Marín-Santibañez Benjamín M, Pérez-Gonzalez José, de Vargas Lourdes, Rodríguez-Gonzalez Francisco, Huelsz Guadalupe
Laboratorio de Reología, Escuela Superior de Física y Matematicas, Instituto Politécnico Nacional, Apdo. Postal 118-209, C. P. 07051, México D. F. México.
Langmuir. 2006 Apr 25;22(9):4015-26. doi: 10.1021/la053167k.
The shear-thickening behavior of an equimolar semidilute aqueous solution of 40 mM/L cetylpyridinium chloride and sodium salicylate was studied in this work by using a combined method of rheometry and particle image velocimetry (PIV). Experiments were conducted at 27.5 degrees C with Couette, vane-bob, and capillary rheometers in order to explore a wide shear stress range as well as the effect of boundary conditions and time of flow on the creation and destruction of shear-induced structures (SIS). The use of the combined method of capillary rheometry with PIV allowed the detection of fast spatial and temporal variations in the flow kinematics, which are related to the shear-thickening behavior and the dynamics of the SIS but are not distinguished by pure rheometrical measurements. A rich-in-details flow curve was found for this solution, which includes five different regimes. Namely, at very low shear rates a Newtonian behavior was found, followed by a shear thinning one in the second regime. In the third, shear banding was observed, which served as a precursor of the SIS and shear-thickening. The fourth and fifth regimes in the flow curve were separated by a spurtlike behavior, and they clearly evidenced the existence of shear-thickening accompanied by stick-slip oscillations at the wall of the rheometer, which subsequently produced variations in the shear rate under shear stress controlled flow. Such a stick-slip phenomenon prevailed up to the highest shear stresses used in this work and was reflected in asymmetric velocity profiles with spatial and temporal variations linked to the dynamics of creation and breakage of the SIS. The presence of apparent slip at the wall of the rheometer provides an energy release mechanism which leads to breakage of the SIS, followed by their further reformation during the stick part of the cycles. In addition, PIV measurements allowed the detection of apparent slip at the wall, as well as mechanical failures in the bulk of the fluid, which suggests an extra contribution of the shear stress field to the SIS dynamics. Increasing the residence time of the fluid in the flow system enhanced the shear-thickening behavior. Finally, the flow kinematics is described in detail and the true flow curve is obtained, which only partially fits into the scheme of existing theoretical models for shear-thickening solutions.
本研究采用流变学和粒子图像测速技术（PIV）相结合的方法，对40 mM/L十六烷基吡啶氯化物和水杨酸钠的等摩尔半稀水溶液的剪切增稠行为进行了研究。实验在27.5℃下使用库埃特流变仪、叶片-柱体流变仪和毛细管流变仪进行，以探索较宽的剪切应力范围以及边界条件和流动时间对剪切诱导结构（SIS）的形成和破坏的影响。毛细管流变学与PIV相结合的方法能够检测流动运动学中快速的空间和时间变化，这些变化与剪切增稠行为和SIS的动力学有关，但单纯的流变测量无法区分。发现该溶液有一条细节丰富的流动曲线，包括五个不同的区域。具体而言，在极低的剪切速率下呈现牛顿行为，随后在第二个区域出现剪切变稀。在第三个区域，观察到剪切带，它是SIS和剪切增稠的先兆。流动曲线的第四和第五个区域由类似突跃的行为分隔开，它们清楚地证明了剪切增稠的存在，同时伴随着流变仪壁处的粘滑振荡，这随后在剪切应力控制的流动下导致剪切速率发生变化。这种粘滑现象一直持续到本研究中使用的最高剪切应力，并且反映在具有与SIS的形成和破坏动力学相关的空间和时间变化的不对称速度分布中。流变仪壁处明显滑移的存在提供了一种能量释放机制，导致SIS的破坏，随后在循环的粘滞部分进一步重新形成。此外，PIV测量能够检测壁处的明显滑移以及流体主体中的机械故障，这表明剪切应力场对SIS动力学有额外贡献。增加流体在流动系统中的停留时间会增强剪切增稠行为。最后，详细描述了流动运动学并获得了真实的流动曲线，该曲线仅部分符合现有剪切增稠溶液理论模型的框架。
