van der Beek D, Petukhov A V, Davidson P, Ferré J, Jamet J P, Wensink H H, Vroege G J, Bras W, Lekkerkerker H N W
Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 Apr;73(4 Pt 1):041402. doi: 10.1103/PhysRevE.73.041402. Epub 2006 Apr 5.
The magnetic-field-induced orientational order in the isotropic phase of colloidal gibbsite [Al(OH)3] platelets is studied by means of optical birefringence and small-angle x-ray scattering (SAXS) techniques. The suspensions display field-induced ordering at moderate field strengths (a few Tesla), which increases with increasing particle concentration. The gibbsite particles align their normals perpendicular to the magnetic field and hence possess a negative anisotropy of their diamagnetic susceptibility Delta(chi). The results can be described following a simple, Onsager-like approach. A simplified model is derived that allows one to obtain the orientational distribution function directly from the scattering data. However, it leads to an underestimate of the diamagnetic susceptibility anisotropy Delta(chi). This accounts for the difference between the Delta(chi) values provided by the two experimental techniques (SAXS and magneto-optics). The order of magnitude Delta(chi) approximately 10(-22) J/T(2) lies in between that of goethite suspensions and that of suspensions of organic particles.
通过光学双折射和小角X射线散射（SAXS）技术研究了胶体三水铝石[Al(OH)₃]薄片各向同性相中的磁场诱导取向有序性。悬浮液在中等场强（几特斯拉）下显示出场诱导有序性，且随着颗粒浓度的增加而增强。三水铝石颗粒将其法线排列成垂直于磁场，因此具有负的抗磁磁化率各向异性Δχ。结果可以按照一种简单的、类似昂萨格的方法来描述。推导了一个简化模型，该模型允许直接从散射数据中获得取向分布函数。然而，它导致了抗磁磁化率各向异性Δχ的低估。这解释了两种实验技术（SAXS和磁光）所提供的Δχ值之间的差异。Δχ的数量级约为10⁻²² J/T²，介于针铁矿悬浮液和有机颗粒悬浮液之间。
