AI 中文总结
该研究通过实验结合分析，揭示微流体共流中限域粘弹性丝的破裂受耦合壁-剪切-弹性机制控制，建立了相关预测框架，明确了四种流型及失稳规律。
AI 中文摘要
粘弹性丝的细缩经典上由拉伸流中的弹性毛细管动力学描述，但在限域微通道中，壁诱导剪切、弹性和毛细作用的耦合效应仍知之甚少。本文在矩形微通道中实验研究了一种剪切变稀粘弹性液体与不混溶牛顿流体共流时的破裂过程，重点关注连接主液滴与上游液体的细丝的形成、拉伸、失稳和破裂。利用分散相和连续相的毛细管数以及弹性毛细管参数，识别并绘制了四种流型：稳定共流、挤压、滴流和射流。尽管弹性对主液滴形成的起始影响较弱，但它通过延迟毛细破裂并稳定长寿命丝强烈改变了后续的丝动力学。基于毛细管、粘性和弹性力平衡的尺度分析预测了主液滴尺寸、失稳起始时的临界丝厚度、最大丝长度和临界射流长度。粒子跟踪显示，限域在倾斜的丝上产生了非均匀的壁诱导剪切场，导致界面速度的空间变化，并在最大剪切位置引发了首个串珠状失稳。结合Oldroyd-B模型推导的有效粘度的瑞利-普拉托分析，预测了失稳波长和增长率的正确数量级。这些结果表明，限域粘弹性破裂并非仅由经典弹性毛细管细缩控制，而是由耦合壁-剪切-弹性机制控制丝的拉伸、失稳和次级液滴形成，从而为限域粘弹性多相流中丝介导的破裂提供了预测框架。
英文摘要
Viscoelastic filament thinning is classically described by elastocapillary dynamics in extensional flows, yet in confined microchannels the combined effects of wall-induced shear, elasticity, and capillarity remain poorly understood. Here, we experimentally investigate the breakup of a shear-thinning viscoelastic liquid coflowing with an immiscible Newtonian fluid in a rectangular microchannel, focusing on the formation, stretching, instability, and breakup of the thin filament connecting the primary droplet to the upstream liquid. Four regimes: stable coflow, squeezing, dripping, and jetting are identified and mapped using the capillary numbers of the dispersed and continuous phases and an elastocapillary parameter. Although elasticity weakly affects the onset of primary droplet formation, it strongly alters later filament dynamics by delaying capillary breakup and stabilising long-lived filaments. Scaling analyses based on capillary, viscous, and elastic force balances predict the primary droplet size, critical filament thickness at instability onset, maximum filament length, and critical jet length. Particle tracking shows that confinement creates a non-uniform wall-induced shear field along the inclined filament, producing spatial variations in interfacial velocity and initiating the first bead-on-a-string instability at the location of maximum shear. A Rayleigh-Plateau analysis incorporating an effective viscosity derived from the Oldroyd-B model predicts the instability wavelength and growth rate to the correct order of magnitude. These results show that confined viscoelastic breakup is governed not solely by classical elastocapillary thinning, but by a coupled wall-shear-elasticity mechanism controlling filament stretching, instability, and secondary droplet formation, thereby providing a predictive framework for filament-mediated breakup in confined viscoelastic multiphase flows.
