Chen Ji, Hu Xue-Yi, Fang Yun, Jin Guang-Yong, Xia Yong-Mei
Key Laboratory of Synthetic and Biological Colloids (Ministry of Education), School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, PR China.
Key Laboratory of Synthetic and Biological Colloids (Ministry of Education), School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, PR China.
J Colloid Interface Sci. 2019 Jul 1;547:190-198. doi: 10.1016/j.jcis.2019.04.002. Epub 2019 Apr 2.
The properties of conventional surfactants (c-surfactants) are generally accepted to be amphipathicity-dominated, but extended surfactants (e-surfactants) are additionally polypropylene oxide (PPO)-dependent; this additional property makes us wonder how an intramolecular PPO spacer would be "extended" at various interfaces and what is responsible for the excellent all-round properties of e-surfactants.
A series of novel sodium medium alkyl chain PPO-b-PEO sulfates (2-ethylhexyl polypropylene oxide-block-polyethylene oxide sulfates, CPES) were designed, synthesized and structurally identified. Tensiometry was applied to estimate the surfactant shape at the air/water surface. Surface tension, interfacial tension, emulsifying power, electrolyte tolerance, adsorption onto oil sands and thermal hydrolysis stability were measured to evaluate the effect of the PPO coil on the interfacial and micellar properties of the e-surfactants.
On the basis of obtaining greater values for e-surfactants than c-surfactants for both surface area (a) per surfactant molecule and the corresponding shape factor (S), we were surprised to find that e-surfactants form a rugby ball shape not only at the air/water surface but also at the oil/water interface; this result is potentially explained by the PPO spacer coiling and collapsing to produce dense packing at the monolayer adsorption, which is rationally borrowed by other interfaces. Many positive or negative correlations were observed between the interfacial/micellar properties of CPES and a values, which seems that the surfactant shape dominants the properties of the e-surfactants. In fact, the properties of CPES are dominated by the dynamic amphipathicity and assisted by the rugby ball shape of the molecules because of both being driven by the dynamic biphasic affinity of the PPO coil in response to the external environment; these findings provide soft interfacial materials specially adapted for surfactant flooding.
传统表面活性剂（c - 表面活性剂）的性质通常被认为是以两亲性为主导，但扩展表面活性剂（e - 表面活性剂）还额外依赖于聚环氧丙烷（PPO）；这种额外的性质使我们想知道分子内的PPO间隔基在各种界面处会如何“扩展”，以及是什么赋予了e - 表面活性剂出色的综合性能。
设计、合成并对一系列新型中链烷基钠PPO - b - PEO硫酸盐（2 - 乙基己基聚环氧丙烷 - 嵌段 - 聚环氧乙烷硫酸盐，CPES）进行了结构鉴定。应用张力测量法来估计空气/水表面的表面活性剂形状。测量了表面张力、界面张力、乳化能力、耐电解质能力、在油砂上的吸附以及热水解稳定性，以评估PPO链对e - 表面活性剂界面和胶束性质的影响。
基于e - 表面活性剂的每个表面活性剂分子的表面积（a）和相应的形状因子（S）都比c - 表面活性剂的值更大，我们惊讶地发现e - 表面活性剂不仅在空气/水表面而且在油/水界面都形成橄榄球形状；这一结果可能是由于PPO间隔基盘绕和折叠，在单层吸附时产生紧密堆积，而其他界面也合理地借鉴了这种堆积方式。在CPES的界面/胶束性质与a值之间观察到许多正相关或负相关，这似乎表明表面活性剂形状主导了e - 表面活性剂的性质。实际上，CPES的性质由动态两亲性主导，并由分子的橄榄球形状辅助，因为两者都是由PPO链响应外部环境的动态双相亲和力驱动的；这些发现提供了特别适用于表面活性剂驱油的软界面材料。
