Xue Chun-Dong, Chen Xiao-Dong, Li Yong-Jiang, Hu Guo-Qing, Cao Tun, Qin Kai-Rong
School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian 116024, China.
School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China.
Micromachines (Basel). 2020 Apr 14;11(4):406. doi: 10.3390/mi11040406.
Droplet microfluidics involving non-Newtonian fluids is of great importance in both fundamental mechanisms and practical applications. In the present study, breakup dynamics in droplet generation of semi-dilute polymer solutions in a microfluidic flow-focusing device were experimentally investigated. We found that the filament thinning experiences a transition from a flow-driven to a capillary-driven regime, analogous to that of purely elastic fluids, while the highly elevated viscosity and complex network structures in the semi-dilute polymer solutions induce the breakup stages with a smaller power-law exponent and extensional relaxation time. It is elucidated that the elevated viscosity of the semi-dilute solution decelerates filament thinning in the flow-driven regime and the incomplete stretch of polymer molecules results in the smaller extensional relaxation time in the capillary-driven regime. These results extend the understanding of breakup dynamics in droplet generation of non-Newtonian fluids and provide guidance for microfluidic synthesis applications involving dense polymeric fluids.
涉及非牛顿流体的微滴微流控技术在基础机理和实际应用方面都具有重要意义。在本研究中，对微流控流动聚焦装置中半稀释聚合物溶液液滴生成过程中的破碎动力学进行了实验研究。我们发现，细丝变细经历了从流动驱动到毛细驱动状态的转变，这与纯弹性流体类似，而半稀释聚合物溶液中高度升高的粘度和复杂的网络结构导致破碎阶段具有较小的幂律指数和拉伸松弛时间。据阐明，半稀释溶液升高的粘度在流动驱动状态下减缓了细丝变细，而聚合物分子的不完全拉伸导致毛细驱动状态下的拉伸松弛时间较小。这些结果扩展了对非牛顿流体液滴生成中破碎动力学的理解，并为涉及致密聚合物流体的微流控合成应用提供了指导。
