Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, 02139, USA.
Phys Rev Lett. 2012 Sep 21;109(12):128301. doi: 10.1103/PhysRevLett.109.128301. Epub 2012 Sep 17.
A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wi(crit) ≈ 0.5. Birefringence and bulk pressure drop measurements provide self-consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s(-1) ≤ ε ≤ 435 s(-1)) and are also in close agreement with numerical simulations performed by using a finitely extensible nonlinear elastic dumbbell model.
制造了一种经过数值模拟优化的精密机械交叉狭缝流动几何形状，并将其用于测量稀聚合物溶液的拉伸粘度。全场双折射显微镜用于监测在停滞点流线沿线大分子各向异性的演化和增长，当无量纲流动强度超过临界 Weissenberg 数 Wi(crit) ≈ 0.5 时，我们观察到形成强且均匀的双折射链。双折射和体相压降测量提供了在广泛的变形速率（26 s(-1) ≤ ε ≤ 435 s(-1)）下流体的平面拉伸粘度的自洽估计，并且与使用有限可伸展非线性弹性哑铃模型进行的数值模拟也非常吻合。
