Ultrasound velocimetry in a shear-thickening wormlike micellar solution: Evidence for the coexistence of radial and vorticity shear bands
Ultrasound velocimetry in a shear-thickening wormlike micellar solution: Evidence for the coexistence of radial and vorticity shear bands
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剪切增稠蠕虫状胶束溶液中的超声测速：径向和涡度剪切带共存的证据
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发表时间：
2008
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影响因子：
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通讯作者：
P. Fischer
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文献类型：
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作者：
V. Herle;S. Manneville;P. Fischer
摘要。我们在Couette剪切细胞中使用高频超声测速仪对40mM十六烷基吡啶-水杨酸钠（CPyCl-NaSal）虫状胶束溶液进行了定点局部速度测量。所研究的蠕虫状溶液在应力控制环境下表现出牛顿、剪切减薄和剪切增厚的流变行为。先前在该体系剪切增厚区进行的流变学、流动可视化和小角度光/中子散射实验表明，沿着Couette几何轴存在应力驱动的透明和浑浊交替环或涡度带。通过局部速度测量，我们观察到在剪切减薄（应力平台）区域的Couette单元1mm间隙内存在均匀流动。在应力控制实验中，只有当溶液被剪切超过临界剪切应力（剪切-增厚区）时，我们才观察到Couette几何中具有径向或速度梯度剪切带特征的非均匀流动，其中转子附近有高剪切带，定子附近有弱剪切带。此外，在剪切增厚区进行的快速测量以捕捉局部速度的时间演变表明径向和涡度剪切带共存。然而，在流变仪的剪切速率控制模式下进行的相同测量并未显示出这种流变学复杂性。
Abstract.We carried out pointwise local velocity measurements on 40mM cetylpyridinium chloride-sodium salicylate (CPyCl-NaSal) wormlike micellar solution using high-frequency ultrasound velocimetry in a Couette shear cell. The studied wormlike solution exhibits Newtonian, shear-thinning and shear-thickening rheological behavior in a stress-controlled environment. Previous rheology, flow visualization and small-angle light/neutron scattering experiments in the shear-thickening regime of this system showed the presence of stress-driven alternating transparent and turbid rings or vorticity bands along the axis of the Couette geometry. Through local velocity measurements we observe a homogeneous flow inside the 1mm gap of the Couette cell in the shear-thinning (stress-plateau) region. Only when the solution is sheared beyond the critical shear stress (shear-thickening regime) in a stress-controlled experiment, we observe inhomogeneous flow characterized by radial or velocity gradient shear bands with a highly sheared band near the rotor and a weakly sheared band near the stator of the Couette geometry. Furthermore, fast measurements performed in the shear-thickening regime to capture the temporal evolution of local velocities indicate coexistence of both radial and vorticity shear bands. However the same measurements carried out in shear rate controlled mode of the rheometer do not show such rheological complexity.