Abstract Rheo-NMR velocimetry was used to study shear banding of a 6 wt.% cetylpyridinium chloride (CPCl) worm-like micelle solution under shear startup conditions with and without pre-shear. 1D velocity profiles across the fluid gap of a concentric cylinder Couette shear cell were measured every 1 s following shear startup for four different applied shear rates within the stress plateau. Fitting of the velocity profiles allowed calculation of the shear banding characteristics (shear rates in the high and low shear band, the interface position and apparent slip at the inner rotating wall) as the flow transitioned from transient to steady state regimes. Characteristic timescales to reach steady state were obtained and found to be similar for all shear banding characteristics. Timescales decreased with increasing applied shear rate. Large temporal fluctuations with time were also observed and Fourier transform of the time and velocity autocorrelation functions quantified the fluctuation frequencies. Frequencies corresponded to the elastically driven hydrodynamic instabilities, i.e. vortices, that are known to occur in the unstable high shear band and were dependent upon both applied shear rate and the pre-shear protocol.

中文翻译：

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Rheo-NMR 表征剪切启动下蠕虫状胶束溶液中具有和不具有预剪切的速度波动和从瞬态到稳态剪切带的转变

摘要 流变核磁共振测速仪用于研究 6 wt.% 氯化十六烷基吡啶 (CPCl) 蠕虫状胶束溶液在有和没有预剪切的剪切启动条件下的剪切带。在剪切启动后每 1 秒测量一次同心圆柱库埃特剪切单元流体间隙的一维速度分布，在应力平台内对四种不同的应用剪切速率进行测量。当流动从瞬态状态过渡到稳态状态时，速度剖面的拟合允许计算剪切带特征（高剪切带和低剪切带中的剪切速率、界面位置和内部旋转壁的表观滑移）。获得了达到稳定状态的特征时间尺度，发现所有剪切带特征都相似。时间尺度随着施加的剪切速率的增加而减少。还观察到随时间的大时间波动，并且时间和速度自相关函数的傅立叶变换量化了波动频率。频率对应于弹性驱动的流体动力学不稳定性，即涡流，已知发生在不稳定的高剪切带中并且取决于应用的剪切速率和预剪切协议。