Linear versus branched: flow of a wormlike micellar fluid past a falling sphere
Linear versus branched: flow of a wormlike micellar fluid past a falling sphere
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线性与支化：蠕虫状胶束流体流过下落的球体
DOI：
10.1039/d1sm00281c
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发表时间：
2021
期刊：
影响因子：
3.4
通讯作者：
Mohammadigoushki, Hadi
中科院分区：
文献类型：
--
作者：
Wu, Shijian;Mohammadigoushki, Hadi
我们报道了蠕虫状胶束溶液流过下落球体的实验。通过增加盐与表面活性剂的浓度比，并且超过粘度峰值，蠕虫状胶束经历从线性微结构到支化微结构的转变。两个粘弹性蠕虫状胶束与盐的粘度峰的每一侧的表面活性剂浓度被认为是。我们的研究结果表明三个显着的差异，支化和线性胶束的流量。首先，虽然球阻力校正因子在线性胶束中随着Weissenberg数的增加而迅速减小，但在支化胶束中在Wi = 3处显示出明显的局部最大值。第二，尽管其高粘弹性，时间平均流动的分支胶束周围的下降的球体表现出前后对称性，而一个强大的负尾流观察到在线性胶束在相对较弱的流量。第三，分支胶束表现出更强的流动诱导的双折射比线性胶束在其他相同的条件。我们的假设是，受到强大的流动周围的下降球，分支胶束可以放松更有效地比线性蠕虫状胶束通过滑动的分支路口。这种额外的应力松弛机制可以促进胶束取向，产生边缘球减阻和牛顿样的流动轮廓周围的下降球。最后，在线性和支化胶束溶液中观察到不稳定流动超过一些临界阈值的延伸Weissenber数。我们的研究结果证实了最近提出的标准蠕虫状胶束过去的下降球的流动不稳定的发病，从而表明胶束分支不影响流动不稳定的机制。
We report experiments on flow of wormlike micellar solutions past a falling sphere. By increasing the salt-to-surfactant concentration ratio, and beyond a viscosity peak, wormlike micelles experience a transition from linear to branched microstructure. Two viscoelastic wormlike micelles with salt to surfactant concentrations on each side of the viscosity peak are considered. Our results indicate three significant differences in flows of branched and linear micelles. First, while the sphere drag correction factor rapidly decreases upon increasing Weissenberg number in linear micelles, it shows an apparent local maximum at Wi ≈ 3 in branched micelles. Second, despite its high viscoelasticity, the time-averaged flow of branched micelles around the falling sphere exhibits a fore-and-aft symmetry, while a strong negative wake is observed in linear micelles at relatively weaker flows. Third, branched micelles exhibit a stronger flow-induced birefringence than linear micelles in an otherwise identical condition. Our hypothesis is that subject to strong flows around the falling sphere, branched micelles can relax much more efficiently than linear wormlike micelles through sliding of the branched junctions. This additional stress relaxation mechanism may facilitate micellar orientation, produce a marginal sphere drag reduction and a Newtonian-like flow profile around the falling sphere. Finally, unsteady flow is observed in both linear and branched micellar solutions beyond some critical thresholds of the extensional Weissenber number. Our results corroborate a recently proposed criterion for onset of instability in flow of wormlike micelles past a falling sphere, thereby, suggesting that micellar branching does not affect the mechanism of flow instability.