Feng Tao, Hoagland David A, Russell Thomas P
Department of Polymer Science and Engineering, University of Massachusetts-Amherst , Amherst, Massachusetts 01003, United States.
Langmuir. 2014 Feb 4;30(4):1072-9. doi: 10.1021/la404543s. Epub 2014 Jan 21.
The efficient segregation of water-soluble, acid-functionalized, single-walled carbon nanotubes (SWCNTs) at the oil/water interface was induced by dissolving low-molecular-weight amine-terminated polystyrene (PS-NH2) in the oil phase. Salt-bridge interactions between carboxylic acid groups of SWCNTs and amine groups of PS drove the assembly of SWCNTs at the interface, monitored by pendant drop tensiometry and laser scanning confocal microscopy. The impact of PS end-group functionality, PS and SWCNT concentrations, and the degree of SWCNT acid modification on the interfacial activity was assessed, and a sharp drop in interfacial tension was observed above a critical SWCNT concentration. Interfacial tensions were low enough to support stable oil/water emulsions. Further experiments, including potentiometric titrations and the replacement of SWCNTs by other carboxyl-containing species, demonstrated that the interfacial tension drop reflects the loss of SWCNT charge as the pH falls near/below the intrinsic carboxyl dissociation constant; species lacking multivalent carboxylic acid groups are inactive. The trapped SWCNTs appear to be neither ordered nor oriented.
通过将低分子量胺封端的聚苯乙烯（PS-NH₂）溶解在油相中，可诱导水溶性、酸功能化的单壁碳纳米管（SWCNT）在油/水界面处有效分离。SWCNT的羧酸基团与PS的胺基团之间的盐桥相互作用促使SWCNT在界面处组装，通过悬滴张力测定法和激光扫描共聚焦显微镜进行监测。评估了PS端基官能团、PS和SWCNT浓度以及SWCNT酸修饰程度对界面活性的影响，并且在临界SWCNT浓度以上观察到界面张力急剧下降。界面张力足够低，能够支撑稳定的油/水乳液。进一步的实验，包括电位滴定以及用其他含羧基物种替代SWCNT，结果表明，随着pH值降至接近/低于固有羧基解离常数，界面张力下降反映了SWCNT电荷的损失；缺乏多价羧酸基团的物种没有活性。捕获的SWCNT似乎既没有有序排列也没有定向排列。
