Zhang Juan, Liu Cuiting, Hu Xinyue, Lv Qichao, Zhang Hongsheng, Pi Benxiang, Yang Zihao, Lin Meiqin
Unconventional Petroleum Research Institute, China University of Petroleum, Beijing 102249, P. R. China.
Soft Matter. 2021 Feb 15;17(5):1428-1436. doi: 10.1039/d0sm01744b.
Recently, inclusion complexes formed from cyclodextrins (CDs) and surfactants have been found to play complex and important roles in supramolecular self-assembly. In this work, the self-assembly of perfluorononanoic acid (PFNA)/γ-cyclodextrin (γ-CD) in aqueous solution was investigated. The sole PFNA solution assembled into spherical uni-lamellar vesicles under certain concentrations as revealed by freeze-fracture transmission electron microscopy (FF-TEM) images. Interestingly, when γ-CD was added into the PFNA solution, one novel kind of cyclodextrin-based hydrogel with a crystal-like structure was obtained. The morphology of the hydrogels was inerratic parallel hexahedron or regular hexahedron as revealed by optical microscopy and scanning electron microscopy (SEM) measurements. Furthermore, the hydrogels were transformed into crystalline precipitates, which were composed of highly uniform tetragonal sheets with excellent crystallinity and homogeneous size distribution just by changing the γ-CD concentration. More amazingly, the crystal-like hydrogels were sensitive to shear and switched to solutions in their morphology with bar-like and rod-like aggregates and smaller square sheets under different shear rates, and the hydrogel-solution transition behavior was a reversable process. 1H NMR, Fourier transform infrared (FT-IR) and wide-angle X-ray diffraction (WXRD) measurements were performed to lead us to propose the formation mechanism of the above aggregates. Hopefully, our studies will cast new light on the fundamental investigations into the self-assembly of supramolecular systems of fluorinated surfactants and CD molecules and provide a new idea for smart material design.
最近，人们发现由环糊精（CDs）和表面活性剂形成的包合物在超分子自组装中发挥着复杂而重要的作用。在这项工作中，研究了全氟壬酸（PFNA）/γ-环糊精（γ-CD）在水溶液中的自组装。冷冻断裂透射电子显微镜（FF-TEM）图像显示，在一定浓度下，单一的PFNA溶液组装成球形单分子层囊泡。有趣的是，当将γ-CD加入到PFNA溶液中时，得到了一种具有晶体状结构的新型环糊精基水凝胶。光学显微镜和扫描电子显微镜（SEM）测量表明，水凝胶的形态为不规则平行六面体或规则六面体。此外，仅通过改变γ-CD的浓度，水凝胶就转变为晶体沉淀物，其由高度均匀的四方片组成，具有优异的结晶度和均匀的尺寸分布。更令人惊讶的是，这种晶体状水凝胶对剪切敏感，在不同剪切速率下形态转变为具有棒状和杆状聚集体以及较小方形片的溶液，并且水凝胶-溶液转变行为是一个可逆过程。进行了1H NMR、傅里叶变换红外（FT-IR）和广角X射线衍射（WXRD）测量，以引导我们提出上述聚集体的形成机制。希望我们的研究将为含氟表面活性剂和CD分子超分子体系自组装的基础研究提供新的思路，并为智能材料设计提供新的理念。
