Key Laboratory of Colloid and Interface Science, Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P. R. China.
University of Chinese Academy of Sciences , Beijing 100049, P. R. China.
Langmuir. 2017 Jul 25;33(29):7271-7280. doi: 10.1021/acs.langmuir.7b00997. Epub 2017 Jul 11.
A star-shaped oligomeric-like surfactant with variable oligomeric degrees has been formed with a four-arm carboxylate salt (4EOCOONa) and cationic single chain surfactant dodecyl trimethylammonium bromide (DTAB). The aggregation of the 4EOCOONa/(DTAB) complexes has been investigated by surface tension, electrical conductivity, isothermal titration microcalorimetry, ζ potential, dynamic light scattering, H NMR spectroscopy, and steady-state fluorescence measurements. The calorimetric result shows that 4EOCOONa interacts strongly with DTAB and each 4EOCOONa molecule binds with six DTAB molecules, wherein four DTAB molecules electrostatically bind to one 4EOCOONa molecule and additional two DTAB molecules further bind to the 4EOCOONa/(DTAB) complex by hydrophobic interaction. The critical micelle concentration (CMC) of the 4EOCOONa/(DTAB) complexes is remarkably lower than the CMC of DTAB, similar to synthesized star-shaped oligomeric surfactants. The micelle properties of the DTAB/4EOCOONa mixtures depend on the component changes of the 4EOCOONa/(DTAB) complexes. By increasing the DTAB/4EOCOONa molar ratio and/or concentration, the DTAB/4EOCOONa mixtures gradually form the complexes of 4EOCOO(DTA), 4EOCOO(DTA), 4EOCOO(DTA), 4EOCOO(DTA), and 4EOCOO(DTA), and the corresponding aggregates are small anionic micelles with loose molecular packing, and nearly nonionic or positively charged small micelles with more compact packing. Moreover, the positive charge of the small micelles increases with the increase of the concentration and the DTAB/4EOCOONa molar ratio. Therefore, constructing oligomeric-like surfactants by adding appropriate organic salts into conventional surfactants is a convenient method to achieve desired properties of surfactant aggregates.
一种具有可变齐聚度的星形齐聚型表面活性剂已由四臂羧酸盐（4EOCOONa）和阳离子单链表面活性剂十二烷基三甲基溴化铵（DTAB）形成。通过表面张力、电导率、等温滴定微量热法、ζ 电位、动态光散射、H NMR 光谱和稳态荧光测量研究了 4EOCOONa/（DTAB）配合物的聚集。量热结果表明，4EOCOONa 与 DTAB 强烈相互作用，每个 4EOCOONa 分子结合六个 DTAB 分子，其中四个 DTAB 分子通过静电相互作用结合到一个 4EOCOONa 分子上，另外两个 DTAB 分子通过疏水相互作用进一步结合到 4EOCOONa/（DTAB）配合物上。4EOCOONa/（DTAB）配合物的临界胶束浓度（CMC）明显低于 DTAB 的 CMC，类似于合成的星形齐聚型表面活性剂。DTAB/4EOCOONa 混合物的胶束性质取决于 4EOCOONa/（DTAB）配合物的组成变化。通过增加 DTAB/4EOCOONa 的摩尔比和/或浓度，DTAB/4EOCOONa 混合物逐渐形成 4EOCOO(DTA)、4EOCOO(DTA)、4EOCOO(DTA)、4EOCOO(DTA)和 4EOCOO(DTA)的配合物，相应的聚集物是具有松散分子堆积的小阴离子胶束，以及具有更紧密堆积的近乎非离子或带正电的小胶束。此外，随着浓度和 DTAB/4EOCOONa 摩尔比的增加，小胶束的正电荷增加。因此，通过向常规表面活性剂中添加适当的无机盐来构建齐聚型表面活性剂是实现所需表面活性剂聚集物性能的一种简便方法。
