Shear-banding in entangled xanthan solutions: tunable transition from sharp to broad shear-band interfaces.
Shear-banding in entangled xanthan solutions: tunable transition from sharp to broad shear-band interfaces.
复制标题
纠缠黄原胶溶液中的剪切带：从尖锐剪切带界面到宽剪切带界面的可调过渡。
作者：
H. Tang;H. Tang;T. Kochetkova;Hartmut Kriegs;J. Dhont;J. Dhont;M. Lettinga;M. Lettinga
我们报道了具有尖锐界面的梯度带状速度分布和弯曲速度分布之间的平滑过渡，这两者都是由于浓集型黄原胶(一种高带电多糖)的强烈剪切稀疏分散而产生的。在有限的剪切速率范围内，在很低的离子强度和很高的浓度下，观察到明显的剪切带流动，其中两个扩展的剪切带被相对尖锐的界面分开，使用外差光散射测量空间分辨的速度分布。通过改变剪切速率、降低浓度或增加离子强度，共存剪切带之间的界面宽度变宽，以跨越相当大一部分剪切单元的间隙。加宽导致了向高度弯曲的速度分布的平滑过渡，并与消失的流动双折射有关。因此，这些实验表明，经典的剪切带不稳定性可以引起高度弯曲的速度剖面，这是由于带之间存在宽的界面，其程度为数量级或大于胞隙宽度。这一观察结果可能有助于解决目前关于高度纠缠的聚合物体系剪切带化的争论，表明过去观察到的弯曲速度分布实际上是具有异常宽界面的剪切带态。
We report on the smooth transition between gradient-banded velocity profiles with a sharp interface and curved velocity profiles, both resulting from strong shear-thinning dispersions of concentrated xanthan (a highly charged poly-saccharide). Pronounced shear-banded flow, where two extended shear-bands are separated by a relatively sharp interface, is observed in a limited range of shear rates, at very low ionic strength and at a high concentration, using heterodyne light scattering to measure spatially resolved velocity profiles. The width of the interface between the coexisting shear-bands broadens to span a sizable fraction of the gap of the shear cell, either by changing the shear rate, by lowering the concentration, or by increasing the ionic strength. The broadening results in a smooth transition to highly curved velocity profiles and is connected to a disappearing flow birefringence. Thus, these experiments show that the classic shear-banding instability can give rise to highly curved velocity profiles, due to the existence of broad interfaces between the bands, with an extent of the order or larger than the cell gap width. This observation may aid to resolve the ongoing dispute concerning shear-banding of highly entangled polymeric systems, suggesting that the curved velocity profiles that have been observed in the past are in fact shear-banded states with an unusually broad interface.
影响因子：
3.3
作者：
Adams, J. M.;Fielding, S. M.;Olmsted, P. D.
通讯作者：
Olmsted, P. D.