Rosén Tomas, Wang Ruifu, He HongRui, Zhan Chengbo, Chodankar Shirish, Hsiao Benjamin S
Department of Chemistry, Stony Brook University Stony Brook New York 11794-3400 USA
Department of Fiber and Polymer Technology, KTH Royal Institute of Technology SE-100 44 Stockholm Sweden.
Nanoscale Adv. 2021 Jul 19;3(17):4940-4951. doi: 10.1039/d1na00236h. eCollection 2021 Aug 25.
During the past decade, cellulose nanofibrils (CNFs) have shown tremendous potential as a building block to fabricate new advanced materials that are both biocompatible and biodegradable. The excellent mechanical properties of the individual CNF can be transferred to macroscale fibers through careful control in hydrodynamic alignment and assembly processes. The optimization of such processes relies on the understanding of nanofibril dynamics during the process, which in turn requires characterization. Here, we use a shear-free mixing experiment combined with scanning small-angle X-ray scattering (scanning-SAXS) to provide time-resolved nanoscale kinetics during the assembly of dispersed cellulose nanofibrils (CNFs) upon mixing with a sodium chloride solution. The addition of monovalent ions led to the transition to a volume-spanning arrested (gel) state. The transition of CNFs is associated with segmental aggregation of the particles, leading to a connected network and reduced Brownian motion, whereby an aligned structure can be preserved. Furthermore, we find that the extensional flow seems to enhance the formation of these segmental aggregates, which in turn provides a comprehensible explanation for the superior material properties obtained in shear-free processes used for spinning filaments from CNFs. This observation clearly highlights the need for different assembly strategies depending on morphology and interactions of the dispersed nanoparticles, where this work can be used as a guide for improved nanomaterial processes.
在过去十年中，纤维素纳米原纤维（CNFs）作为构建新型先进材料的基础材料展现出了巨大潜力，这些材料兼具生物相容性和生物可降解性。通过在流体动力排列和组装过程中进行仔细控制，单个CNF的优异机械性能可以传递到宏观尺度的纤维上。此类过程的优化依赖于对过程中纳米原纤维动力学的理解，而这又需要进行表征。在此，我们采用无剪切混合实验结合扫描小角X射线散射（扫描SAXS），以提供在分散的纤维素纳米原纤维（CNFs）与氯化钠溶液混合组装过程中的时间分辨纳米尺度动力学。单价离子的添加导致转变为体积跨度受阻（凝胶）状态。CNFs的转变与颗粒的片段聚集有关，导致形成连通网络并减少布朗运动，借此可以保留排列结构。此外，我们发现拉伸流动似乎会增强这些片段聚集体的形成，这反过来为在用于从CNFs纺丝的无剪切过程中获得的优异材料性能提供了一个可理解的解释。这一观察结果清楚地凸显了根据分散纳米颗粒的形态和相互作用采用不同组装策略的必要性，这项工作可作为改进纳米材料过程的指南。
