A thermo-sensitive supramolecular hydrogel derived from an onium salt with solution-gel-crystal transition properties
A thermo-sensitive supramolecular hydrogel derived from an onium salt with solution-gel-crystal transition properties
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一种源自鎓盐的热敏超分子水凝胶，具有溶液-凝胶-晶体转变特性
DOI：
10.1039/c6ra23761d
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发表时间：
2016-01-01
期刊：
影响因子：
3.9
通讯作者：
Luo, Xu-Zhong
中科院分区：
文献类型：
--
作者：
Jia, Xin-Jian;Wang, Jinshu;Luo, Xu-Zhong
采用扫描电镜、透射电镜、单晶X射线衍射、热重分析、差示扫描量热分析、流变实验、核磁共振氢谱、傅里叶变换红外光谱和粉末X射线衍射等方法研究了三聚氰胺在不同酸性条件下的凝胶能力，并对凝胶因子聚集体进行了表征。结果表明，三聚氰胺在水溶液中与多种有机/无机酸发生强烈的相互作用，形成了具有不同临界胶凝因子浓度（CGC）的热可逆超分子水凝胶。水杨酸、间羟基苯甲酸和对羟基苯甲酸的CGC值因空间位阻的存在而降低，而草酸和硼酸的CGC值因分子结构中缺少苯环而升高。更有趣的是，通过苯甲酸和三聚氰胺的刘易斯酸碱反应，形成了独特的鎓盐，2，4，6-三氨基-1，3，5-三嗪-1-鎓苯甲酸盐二水合物（TTIBD）。晶体属单斜晶系，空间群C2/c（Z = 8），晶格参数a = 21.477（3）埃，B = 10.2253（14）埃，c = 12.3312（17）埃，β = 98.717（3）度。所形成的水凝胶不仅表现出热敏特性和类固体行为，而且还表现出溶液-凝胶晶体转变，即无定形-结晶相转变。通过增加浓度从0.04到0.12 mol L-1，凝胶-溶液转变温度从23.0增加到49.5摄氏度，和凝胶-晶体转变时间从430减少到253分钟，但都在增加浓度后趋于平稳。TTIBD晶体沿着与相应的水凝胶通过氢键和π-π堆积相互作用自组装。
The gelation ability of melamine was evaluated under various acidic conditions, and the related gelator aggregates were investigated with scanning electron microscopy, transmission electron microscopy, single-crystal X-ray diffraction, thermo-gravimetric analysis, differential scanning calorimetric analysis, rheological experiments, 1H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and powder X-ray diffraction. It was found that melamine interacted strongly with a number of organic/inorganic acids in water, forming thermal-reversible supramolecular hydrogels with different critical gelator concentrations (CGCs). The CGCs of gelators successively made with salicylic acid, m-hydroxybenzoic acid and p-hydroxybenzoic acid decreased because of the steric hindrance, whereas those related to oxalic acid dihydrate and orthoboric acid presented higher values due to the lack of a phenyl ring in the molecular structures. More interestingly, a unique onium salt, 2,4,6-triamino-1,3,5-triazin-1-ium benzoate dihydrate (TTIBD), was formed via the Lewis acid-base reaction of benzoic acid and melamine. It crystallized in the monoclinic space group C2/c (Z = 8) with lattice parameters a = 21.477 (3) angstrom, b = 10.2253 (14) angstrom, c = 12.3312 (17) angstrom and beta = 98.717 (3)degrees. The formed hydrogel not only exhibited thermo-sensitive characteristics and solid-like behavior, but also showed a solution-gel crystal transition, being an amorphous-to-crystalline phase transition. By increasing the concentration from 0.04 to 0.12 mol L-1, the gel-solution transition temperature increased from 23.0 to 49.5 degrees C, and the gel-crystal transition time decreased from 430 to 253 min, but both leveled off upon increasing the concentration. The TTIBD crystal along with the corresponding hydrogel was self-assembled via hydrogen bonds and pi-pi stacking interactions.