CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, CAS Center for Excellence in Complex System Mechanics, University of Science and Technology of China, Hefei 230027, China.
CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, CAS Center for Excellence in Complex System Mechanics, University of Science and Technology of China, Hefei 230027, China.
Carbohydr Polym. 2021 Dec 1;273:118578. doi: 10.1016/j.carbpol.2021.118578. Epub 2021 Aug 20.
Sharp bends can be widely observed in isolated cellulose nanofibrils (CNFs) after mechanical treatment, referred to as kink dislocations that are previously found in wood cell walls under compression. The non-Gaussian distribution of kink angle implies some inherent deformation behaviors of cellulose nanocrystals (CNCs) hidden in the formation of kink dislocations in CNFs. We herein perform molecular dynamics simulations to investigate the kink deformation of nanocellulose. It is interesting to find an intrinsic deformation mode of Iβ CNCs under uniaxial compression, in which the metastable structure of kinked CNCs turns out to be the triclinic Iα phase with twin boundaries originated from interlayer dislocation-induced allomorphic transition. An intrinsic kink angle (~60°) is defined based on geometric traits of stable kinked CNCs. Moreover, the weakened intrachain hydrogen bonds in twin boundaries lead to exposed glycosidic bonds and damaged hydrogen-bonding networks, which would act as the origin of kink defects in nanocellulose.
在机械处理后，可以在分离的纤维素纳米纤维（CNF）中广泛观察到尖锐的弯曲，这些弯曲被称为扭结位错，此前在木材细胞壁受压时也有发现。扭结角的非高斯分布意味着在 CNF 中扭结位错的形成过程中隐藏着纤维素纳米晶体（CNC）的一些固有变形行为。本文通过分子动力学模拟来研究纳米纤维素的扭结变形。有趣的是，我们发现了单轴压缩下 Iβ CNC 的固有变形模式，其中扭结 CNC 的亚稳态结构原来是具有孪晶边界的三斜晶系 Iα 相，这些孪晶边界源自层间位错诱导的同型转变。基于稳定扭结 CNC 的几何特征，定义了内在扭结角（~60°）。此外，孪晶边界处的链内氢键减弱，导致糖苷键暴露和氢键网络受损，这将成为纳米纤维素中扭结缺陷的起源。
