论文标题

线性和分支虫状胶束中剪切带流的动力学的动力学

Kinetics of Shear Banding Flow Formation in Linear and Branched Wormlike Micelles

论文作者

Rassolov, Peter, Scigliani, Alfredo, Mohammadigoushki, Hadi

论文摘要

我们使用粒子跟踪的速度表,双重光和旋转度和滚动度测量的组合,研究了线性和分支类蠕虫样胶束溶液的流动演化。两种溶液在剪切速率范围内表现出应力平稳。在应力平台内稳定的剪切速率流的启动下,线性和分支样品均表现出强大的瞬态剪切稀薄流量。然而,尽管线性溶液的流动在更长的时间内演变为带状结构,但分支溶液的流向弯曲速度曲线的流动,没有剪切带的迹象。流动诱导的双重测量值表示线性溶液中高剪切带中具有强胶束比对的瞬态双重束带。在原本相同的WI处,分支系统的瞬态流动诱导的双折射更强。在更长的时候,双折带带被让人联想到弹性不稳定性的混乱流动所取代。速度梯度涡度平面中流动诱导的浊度的可视化揭示了准稳态带,线性溶液中高和低剪切带之间的浊度对比度。然而,浊度在TC细胞的间隙内均匀地演变为分支溶液,从而证实了非带状的准稳态速度测定结果。最后,我们表明,虽然线性溶液中的弹性不稳定性在高剪切带中出现,但由于最终效应,高WI处的分支溶液的流动变得不稳定,而生长的终端区域最终跨越了TC细胞的整个轴向长度。

We investigate the flow evolution of a linear and a branched wormlike micellar solution with matched rheology in a Taylor-Couette (TC) cell using a combination of particle-tracking velocimetry, birefringence, and turbidity measurements. Both solutions exhibit a stress plateau within a range of shear rates. Under startup of a steady shear rate flow within the stress plateau, both linear and branched samples exhibit strong transient shear thinning flow profiles. However, while the flow of the linear solution evolves to a banded structure at longer times, the flow of the branched solution transitions to a curved velocity profile with no evidence of shear banding. Flow-induced birefringence measurements indicate transient birefringence banding with strong micellar alignment in the high shear band for the linear solution. The transient flow-induced birefringence is stronger for the branched system at an otherwise identical Wi. At longer times, the birefringence bands are replaced by a chaotic flow reminiscent of elastic instabilities. Visualization of the flow-induced turbidity in the velocity gradient-vorticity plane reveals quasi-steady banding with a turbidity contrast between high and low shear bands in the linear solution. However, the turbidity evolves uniformly within the gap of the TC cell for the branched solution, corroborating the non-banded quasi-steady velocimetry results. Finally, we show that while elastic instabilities in the linear solution emerge in the high shear band, the flow of branched solution at high Wi becomes unstable due to end effects, with growing end regions that ultimately span the entire axial length of the TC cell.

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