Laboratoire Environnement et Minéralurgie, Nancy University, CNRS, UMR 7569, BP40 54501 Vandœuvre Lès Nancy Cedex, France.
J Phys Chem B. 2010 Dec 16;114(49):16347-55. doi: 10.1021/jp105714v. Epub 2010 Nov 22.
The structure of a colloidal dispersion consisting of anisometric natural clay particles (beidellite) was followed under shear-flow conditions by small-angle X-ray scattering (SAXS) measurements in a Couette-type cell. It is shown that in this shear-thinning dispersion an orientational order develops with increasing shear rate. By use of two different geometrical configurations for SAXS measurements, corresponding to incident beam parallel and perpendicular to flow velocity gradient (radial and tangential configurations, respectively), it is observed that SAXS patterns are anisotropic in both geometries, meaning that particles tend to align along a preferred orientation with their normal in velocity gradient direction, and further they partly rotate around flow streamlines. Quantitative interpretation of these results is successfully achieved upon derivation of a probability distribution function accounting for biaxial particle orientation. From this distribution and following geometrical arguments, the viscosity of the suspension was calculated for each shear rate and found to correctly compare with rheological measurements, thereby appropriately relating the anisotropy of the SAXS patterns to macroscopic flow behavior of the suspension.
采用小角 X 射线散射（SAXS）在 Couette 型流变仪中对由各向异性天然膨润土颗粒（贝得石）组成的胶体分散体系在剪切流条件下的结构进行了跟踪研究。结果表明，在这种剪切变稀的分散体系中，随着剪切速率的增加，会出现取向有序。通过对两种不同的 SAXS 测量几何结构（分别对应于平行于和垂直于流速梯度的入射光束（径向和切向配置））的使用，观察到两种几何结构中的 SAXS 图谱均具有各向异性，这意味着颗粒倾向于沿其法向与流速梯度方向对齐的优选方向排列，并且它们进一步围绕流流线部分旋转。通过推导一个考虑双轴颗粒取向的概率分布函数，成功地对这些结果进行了定量解释。从该分布并根据几何论证，计算了每个剪切速率下悬浮液的粘度，并发现与流变学测量结果相符，从而将 SAXS 图谱的各向异性与悬浮液的宏观流动行为适当相关联。
