Fiuza T, Sarkar M, Riedl J C, Cēbers A, Cousin F, Demouchy G, Depeyrot J, Dubois E, Gélébart F, Mériguet G, Perzynski R, Peyre V
Sorbonne Université, CNRS, Lab. PHENIX, 4 Place Jussieu, F-75005 Paris, France.
MMML Lab, Faculty of Physics and Mathematics, University of Latvia, Zellu-8, LV- 1002 Riga, Latvia.
Soft Matter. 2021 May 5;17(17):4566-4577. doi: 10.1039/d0sm02190c.
Ferrofluids based on maghemite nanoparticles (NPs), typically 10 nm in diameter, are dispersed in an ionic liquid (1-ethyl 3-methylimidazolium bistriflimide - EMIM-TFSI). The average interparticle interaction is found to be repulsive by small angle scattering of X-rays and of neutrons, with a second virial coefficient A2 = 7.3. A moderately concentrated sample at Φ = 5.95 vol% is probed by forced Rayleigh scattering under an applied magnetic field (up to H = 100 kA m-1) from room temperature up to T = 460 K. Irrespective of the values of H and T, the NPs in this study are always found to migrate towards the cold region. The in-field anisotropy of the mass diffusion coefficient Dm and that of the (always positive) Soret coefficient ST are well described by the presented model in the whole range of H and T. The main origin of anisotropy is the spatial inhomogeneities of concentration in the ferrofluid along the direction of the applied field. Since this effect originates from the magnetic dipolar interparticle interaction, the anisotropy of thermodiffusion progressively vanishes when temperature and thermal motion increase.
基于直径通常为10纳米的磁赤铁矿纳米颗粒（NPs）的铁磁流体，分散于离子液体（1-乙基-3-甲基咪唑双三氟甲磺酰亚胺 - EMIM-TFSI）中。通过X射线和中子的小角散射发现，平均粒子间相互作用是排斥性的，第二维里系数A2 = 7.3。在从室温到T = 460 K的温度范围内，在高达H = 100 kA m-1的外加磁场下，通过强迫瑞利散射对浓度为Φ = 5.95 vol%的中等浓度样品进行探测。无论H和T的值如何，本研究中的纳米颗粒总是朝着低温区域迁移。在所呈现的模型中，质量扩散系数Dm和（始终为正的）索雷特系数ST的场内各向异性在整个H和T范围内都得到了很好的描述。各向异性的主要来源是铁磁流体中沿外加磁场方向的浓度空间不均匀性。由于这种效应源于磁偶极粒子间相互作用，当温度和热运动增加时，热扩散的各向异性逐渐消失。
