Extensional viscosity is a key property of complex fluids that greatly influences the non-equilibrium behavior and processing of polymer solutions, melts, and colloidal suspensions. In this work, we use microfluidics to determine steady extensional viscosity for polymer solutions by directly observing particle migration in planar extensional flow. Tracer particles are suspended in semi-dilute solutions of DNA and polyethylene oxide, and a Stokes trap is used to confine single particles in extensional flows of polymer solutions in a cross-slot device. Particles are observed to migrate in the direction transverse to flow due to normal stresses, and particle migration is tracked and quantified using a piezo-nanopositioning stage during the microfluidic flow experiment. Particle migration trajectories are then analyzed using a second-order fluid model that accurately predicts that migration arises due to normal stress differences. Using this analytical framework, extensional viscosities can be determined from...

中文翻译：

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用于测定拉伸粘度的被动非线性微流变学

拉伸粘度是复杂流体的一个关键特性，它极大地影响聚合物溶液、熔体和胶体悬浮液的非平衡行为和加工。在这项工作中，我们使用微流体通过直接观察平面拉伸流中的粒子迁移来确定聚合物溶液的稳定拉伸粘度。示踪粒子悬浮在 DNA 和聚环氧乙烷的半稀释溶液中，斯托克斯阱用于将单个粒子限制在交叉槽装置中聚合物溶液的延伸流中。由于法向应力，观察到粒子在横向于流动的方向上迁移，并且在微流体流动实验期间使用压电纳米定位阶段跟踪和量化粒子迁移。然后使用二阶流体模型分析粒子迁移轨迹，该模型准确预测迁移是由法向应力差异引起的。使用这个分析框架，拉伸粘度可以从...