Chemistry Division, Physical Chemistry and Applied Spectroscopy Group (C-PCS), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
J Am Chem Soc. 2010 Nov 17;132(45):16165-75. doi: 10.1021/ja106836f. Epub 2010 Oct 25.
Density gradient ultracentrifugation (DGU) and fluorescence spectroscopy are used to probe the limiting behaviors of the dynamic response of surfactant structure at the single-walled carbon nanotube (SWNT) surface to reorganizing forces, including changes in surfactant concentration and electrolyte screening. DGU results indicate that, as surfactant (sodium dodecyl sulfate, SDS) concentration is increased, SDS adsorbed on metallic SWNTs becomes limited in its ability to reorganize before SDS adsorbed on semiconducting species. A diameter-dependent enhancement is observed in photoluminescence intensities from semiconducting SWNTS upon initial titration with NaCl. This response to electrostatic screening diminishes as SDS concentration is increased. The results are understood as a saturation of the surfactant structural response, defined as both a loss in ability to increase SDS loading at the SWNT surface and a loss in ability to reorient surface structure in response to a reorganizing force. Saturation of response is found to be reversible and also occurs as a result of restricting SDS mobility. These results confirm several aspects of recent molecular dynamics simulations of SDS behavior on SWNTs and have important implications for tunability of density-based separation approaches using cosurfactant systems that include SDS.
密度梯度超速离心（DGU）和荧光光谱用于探测表面活性剂结构在单壁碳纳米管（SWNT）表面上对重组力的动态响应的极限行为，包括表面活性剂浓度和电解质屏蔽的变化。DGU 结果表明，随着表面活性剂（十二烷基硫酸钠，SDS）浓度的增加，在 SDS 吸附在半导体物种之前，吸附在金属 SWNT 上的 SDS 在重组能力方面受到限制。在初始滴定 NaCl 时，观察到来自半导体 SWNTS 的光致发光强度的直径依赖性增强。随着 SDS 浓度的增加，对静电屏蔽的这种响应会减弱。这些结果被理解为表面活性剂结构响应的饱和，定义为在 SWNT 表面上增加 SDS 负载的能力的丧失以及响应重组力重新定向表面结构的能力的丧失。发现响应的饱和是可逆的，并且也是由于限制 SDS 迁移率而发生的。这些结果证实了最近关于 SDS 在 SWNTs 上行为的分子动力学模拟的几个方面，并对使用包括 SDS 的助表面活性剂系统的基于密度的分离方法的可调节性具有重要意义。
