The rheological properties of sepiolite gels in relation to solution chemistry, fiber charge, and microstructure are poorly understood. The purpose of this study was to bring more clarity to this topic by quantifying the effects of solution pH, ionic strength, and adsorbed tetrasodium pyrophosphate (TSPP) additive on rheological properties. The electrical charge on sepiolite fibers was investigated to explain the fiber interaction configuration observed in the microstructure. Fiber interaction forces and dynamics explained the ageing behavior of the gel. Sepiolite gels of only a few percent solids displayed long-time ageing behavior, which was manifested by an increasing yield stress with wait time and continued for weeks. The gel microstructure showed randomly orientated rigid fibers with cross configuration attraction. Each fiber experiences both attractive (van der Waals and heterogeneous charge) and repulsive (electric double layer) forces, and initially a net force. The repulsive force causes these fibers to orientate or move continually to achieve a state of force equilibrium and this process takes a long time. The Leong model describes this ageing behavior. For good fiber separation, high intensity probe sonication of the suspension was required. The yield stress increased with sonication time, solids loading, and temperature. The yield stress was absent at pH > 11 and increased to a maximum value at pH < 8. This maximum was insensitive to pH between 4 to 8, and ionic strength up to 1 M KCl. TSPP reduced this maximum and shifted the zero yield stress region to a lower pH, ~7. The zero yield stress state corresponded to a zeta potential with a minimum magnitude of 30 mV.

中文翻译：

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触变一维海泡石凝胶的表面化学、微观结构和流变学

与溶液化学、纤维电荷和微观结构相关的海泡石凝胶的流变特性知之甚少。本研究的目的是通过量化溶液 pH 值、离子强度和吸附焦磷酸四钠 (TSPP) 添加剂对流变特性的影响，使该主题更加清晰。研究了海泡石纤维上的电荷以解释在微观结构中观察到的纤维相互作用构型。纤维相互作用力和动力学解释了凝胶的老化行为。只有几个固体百分比的海泡石凝胶表现出长期老化行为，这表现为随着等待时间增加屈服应力并持续数周。凝胶微观结构显示随机取向的刚性纤维具有交叉配置吸引力。每根纤维都受到吸引力（范德华力和异质电荷）和排斥力（双电层），最初是净力。排斥力使这些纤维不断定向或移动以达到力平衡状态，这个过程需要很长时间。Leong 模型描述了这种老化行为。为了实现良好的纤维分离，需要对悬浮液进行高强度探头超声处理。屈服应力随着超声处理时间、固体负载和温度而增加。屈服应力在 pH > 11 时不存在，在 pH < 8 时增加到最大值。该最大值对 4 到 8 之间的 pH 值和高达 1 M KCl 的离子强度不敏感。TSPP 降低了这个最大值并将零屈服应力区域转移到较低的 pH 值，~7。