Institute of Chemical Industry of Forestry Products, CAF, Nanjing 210042, China.
J Colloid Interface Sci. 2012 Sep 15;382(1):53-60. doi: 10.1016/j.jcis.2012.06.005. Epub 2012 Jun 15.
Hydrogen bonds are strong intermolecular interactions, which are very important in molecular aggregation and new phase formation. Three long-chain quaternary ammonium surfactants, N,N-diethyl-N-(2-hydroxyethyl)-N-octadecylammonium bromide with one hydroxyl group, N-ethyl-N,N-bis (2-hydroxyethyl)-N-octadecylammonium bromide with two hydroxyl groups and N,N,N-tris (2-hydroxyethyl)-N-octadecylammonium bromide with three hydroxyl groups, abbreviated as SHQ, DHQ, and THQ, respectively, were synthesized in this work. Their solution behavior and solid phase transitions were investigated by surface tension, differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarizing optical microscopy (POM), and Infrared (IR) spectroscopy. The hydrogen bonds introduced by the substituted hydroxyl groups promoted surfactant adsorption at the air/water interface and aggregation in solution. In the crystal state, an increased number of hydroxyl groups caused a larger tilt angle of the long axis of surfactant molecules with the layer normal. Above certain temperatures, SHQ and DHQ formed highly ordered smectic T and smectic A phases while THQ only formed less ordered smectic A phase. The weakened electrostatic attractions between opposite ions and the thicker polar sublayers of mesophases caused by the enhanced number of hydrogen bonds are responsible for the mesophase formation and transition of these surfactants.
氢键是强的分子间相互作用，在分子聚集和新相形成中非常重要。本工作合成了三种长链季铵盐表面活性剂，分别带有一个羟基的 N,N-二乙基-N-(2-羟乙基)-N-十八烷基溴化铵（SHQ）、带有两个羟基的 N-乙基-N,N-双(2-羟乙基)-N-十八烷基溴化铵（DHQ）和带有三个羟基的 N,N,N-三(2-羟乙基)-N-十八烷基溴化铵（THQ）。通过表面张力、差示扫描量热法（DSC）、X 射线衍射（XRD）、偏光显微镜（POM）和红外（IR）光谱研究了它们的溶液行为和固相转变。取代羟基引入的氢键促进了表面活性剂在气/水界面的吸附和在溶液中的聚集。在晶体状态下，羟基数量的增加导致表面活性剂分子长轴与层法线的倾斜角度增大。在一定温度以上，SHQ 和 DHQ 形成了高度有序的近晶 T 相和近晶 A 相，而 THQ 仅形成了较无序的近晶 A 相。氢键数量的增加导致相间静电吸引力减弱和极性亚层变厚，这是这些表面活性剂形成和转变为介相的原因。
