We present experimental data and numerical modeling of a nonlinear phenomenon in active magnetic microbead rheology that appears to be common to entangled polymer solutions (EPS). Dynamic experiments in a modest range of magnetic forces show (1) a short-lived high viscosity plateau, followed by (2) a bead acceleration phase with a sharp drop in apparent viscosity, and (3) a terminal steady state that we show resides on the shear-thinning slope of the steady-state flow curve from cone and plate data. This latter feature implies a new protocol to access the nonlinear steady-state flow curve for biological EPS available only in microliter-scale volumes. We use the moment-closure form of the Rolie–Poly kinetic model for EPS hydrodynamics, together with a decoupling approximation that obviates the need for a full three-dimensional (3D) flow solver, to qualitatively reproduce this dynamic experimental sequence. We thereby explain the phenomenon in terms of entangled polymer physics, and show how the nonlinear event (acceleration and termination on the shear-thinning response curve) is tunable by the interplay between molecular-scale mechanisms (relaxation via reptation and chain retraction) and magnetic force controls. The experimental conditions mimic movement of cilia tips, bacteria, and sperm in mucus barriers, implying a physiological relevance of the phenomenon and compelling further quantitative kinetic-flow 3D numerical modeling.

中文翻译：

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缠结聚合物溶液活性微珠流变学的非线性特征

我们提供了活性磁微珠流变学中非线性现象的实验数据和数值建模，这种现象似乎在缠结聚合物溶液 (EPS) 中很常见。在适度磁力范围内的动态实验显示 (1) 短暂的高粘度平台，然后是 (2) 珠加速阶段，表观粘度急剧下降，以及 (3) 我们显示的最终稳态从锥板数据得到稳态流动曲线的剪切稀化斜率。后一个功能意味着一种新的协议，可以访问仅在微升级体积中可用的生物 EPS 的非线性稳态流动曲线。我们将 Rolie-Poly 动力学模型的力矩闭合形式用于 EPS 流体动力学，并结合解耦近似，从而无需完整的三维 (3D) 流动求解器，定性地重现这个动态实验序列。因此，我们从纠缠聚合物物理学的角度解释了这一现象，并展示了非线性事件（剪切稀化响应曲线上的加速和终止）如何通过分子尺度机制（通过蠕动和链回缩而松弛）和磁性之间的相互作用进行调节。力控制。实验条件模拟了粘液屏障中纤毛尖端、细菌和精子的运动，暗示了该现象的生理相关性，并有必要进行进一步的定量动力学流 3D 数值建模。并展示非线性事件（剪切稀化响应曲线上的加速和终止）如何通过分子尺度机制（通过蠕动和链收缩而松弛）和磁力控制之间的相互作用进行调节。实验条件模拟了粘液屏障中纤毛尖端、细菌和精子的运动，暗示了该现象的生理相关性，并有必要进行进一步的定量动力学流 3D 数值建模。并展示非线性事件（剪切稀化响应曲线上的加速和终止）如何通过分子尺度机制（通过蠕动和链收缩而松弛）和磁力控制之间的相互作用进行调节。实验条件模拟了粘液屏障中纤毛尖端、细菌和精子的运动，暗示了该现象的生理相关性，并有必要进行进一步的定量动力学流 3D 数值建模。