van 't Hoff Laboratory for Physical and Colloid Chemistry, Faculty of Sciences, Utrecht University, P.O. Box 80.056, 3508 TB Utrecht, The Netherlands.
J Phys Chem B. 2009 Aug 27;113(34):11604-13. doi: 10.1021/jp903783b.
In this paper, we present a comprehensive study of the sol-gel transitions and liquid crystal phase transitions in aqueous suspensions of positively charged colloidal gibbsite platelets at pH 4-5 over a wide range of particle concentrations (50-600 g/L) and salt concentrations (10(-4)-10(-1) M NaCl). A detailed sol-gel diagram was established by oscillatory rheological experiments. These demonstrate the presence of kinetically arrested states both at high and at low salt concentrations, enclosing a sol region. Birefringence and iridescence show that in the sol state nematic and hexagonal columnar liquid crystal phases are formed. The gel and liquid crystal structures are studied in further detail using small-angle X-ray scattering (SAXS) and cryo-focused ion beam/scanning electron microscopy (cryo-FIB-SEM). The gel formed at high salt concentration shows signatures of a sponge-like structure and does not display birefringence. In the sol region, by lowering the salt concentration and/or increasing the gibbsite concentration, the nematic phase gradually transforms from the discotic nematic (ND) into the columnar nematic (NC) with much stronger side-to-side interparticle correlations. Subsequently, this NC structure can be either transformed into the hexagonal columnar phase or arrested into a birefringent repulsive gel state with NC structure.
本文对 pH 值为 4-5 的正电荷胶体水合氧化铝片在宽粒径浓度（50-600 g/L）和盐浓度范围（10(-4)-10(-1) M NaCl）下的溶胶-凝胶转变和液晶相转变进行了全面研究。通过振荡流变学实验建立了详细的溶胶-凝胶图。这些实验表明，无论是在低盐浓度还是高盐浓度下，都存在动力学停滞状态，包围着溶胶区域。双折射和虹彩表明，在溶胶状态下形成向列相和六方柱状液晶相。使用小角 X 射线散射（SAXS）和冷冻聚焦离子束/扫描电子显微镜（cryo-FIB-SEM）进一步详细研究了凝胶和液晶结构。在高盐浓度下形成的凝胶显示出海绵状结构的特征，并且不显示双折射。在溶胶区域，通过降低盐浓度和/或增加水合氧化铝浓度，向列相逐渐从盘状向列（ND）转变为柱状向列（NC），颗粒间的侧向相互作用更强。随后，这种 NC 结构可以转变为六方柱状相，或者转变为具有 NC 结构的双折射斥力凝胶态而被固定。
