title: Temperature dependence of the Soret coefficient of ionic colloids.
abstract: The temperature dependence of the Soret coefficient S(T)(T) in electrostatically charged magnetic colloids is investigated. Two different ferrofluids, with different particles' mean dimensions, are studied. In both cases we obtain a thermophilic behavior of the Soret effect. The temperature dependence of the Soret coefficient is described assuming that the nanoparticles migrate along the ionic thermoelectric field created by the thermal gradient. A model based on the contributions from the thermoelectrophoresis and variation of the double-layer energy, without fitting parameters, is used to describe the experimental results of the colloid with the bigger particles. To do so, independent measurements of the ζ potential, mass diffusion coefficient, and Seebeck coefficient are performed. The agreement of the theory and the experimental results is rather good. In the case of the ferrofluid with smaller particles, it is not possible to get experimentally reliable values of the ζ potential and the model described is used to evaluate this parameter and its temperature dependence.
authors.affiliation: Instituto de Física, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: A L
authors.initials: AL
authors.lastname: Sehnem
authors.affiliation: Instituto de Física, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: A M
authors.initials: AM
authors.lastname: Figueiredo Neto
authors.affiliation: Faculdade UnB-Planaltina, Universidade de Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: R
authors.initials: R
authors.lastname: Aquino
authors.affiliation: Faculdade UnB-Planaltina, Universidade de Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: A F C
authors.initials: AF
authors.lastname: Campos
authors.affiliation: Instituto de Química, Universidade de Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: F A
authors.initials: FA
authors.lastname: Tourinho
authors.affiliation: Instituto de Física, Universidade de Brasília, Brasília, Distrito Federal, Brazil.
authors.forename: J
authors.initials: J
authors.lastname: Depeyrot