Cornell High Energy Synchrotron Source (CHESS) , Ithaca , New York 14853 , United States.
Langmuir. 2018 May 8;34(18):5263-5272. doi: 10.1021/acs.langmuir.7b04403. Epub 2018 Apr 23.
In this manuscript, we report on the ordering of the cellulose nanocrystals (CNCs) as they experience shear forces during the casting process. To achieve these measurements, in situ and in real time, we used synchrotron-based grazing incidence wide-angle X-ray scattering (GIWAX). We believe that the GIWAX technique, although not commonly used to probe these types of phenomena, can open new avenues to gain deeper insights into film formation processes and surface-driven phenomena. In particular, we investigated the influence of solution concentration, shear-cast velocity, and drying temperature on the ordering of cellulose nanocrystals (CNCs) using GIWAXS. The films were prepared from aqueous suspensions of cellulose nanocrystals at two concentration values (7 and 9 wt %). As the films were cast, the X-ray beam was focused on a fixed position and GIWAXS patterns were recorded at regular time intervals. Structural characterization of the dry films was carried out via polarized optical microscopy and scanning electron microscopy. In addition, a rheological study of the CNC suspensions was performed. Our results show that the morphology of the CNC films was significantly influenced by shear velocity, concentration of the precursor suspension, and evaporation temperature. In contrast, we observed that the orientation parameter of the films was not significantly affected. The scattering intensity of the peak (200) was analyzed as a function of time, following a sigmoidal profile, hence indicating short- and long-range interactions within the anisotropic domains as they reached their final orientation state. A model capable of describing the resulting film morphologies is also proposed. The results and analysis presented in this manuscript provide new insights into the controlled alignment of cellulose nanocrystals under shear. This controlled alignment has significant implications in the development of advanced coatings and films currently used in a myriad of applications, such as catalysis, optics, electronics, and biomedicine.
在本文中，我们报告了纤维素纳米晶体（CNC）在铸造过程中经历剪切力时的有序排列。为了实现这些测量，我们使用基于同步加速器的掠入射广角 X 射线散射（GIWAXS）进行原位和实时测量。我们相信，尽管 GIWAX 技术通常不用于探测这些类型的现象，但它可以开辟新的途径，深入了解薄膜形成过程和表面驱动现象。特别是，我们使用 GIWAXS 研究了溶液浓度、剪切铸造速度和干燥温度对纤维素纳米晶体（CNC）有序排列的影响。这些薄膜是由纤维素纳米晶体在两种浓度值（7 和 9wt%）的水溶液中制备的。当薄膜被浇铸时，X 射线束聚焦在一个固定位置，并在固定时间间隔记录 GIWAXS 图案。干膜的结构特征通过偏光显微镜和扫描电子显微镜进行了表征。此外，还对 CNC 悬浮液进行了流变学研究。我们的结果表明，CNC 薄膜的形态受到剪切速度、前体悬浮液浓度和蒸发温度的显著影响。相比之下，我们观察到薄膜的取向参数没有明显变化。随着时间的推移，对峰（200）的散射强度进行了分析，呈现出类正弦曲线的形态，因此表明各向异性域内的短程和长程相互作用，直至达到最终的取向状态。还提出了一个能够描述所得薄膜形态的模型。本文提出的结果和分析为纤维素纳米晶体在剪切下的可控排列提供了新的见解。这种可控排列对目前在催化、光学、电子和生物医学等众多应用中使用的先进涂料和薄膜的发展具有重要意义。
