Mechanistic origin of transient electric birefringence anomaly of clay mineral dispersion
Mechanistic origin of transient electric birefringence anomaly of clay mineral dispersion
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DOI：
10.1021/jp012531v
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发表时间：
2002-05-02
影响因子：
3.3
通讯作者：
Hoffmann, H
中科院分区：
文献类型：
--
作者：
Holzheu, S;Hoffmann, H
瞬态电双折射（TEB）异常是已知的超过40年。尽管有许多实验结果，到目前为止，还没有一个模型描述TEB异常的分子水平。本文将系统地分析吸附、固体或离子浓度等外部参数对异常的影响。在实验中，我们使用了一种特殊的反电荷粘土矿物。与纯粘土矿物相比，这种材料显示出对盐诱导聚集的不敏感性增强的优点。结果表明，没有多粒子过程的迹象。盐的存在和适宜的地表条件是异常存在的必要条件。吸附非离子物质后异常消失的原因是类永久偶极方向从垂直于粘土矿物表面变为平行于粘土矿物表面。提出的解释模型是基于永久类偶极矩源自统计离子波动导致不同数量的凝聚抗衡离子在斯特恩层的粘土盘的两侧。计算值与实验值吻合良好。当反离子的迁移率高时，该机制产生具有主导垂直分量的偶极子。反离子迁移率的降低导致更大的平行分量。
The transient electric birefringence (TEB) anomaly is known for more than 40 years. Despite many experimental results, there is up to now no model describing the TEB anomaly on a molecular level. In this paper, we will present a systematic analysis of the effect of external parameters such as adsorption, solid or ion concentration on the anomaly. For the experiments, we use a special inversed charge clay mineral. This material shows, compared to pure clay minerals, the advantage of enhanced insensitivity to salt-induced aggregation. The results reveal that there is no indication of multiparticle processes. For the existence of the anomaly, both presence of salt and suitable surface conditions are necessary. The disappearance of the anomaly upon adsorption of nonionic substances is due to a change of permanent-like dipole direction from perpendicular to parallel to the clay mineral surface. The explanation model proposed is based on permanent-like dipole moments originating from statistical ion fluctuations leading to different numbers of condensed counterions in the Stern layers of the two sides of the clay disk. Calculated values agree well with experimental quantities. When the mobility of the counterions is high, the mechanism produces a dipole with a dominant perpendicular component. A decrease in counterion mobility leads to a larger parallel component.