Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University , P.O. Box 16300, 00076 Aalto, Finland.
Chimie de la Matière Condensée de Paris, Sorbonne Universités , 75005, Paris, France.
Biomacromolecules. 2017 Jun 12;18(6):1975-1982. doi: 10.1021/acs.biomac.7b00463. Epub 2017 May 11.
The presence of an interface generally influences crystallization of polymers from melt or from solution. Here, by contrast, we explore the effect of surface immobilization in a direct solid state polymorphic transition on individual cellulose nanocrystals (CNCs), extracted from a plant-based origin. The conversion from native cellulose I to cellulose III crystal occurred via a host-guest inclusion of ethylene diamine inside the crystal. A 60% reduction in CNC width (height) in atomic force microscopy images suggested that when immobilized on a flat modified silica surface, the stresses caused by the inclusion or the subsequent regeneration resulted in exfoliation, hypothetically, between the van der Waals bonded sheets within the crystal. Virtually no changes in dimensions were visible when the polymorphic transition was performed to nonimmobilized CNCs in bulk dispersion. With reservations and by acknowledging the obvious dissimilarities, the exfoliation of cellulose crystal sheets can be viewed as analogous to exfoliation of 2D structures like graphene from a van der Waals stacked solid. Here, the detachment is triggered by an inclusion of a guest molecule inside a host cellulose crystal and the stresses caused by the firm attachment of the CNC on a solid substrate, leading to detachment of molecular sheets or stacks of sheets.
界面的存在通常会影响聚合物从熔体或溶液中的结晶。相比之下，我们在这里探索了在直接固态多晶型转变中表面固定化对单个纤维素纳米晶体（CNC）的影响，这些 CNC 是从植物来源中提取的。从天然纤维素 I 到纤维素 III 晶体的转变是通过乙二胺在晶体内部的主体-客体包合作用发生的。原子力显微镜图像中 CNC 宽度（高度）降低了 60%，这表明当固定在平坦的改性二氧化硅表面上时，包含物或随后的再生引起的应力导致剥离，假设在晶体中范德华键合的片层之间发生剥离。当在块状分散体中对非固定化的 CNC 进行多晶型转变时，实际上看不到尺寸的变化。有保留地并承认明显的差异，纤维素晶体片的剥离可以被视为类似于二维结构如石墨烯从范德华堆叠固体中的剥离。在这里，通过在主体纤维素晶体内部包含客体分子以及 CNC 在固体基底上的牢固附着引起的应力来触发脱离，导致分子片或片层的脱离。
