Experimental Determination of the Soret Coefficient of Ionic Ferrofluids: Influence of the Volume Fraction and Ionic Strength

Abstract

mental determination of the Soret coefficient of ionic ferrofluids Influence of the volume fraction and the ionic strength. Journal of Non-Equilibrium Thermodynamics, De Gruyter, 2007, 32, pp.271-279 In the present work, we determine the Soret coefficient S T and the thermal diffusion coefficient D T of magnetic colloids (ferrofluids). It has been theoretically predicted that the thermal diffusion coefficient D T of colloids depends both on the particle/solvent interfacial interaction and on the interactions between the colloidal particles. In order to understand the microscopic behavior of the Soret effect in these ionic magnetic colloids, experiments are performed on aqueous samples of various volume fractions Φ and ionic strengths. The dominant effect on the Soret coefficient comes here from the particle/solvent interaction and determines its sign. Interparticle interactions have an influence on S T in the moderate concentration range where virial like expansions are possible. In this range (Φ ≤ 0.10) and within the experimental error bar, the thermal diffusion does not depend on the ionic strength of the dispersion and the Φ-dependence of the friction coefficient is comparable to that of hard spheres. At larger concentrations, the thermal diffusion drastically decreases as the colloid approaches its dynamical glass transition.

Repulsive and attractive ferroglasses: a SAXS and XPCS study

“…In the upper part of the diagram, the thermal diffusion coefNanoparticle do (nm) σ γ/Φ A 9.5 0.35 57 B 8.5 0.35 44 ficient, as measured with a Forced Rayleigh Scattering device [18] through the determination of the massic diffusion coefficient and the Soret coefficient, decreases at increasing the volume fraction (see Figure 2). It drastically decreases while approaching a volume fraction Φ * above which the creation of the spatial concentration modulations produced in the experiment by the Soret effect is no longer possible in a reasonable time scale.…”

Estudo da microestrutura de nanocoloides magnéticos por espalhamento de raio-x em baixo ângulo

“…Na literatura são encontrados para amostras citratadas na faixa de fração volumétrica de 5∼10%, compressibilidades em torno de 0,2∼0,4 [70,95] , valores mais próximos dos resultados obtidos pelo ajuste de Hard Sphere. Porém, medidas de termodifusão realizadas por Gomes [42] utilizando amostras ácidas apresentam compressibilidades com valores abaixo de 0,2 para φ acima de 2%, condizente com os ajustes realizados pela abordagem de distorções paracristalinas.…”

Investigação da relação entre coeficientes termodifusivos em colóides magnéticos a base de água

“…Devido ao interesse em explorar as propriedades físicas dos ferrouidos, vários trabalhos já investigaram seu comportamento termodifusivo [17,18,19,20,21,22,23], que é o acúmulo de partículas induzido por um gradiente de temperatura para a parte fria ou quente da solução. Existem duas linhas distintas de pesquisa, considerando ou não a inuência de campo magnético na termodifusão das nanopartículas de óxidos de ferro.…”