Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandoeuvre Cedex France.
J Phys Chem B. 2009 Dec 3;113(48):15858-69. doi: 10.1021/jp908326y.
After size-selection and osmotic pressure measurements at fixed ionic strength, the behavior of aqueous colloidal suspensions of anisotropic disklike beidellite clay particles has been investigated by combining optical observations under polarized light, rheological, and small angle X-ray scattering (SAXS) experiments. The obtained phase diagrams (volume fraction/ionic strength) reveal, for ionic strength below 10(-3) M/L, a first-order isotropic/nematic (I/N) phase transition before gel formation at low volume fractions, typically around 0.5%. This I/N transition line displays a positive slope for increasing ionic strength and shifts toward lower volume fraction with increasing particle size, confirming that the system is controlled by repulsive interactions. The swelling laws, derived from the interparticle distances obtained by SAXS, display a transition from isotropic swelling at low volume fractions to lamellar swelling at higher volume fractions. The liquid-crystal properties have then been investigated in detail. Highly aligned nematic samples can be obtained in three different ways, by applying a magnetic field, an ac electric field, and by spontaneous homeotropic anchoring on surfaces. The birefringence of the fluid nematic phase is negative with typical values around 5 x 10(-4) at a volume fraction of about 0.6%. High nematic order parameters have been obtained as expected for well-aligned samples. The nematic director is aligned parallel to the magnetic field and perpendicular to the electric field.
在固定离子强度下进行尺寸选择和渗透压测量后，通过结合偏光下的光学观察、流变学和小角 X 射线散射（SAXS）实验，研究了各向异性盘状贝得石粘土颗粒的水胶体悬浮液的行为。获得的相图（体积分数/离子强度）表明，在离子强度低于 10(-3) M/L 时，在低体积分数下（通常约为 0.5%）发生了第一类各向同性/向列（I/N）相转变，然后形成凝胶。该 I/N 转变线在离子强度增加时呈正斜率，并且随着粒径的增加向低体积分数移动，这证实了该体系由排斥相互作用控制。通过 SAXS 获得的颗粒间距离推导出的溶胀规律显示，在低体积分数下从各向同性溶胀转变为高体积分数下的层状溶胀。然后详细研究了液晶性质。可以通过施加磁场、交流电场和在表面自发形成向列锚定这三种不同的方法获得高度取向的向列样品。在体积分数约为 0.6%时，流体向列相的双折射为负，典型值约为 5 x 10(-4)。由于样品取向良好，获得了高向列序参数。向列指向平行于磁场且垂直于电场。
