Nativ-Roth Einat, Yerushalmi-Rozen Rachel, Regev Oren
Department of Chemical Engineering, Ben-Gurion University of the Negev Beer Sheva 84105, Israel.
Small. 2008 Sep;4(9):1459-67. doi: 10.1002/smll.200800082.
The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions is investigated at room temperature. Small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) are used for characterization of bulk dispersions and nanometrically thin films. Additional carbonaceous additives (fullerenes, multi-walled carbon nanotubes, and carbon black) serve as reference systems. It is found that dispersions of carbonaceous additive (excluding fullerenes) at intermediate surfactant concentrations (below the liquid-crystalline region of the native surfactant) induce demixing and macroscopic phase separation in otherwise homogeneous solutions of CTAB. Two coexisting liquid phases of similar CTAB concentrations are observed, with the carbonaceous species residing within the lower phase. At high CTAB concentrations (liquid-crystal region) the SWNTs are found to incorporate into the ordered lyotropic liquid-crystalline phase while preserving the native d-spacing. Investigation of nanometrically thin films at intermediate surfactant concentrations under external shear reveals shear-induced structure (SIS) in the presence of minute amounts of SWNTs. The effect is found to be exclusive to SWNT and does not occur in dispersions of other carbonaceous additives.
室温下，研究了单壁碳纳米管（SWNT）对阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）水溶液相行为的影响。小角X射线散射（SAXS）和低温透射电子显微镜（cryo-TEM）用于表征本体分散体和纳米级薄膜。其他含碳添加剂（富勒烯、多壁碳纳米管和炭黑）用作参考体系。研究发现，在中间表面活性剂浓度下（低于天然表面活性剂的液晶区域），含碳添加剂（不包括富勒烯）的分散体在原本均匀的CTAB溶液中会引起分层和宏观相分离。观察到两个CTAB浓度相似的共存液相，含碳物质存在于下层相中。在高CTAB浓度下（液晶区域），发现SWNTs会融入有序的溶致液晶相，同时保持天然的d间距。在外部剪切作用下，对中间表面活性剂浓度下的纳米级薄膜进行研究，发现在存在微量SWNTs的情况下会出现剪切诱导结构（SIS）。发现这种效应是SWNT独有的，在其他含碳添加剂的分散体中不会出现。
