Rosén Tomas, Wang Ruifu, Zhan Chengbo, He Hongrui, Chodankar Shirish, Hsiao Benjamin S
Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, USA.
Treesearch, KTH Royal Institute of Technology, 10044 Stockholm, Sweden.
Phys Rev E. 2020 Mar;101(3-1):032610. doi: 10.1103/PhysRevE.101.032610.
Nanostructured materials made through flow-assisted assembly of proteinaceous or polymeric nanosized fibrillar building blocks are promising contenders for a family of high-performance biocompatible materials in a wide variety of applications. Optimization of these processes relies on improving our knowledge of the physical mechanisms from nano- to macroscale and especially understanding the alignment of elongated nanoparticles in flows. Here, we study the full projected orientation distributions of cellulose nanocrystals (CNCs) and nanofibrils (CNFs) in confined flow using scanning microbeam SAXS. For CNCs, we further compare with a simulated system of dilute Brownian ellipsoids, which agrees well at dilute concentrations. However, increasing CNC concentration to a semidilute regime results in locally arranged domains called tactoids, which aid in aligning the CNC at low shear rates, but limit alignment at higher rates. Similarly, shear alignment of CNF at semidilute conditions is also limited owing to probable bundle or flock formation of the highly entangled nanofibrils. This work provides a quantitative comparison of full projected orientation distributions of elongated nanoparticles in confined flow and provides an important stepping stone towards predicting and controlling processes to create nanostructured materials on an industrial scale.
通过蛋白质或聚合物纳米级纤维状构建块的流动辅助组装制备的纳米结构材料，有望成为一系列高性能生物相容性材料，可用于广泛的应用领域。这些工艺的优化依赖于增进我们对从纳米到宏观尺度物理机制的了解，特别是理解细长纳米颗粒在流动中的排列。在这里，我们使用扫描微束小角X射线散射研究了受限流动中纤维素纳米晶体（CNC）和纳米纤维（CNF）的全投影取向分布。对于CNC，我们进一步与稀释布朗椭球体的模拟系统进行比较，在稀释浓度下二者吻合良好。然而，将CNC浓度增加到半稀释状态会导致形成称为类晶体的局部排列区域，这有助于在低剪切速率下使CNC排列，但在较高速率下会限制排列。同样，由于高度缠结的纳米纤维可能形成束或团簇，CNF在半稀释条件下的剪切排列也受到限制。这项工作对受限流动中细长纳米颗粒的全投影取向分布进行了定量比较，并为预测和控制工业规模制备纳米结构材料的过程提供了重要的垫脚石。
