: Frank Römer, Zilin Wang, Simone Wiegand, Fernando Bresme
    Abstract:

    We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na⁺/K⁺–Cl–) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret Coefficient. We find the Soret Coefficient is of the order of 10–³ K–¹ for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret Coefficient decreases with concentration at high temperatures (higher than T ∼ 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret Coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret Coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism and the behavior of the Soret Coefficient in aqueous solutions. The models employed in this work reproduce the magnitude of the Soret Coefficient, and the general dependence of this Coefficient with temperature and salt concentration. We use the computer simulations as a microscopic approach to establish a correlation between the sign and magnitude of the Soret Coefficients and ionic solvation and hydrogen bond structure of the solutions. Finally, we report an analysis of heat transport in ionic solution by quantifying the solution thermal conductivity as a function of concentration. The simulations accurately reproduce the decrease of the thermal conductivity with increasing salt concentration that is observed in experiments. An explanation of this behavior is provided.

M Kouyate - One of the best experts on this subject based on the ideXlab platform.

  • thermodiffusion of citrate coated γ fe2o3 nanoparticles in aqueous dispersions with tuned counter ions anisotropy of the Soret Coefficient under a magnetic field
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: M Kouyate, Guillaume Mériguet, C L Filomeno, G Demouchy, S Nakamae, Veronique Peyre, Michel Roger, A Cēbers, J Depeyrot
    Abstract:

    Under a temperature gradient, the direction of thermodiffusion of charged γ-Fe2O3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either a positive or negative Soret Coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret Coefficient ST is measured in stationary conditions together with the mass-diffusion Coefficient Dm using a forced Rayleigh scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of Dm with NP volume fraction Φ. The Φ-dependence of ST is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transfer ŜNP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively, with ST > 0 and with ST < 0 are then probed under an applied field , and an anisotropy of Dm and of ST is induced while the in-field system remains monophasic. Whatever the -direction (parallel or perpendicular to the gradients and ), the Soret Coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.

  • Thermodiffusion of citrate-coated γ-Fe2O3 nanoparticles in aqueous dispersions with tuned counter-ions – anisotropy of the Soret Coefficient under a magnetic field
    Physical chemistry chemical physics : PCCP, 2019
    Co-Authors: M Kouyate, Jérôme Depeyrot, Guillaume Mériguet, C L Filomeno, G Demouchy, S Nakamae, Veronique Peyre, Michel Roger, A Cēbers, Emmanuelle Dubois
    Abstract:

    Under a temperature gradient, the direction of thermodiffusion of charged γ-Fe2O3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either a positive or negative Soret Coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret Coefficient ST is measured in stationary conditions together with the mass-diffusion Coefficient Dm using a forced Rayleigh scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of Dm with NP volume fraction Φ. The Φ-dependence of ST is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transfer ŜNP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively, with ST > 0 and with ST < 0 are then probed under an applied field , and an anisotropy of Dm and of ST is induced while the in-field system remains monophasic. Whatever the -direction (parallel or perpendicular to the gradients and ), the Soret Coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.

  • Thermodiffusion of citrate-coated γ-Fe 2 O 3 nanoparticles in aqueous dispersions with tuned counter-ions – anisotropy of the Soret Coefficient under a magnetic field
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: M Kouyate, C L Filomeno, G Demouchy, S Nakamae, Veronique Peyre, Michel Roger, A Cēbers, J Depeyrot, G. Mériguet, E. Dubois
    Abstract:

    Under a temperature gradient, the direction of thermodiffusion of charged g Fe 2 O 3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either positive or negative Soret Coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret Coefficient S T is measured in stationary conditions together with the mass-diffusion Coefficient D m using a Forced Rayleigh Scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of D m with NP's volume fraction F. The F-dependence of S T is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transferŜ NP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively with S T > 0 and with S T < 0 are then probed under an applied fieldH, an anisotropy of D m and of S T is induced while the in-field system remains monophasic. Whatever theH-direction (parallel or perpendicular to the gradients-T and-F), the Soret Coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.

C L Filomeno - One of the best experts on this subject based on the ideXlab platform.

  • thermodiffusion of citrate coated γ fe2o3 nanoparticles in aqueous dispersions with tuned counter ions anisotropy of the Soret Coefficient under a magnetic field
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: M Kouyate, Guillaume Mériguet, C L Filomeno, G Demouchy, S Nakamae, Veronique Peyre, Michel Roger, A Cēbers, J Depeyrot
    Abstract:

    Under a temperature gradient, the direction of thermodiffusion of charged γ-Fe2O3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either a positive or negative Soret Coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret Coefficient ST is measured in stationary conditions together with the mass-diffusion Coefficient Dm using a forced Rayleigh scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of Dm with NP volume fraction Φ. The Φ-dependence of ST is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transfer ŜNP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively, with ST > 0 and with ST < 0 are then probed under an applied field , and an anisotropy of Dm and of ST is induced while the in-field system remains monophasic. Whatever the -direction (parallel or perpendicular to the gradients and ), the Soret Coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.

  • Thermodiffusion of citrate-coated γ-Fe2O3 nanoparticles in aqueous dispersions with tuned counter-ions – anisotropy of the Soret Coefficient under a magnetic field
    Physical chemistry chemical physics : PCCP, 2019
    Co-Authors: M Kouyate, Jérôme Depeyrot, Guillaume Mériguet, C L Filomeno, G Demouchy, S Nakamae, Veronique Peyre, Michel Roger, A Cēbers, Emmanuelle Dubois
    Abstract:

    Under a temperature gradient, the direction of thermodiffusion of charged γ-Fe2O3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either a positive or negative Soret Coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret Coefficient ST is measured in stationary conditions together with the mass-diffusion Coefficient Dm using a forced Rayleigh scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of Dm with NP volume fraction Φ. The Φ-dependence of ST is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transfer ŜNP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively, with ST > 0 and with ST < 0 are then probed under an applied field , and an anisotropy of Dm and of ST is induced while the in-field system remains monophasic. Whatever the -direction (parallel or perpendicular to the gradients and ), the Soret Coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.

  • Thermodiffusion of citrate-coated γ-Fe 2 O 3 nanoparticles in aqueous dispersions with tuned counter-ions – anisotropy of the Soret Coefficient under a magnetic field
    Physical Chemistry Chemical Physics, 2019
    Co-Authors: M Kouyate, C L Filomeno, G Demouchy, S Nakamae, Veronique Peyre, Michel Roger, A Cēbers, J Depeyrot, G. Mériguet, E. Dubois
    Abstract:

    Under a temperature gradient, the direction of thermodiffusion of charged g Fe 2 O 3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either positive or negative Soret Coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret Coefficient S T is measured in stationary conditions together with the mass-diffusion Coefficient D m using a Forced Rayleigh Scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of D m with NP's volume fraction F. The F-dependence of S T is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transferŜ NP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively with S T > 0 and with S T < 0 are then probed under an applied fieldH, an anisotropy of D m and of S T is induced while the in-field system remains monophasic. Whatever theH-direction (parallel or perpendicular to the gradients-T and-F), the Soret Coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.