Sol-gel and isotropic/nematic transitions in aqueous suspensions of natural nontronite clay. Influence of particle anisotropy. 2. Gel structure and mechanical properties.
Sol-gel and isotropic/nematic transitions in aqueous suspensions of natural nontronite clay. Influence of particle anisotropy. 2. Gel structure and mechanical properties.
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DOI：
10.1021/la801894a
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发表时间：
2009-01
期刊：
影响因子：
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通讯作者：
L. Michot;C. Baravian;I. Bihannic;Solange Maddi;C. Moyne;J. Duval;P. Levitz;P. Davidson
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文献类型：
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作者：
L. Michot;C. Baravian;I. Bihannic;Solange Maddi;C. Moyne;J. Duval;P. Levitz;P. Davidson
尺寸选择后，通过渗透压测量、流变实验和小角 X 射线散射分析绿脱石粘土水悬浮液的相行为。所有测量都证实，对于离子强度<或=10(-3) M/L，系统是纯粹排斥的。通过结合渗透压测量和 X 射线散射的结果，似乎可以使用基于带电无限平行平面之间的相互作用的简单泊松-玻尔兹曼处理来很好地描述系统的压力。就流变性质而言，即使溶胶/凝胶转变的状态仍然部分不清楚，因为溶胶-凝胶转变时颗粒的数密度与平均颗粒尺寸呈-2次方依赖性，但凝胶的屈服应力和弹性可以根据颗粒的体积轻松地针对所有颗粒尺寸重新归一化。此外，流动曲线的流变模型表明，对于所有颗粒，基于排除体积效应的方法捕获了绿脱石悬浮液的大部分特征。尽管如此，悬浮液的高剪切流动特性揭示了流动中颗粒的强烈取向，受到静电相互作用的影响。这项研究表明，粘土矿物丰富的相行为，特别是一些粘土矿物表现出各向同性/向列相转变，而其他粘土矿物则表现出溶胶-凝胶转变，需要充分了解系统中的所有相互作用，而这只能通过对特征良好的精选尺寸样品进行研究才能实现。
After size-selection, the phase behavior of aqueous suspensions of nontronite clay was analyzed by osmotic pressure measurements, rheological experiments, and small-angle X-ray scattering. All the measurements confirm that for ionic strength < or =10(-3) M/L, the system is purely repulsive. By combining results from osmotic pressure measurements and X-ray scattering, it appears that the pressure of the system can be well-described using a simple Poisson-Boltzmann treatment based on the interaction between charged infinite parallel planes. In terms of rheological properties, even if the status of the sol/gel transition remains partially unclear as the number density of particles at the sol-gel transition exhibits a -2 power dependence with average particle size, the yield stress and elasticity of the gels can be easily renormalized for all particle sizes on the basis of the volume of the particles. Furthermore, rheological modeling of the flow curves shows that for all the particles, an approach based on excluded volume effects captures most features of nontronite suspensions. Still, the high shear flow properties of the suspensions that reveal a strong orientation of particles in the flow are affected by electrostatic interactions. This study then shows that the rich phase behavior of clay minerals, notably the fact that some clay minerals display an isotropic/nematic transition while others exhibit a sol-gel transition, requires a full understanding of all the interactions in the system that can only be achieved by working on well-characterized size-selected samples.