School of Science, College of Science, Engineering and Health, RMIT University, Melbourne, Australia.
Faraday Discuss. 2017 Dec 14;206:29-48. doi: 10.1039/c7fd00148g.
The phase behaviour of n-alkylammonium (C6 to C16) nitrates and formates has been characterised using synchrotron small angle and wide angle X-ray scattering (SAXS/WAXS), differential scanning calorimetry (DSC), cross polarised optical microscopy (CPOM) and Fourier transform infrared spectroscopy (FTIR). The protic salts may exist as crystalline, liquid crystalline or ionic liquid materials depending on the alkyl chain length and temperature. n-Alkylammonium nitrates with n ≥ 6 form thermotropic liquid crystalline (LC) lamellar phases, whereas n ≥ 8 was required for the formate series to form this LC phase. The protic ionic liquid phase showed an intermediate length scale nanostructure resulting from the segregation of the polar and nonpolar components of the ionic liquid. This segregation was enhanced for longer n-alkyl chains, with a corresponding increase in the correlation length scale. The crystalline and liquid crystalline phases were both lamellar. Phase transition temperatures, lamellar d-spacings, and liquid correlation lengths for the n-alkylammonium nitrates and formates were compared with those for n-alkylammonium chlorides and n-alkylamines. Plateau regions in the liquid crystalline to liquid phase transition temperatures as a function of n for the n-alkylammonium nitrates and formates are consistent with hydrogen-bonding and cation-anion interactions between the ionic species dominating alkyl chain-chain van der Waals interactions, with the exception of the mid chained hexyl- and heptylammonium formates. The d-spacings of the lamellar phases for both the n-alkylammonium nitrates and formates were consistent with an increase in chain-chain layer interdigitation within the bilayer-based lamellae with increasing alkyl chain length, and they were comparable to the n-alkylammonium chlorides.
使用同步加速器小角和广角 X 射线散射 (SAXS/WAXS)、差示扫描量热法 (DSC)、交叉偏振光学显微镜 (CPOM) 和傅里叶变换红外光谱 (FTIR) 研究了 C6 至 C16 的正烷基铵 (C6 至 C16) 硝酸盐和甲酸盐的相行为。质子盐的存在形式取决于烷基链长度和温度，可以是结晶、液晶或离子液体材料。正烷基铵硝酸盐中 n ≥ 6 形成热致液晶 (LC) 层状相，而对于甲酸盐系列，n ≥ 8 是形成该 LC 相所必需的。质子离子液体相表现出中间尺度的纳米结构，这是由于离子液体的极性和非极性成分的分离所致。对于较长的 n-烷基链，这种分离得到增强，相应地增加了相关长度尺度。结晶和液晶相均为层状相。比较了正烷基铵硝酸盐和甲酸盐的相转变温度、层状 d 间距和液体相关长度与正烷基铵氯化物和正烷基胺的相转变温度、层状 d 间距和液体相关长度。正烷基铵硝酸盐和甲酸盐的液晶相到液相转变温度随 n 的增加出现平台区域，这与离子物种之间的氢键和阳离子-阴离子相互作用以及支配烷基链-链范德华相互作用有关，除了中间链长的己基和庚基甲酸盐。正烷基铵硝酸盐和甲酸盐的层状相的 d 间距与双层基层状片中的链-链层间相互插入随烷基链长度的增加而增加一致，并且与正烷基铵氯化物相当。
