Sorbonne Université, CNRS, Lab. PHENIX, F-75005, Paris, France.
Phys Chem Chem Phys. 2018 Jun 20;20(24):16402-16413. doi: 10.1039/c8cp02558d.
Thermodiffusion of different ferrite nanoparticles (NPs), ∼10 nm in diameter, is explored in tailor-made aqueous dispersions stabilized by electrostatic interparticle interactions. In the dispersions, electrosteric repulsion is the dominant force, which is tuned by an osmotic-stress technique, i.e. controlling of osmotic pressure Π, pH and ionic strength. It is then possible to map Π and the NPs' osmotic compressibility χ in the dispersion with a Carnahan-Starling formalism of effective hard spheres (larger than the NPs' core). The NPs are here dispersed with two different surface ionic species, either at pH ∼ 2 or 7, leading to a surface charge, either positive or negative. Their Ludwig-Soret ST coefficient together with their mass diffusion Dm coefficient are determined experimentally by forced Rayleigh scattering. All probed NPs display a thermophilic behavior (ST < 0) regardless of the ionic species used to cover the surface. We determine the NPs' Eastman entropy of transfer and the Seebeck (thermoelectric) contribution to the measured Ludwig-Soret coefficient in these ionic dispersions. The NPs' Eastman entropy of transfer ŝNP is interpreted through the electrostatic and hydration contributions of the ionic shell surrounding the NPs.
不同铁氧体纳米粒子（NPs）的热扩散系数（Thermodiffusion）在由静电粒子间相互作用稳定的定制水基分散体中进行了研究。在这些分散体中，静电排斥是主要作用力，可以通过渗透压技术进行调节，即控制渗透压 Π、pH 值和离子强度。然后，可以通过有效硬球（大于 NPs 核）的卡哈纳-斯塔林形式来绘制 Π 和 NPs 渗透压压缩系数 χ 在分散体中的图。这里使用两种不同的表面离子物种分散 NPs，一种在 pH 值约为 2 或 7，导致正或负的表面电荷。它们的路德维希-索雷特 ST 系数以及它们的质量扩散 Dm 系数通过强制瑞利散射实验来确定。所有探测到的 NPs 都表现出嗜热行为（ST < 0），无论用于覆盖表面的离子物种如何。我们在这些离子分散体中确定了 NPs 的伊斯曼传递熵和 Seebeck（热电）对测量的路德维希-索雷特系数的贡献。通过 NPs 周围离子壳的静电和水合贡献来解释 NPs 的伊斯曼传递熵 ŝNP。
