Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge Massachusetts 02139, USA.
Phys Rev Lett. 2010 Aug 20;105(8):084501. doi: 10.1103/PhysRevLett.105.084501. Epub 2010 Aug 19.
We present the first direct evidence of flow-concentration coupling in a shear-banding fluid using the first measurements of scanning narrow-aperture flow ultrasmall-angle neutron scattering. Transmission measurements in the flow-gradient shear plane determine the spatial concentration profile of the material. Shear banding in a model fluid composed of wormlike micelles near an equilibrium isotropic-nematic transition is shown to be concomitant with shear-induced demixing, providing new insight into the nonequilibrium phase behavior of the fluid. The new experimental approach and analysis apply generally to any fluid, and will enable more rigorous testing of theories for shear-banding and shear-induced phase separation.
我们使用首次测量的扫描窄缝流超小角中子散射，提供了在剪切带流中流动-浓度耦合的首个直接证据。在流-梯度剪切面中的传输测量确定了材料的空间浓度分布。我们展示了由接近平衡各向同性-向列相转变的蠕虫状胶束组成的模型流体中的剪切带化与剪切诱导的分相同时发生，这为该流体的非平衡相行为提供了新的认识。新的实验方法和分析普遍适用于任何流体，将能够更严格地检验剪切带和剪切诱导相分离的理论。
