论文标题
将剪切和伸展流对胶体杆排列的影响解耦
Decoupling the effects of shear and extensional flows on the alignment of colloidal rods
论文作者
论文摘要
纤维素纳米晶体（CNC）可以视为模型胶体棒，并在形成具有定制各向异性的软材料中具有实际应用。在这里，我们采用两个对比的微流体设备来定量阐明剪切和伸展流在稀释CNC分散剂对齐中的作用。通过微粒子图像速度法对流场的表征耦合到流动诱导的双重分析，以量化变形速率 - 对准关系。 CNC对准所需的变形率是4 $ \ times $的扩展率，而剪切速率比剪切较小。扩展中的对齐与变形速率的幅度无关，但根据其符号为0 $^\ circ $或90 $^\ circ $。在剪切流中，随着变形速率幅度的增加，胶体杆逐渐向0 $^\ Circ $定向。我们的结果将剪切和伸展运动学对对齐胶体杆的影响解散，从而确立了结构化软材料制造的连贯指南。
Cellulose nanocrystals (CNC) can be considered as model colloidal rods and have practical applications in the formation of soft materials with tailored anisotropy. Here, we employ two contrasting microfluidic devices to quantitatively elucidate the role of shearing and extensional flows on the alignment of a dilute CNC dispersion. Characterization of the flow field by micro-particle image velocimetry is coupled to flow-induced birefringence analysis to quantify the deformation rate--alignment relationship. The deformation rate required for CNC alignment is 4$\times$ smaller in extension than in shear. Alignment in extension is independent of the deformation rate magnitude, but is either 0$^\circ$ or 90$^\circ$ to the flow, depending on its sign. In shear flow the colloidal rods orientate progressively towards 0$^\circ$ as the deformation rate magnitude increases. Our results decouple the effects of shearing and extensional kinematics at aligning colloidal rods, establishing coherent guidelines for the manufacture of structured soft materials.
