Fiber and Biopolymer Research Institute, Department of Plant and Soil Science, Texas Tech University , Lubbock, Texas 79409, United States.
Langmuir. 2016 Sep 27;32(38):9863-72. doi: 10.1021/acs.langmuir.6b02861. Epub 2016 Sep 14.
Cellulose nanocrystals (CNCs) are perfect rodlike nanofibers that can self-assemble and form a chiral nematic phase. We found that different self-assembling morphologies could be formed by different size-unified CNCs. This study reported a facile and new approach of fractionating raw (unseparated) CNCs in a wide particle size distribution (9-1700 nm) into a series of narrower size ranges to obtain size-unified CNCs via a well-designed multistage separation process composed of layered filter membranes with different pore size cutoffs followed by a fast pressurized filtration. The smaller size-unified CNCs readily self-assembled into polish chiral nematic phases with larger pitch value as compared to larger size-unified CNCs. Such a distinction among different chiral nematic phases and pitch values as functions of size was addressed by a mathematical evaluation, which suggested that the reduced volume fraction of the anisotropic phase as a function of both increased ionic strength and reduced crystallinity of rigid-rod-like CNCs is a critical factor. In addition, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction results revealed that different size-unified CNCs exhibited particular thermal stabilities and crystallinities even though their chemical and crystalline structures remained unchanged. The discrepancies in physicochemical characteristics and self-assembling chiral nematic behavior among different size-unified CNCs may benefit the specific functionalization of cellulose materials using size-unified fibers instead of raw CNCs containing mixed small and large fibers.
纤维素纳米晶（CNCs）是完美的棒状纳米纤维，可以自组装并形成手性向列相。我们发现不同的自组装形态可以通过不同尺寸均一的 CNCs 形成。本研究报道了一种简便的新方法，通过精心设计的多级分离过程，将原始（未分离）CNCs 在较宽的粒径分布（9-1700nm）中分离成一系列较窄的粒径范围，得到尺寸均一的 CNCs。该过程由具有不同孔径截止值的层状滤膜组成，随后进行快速加压过滤。与较大尺寸均一的 CNCs 相比，较小尺寸均一的 CNCs 更容易自组装成具有较大螺距值的抛光手性向列相。不同手性向列相和螺距值作为尺寸的函数之间的这种区别通过数学评估来解决，这表明作为离子强度增加和刚性棒状 CNCs 的结晶度降低的函数，各向异性相的体积分数减少是一个关键因素。此外，傅里叶变换红外光谱、热重分析和 X 射线衍射结果表明，即使化学和晶体结构保持不变，不同尺寸均一的 CNCs 也表现出特定的热稳定性和结晶度。不同尺寸均一的 CNCs 在物理化学特性和自组装手性向列行为上的差异可能有助于使用尺寸均一的纤维对手性向列行为进行特定的功能化，而不是使用含有混合小纤维和大纤维的原始 CNCs。
