Research status and prospect of Gemini surfactant/polymer interactions

Abstract

Gemini surfactants are constructed by two hydrophobic chains and two polar/ionic head groups covalently connected by a spacer group at the level of or in close vicinity to the head groups. Due to their special self-assembly ability, they are superior to the corresponding conventional monomeric surfactants in characteristic features, such as remarkably low critical micellar concentration (CMC), high surface activity, unusual rheological properties, multifarious aggregate structures, better wetting ability, and so on. Owing to these unique properties, gemini surfactants have shown great promise in various areas. Gemini surfactants have been attracting great attention in both the academic and industrial worlds. There is increasing pressure to reduce our dependency on resources and to reduce the load we place on the environment. Surfactant-based formulations for water purification pharmaceuticals, cosmetics, detergency and oil recovery normally contain water-soluble polymers. Surfactant/polymer mixtures can provide improved properties that neither the surfactant nor the polymer has when present alone. Greater efficiency in these mixture systems would both reduce consumption and decrease pollution. The unusual efficiency and versatility of gemini surfactants offer the possibility of developing much more efficient and functional surfactant/polymer systems. Therefore, the interactions between gemini surfactants and polymers (containing polyelectrolytes, nonionic polymers, and hydrophobically modified polymers) have attracted considerable attention. It is important to systematically characterize the interactions between gemini surfactants and polymers, which can offer effective guidance to design the surfactant/polymer mixtures with desired properties by using such highly efficient surfactants. Here, we summarize the systems investigated in our laboratory, combined with the studies from other researchers, to give a comprehensive review on research progress of gemini surfactant/polymer interactions. This review will include the following three parts, (1) interaction between the cationic gemini surfactants m - s - m and polyelectrolytes, nonionic polymer, and hydrophobic modified polymer; (2) interaction between the special gemini surfactant and different polymers; (3) conclusion and prospect. Although the research of gemini surfactants/polymer interactions have made some progress, the more systematic studies still be needed due to the continuous innovation and development of gemini surfactant structure. In order to further to improve the efficiency of the gemini surfactant, a kind of novel oligomeric surfactants have been developed in the recent years. As compared with the gemini surfactants, the oligomeric surfactants have the more hydrophilic headgroups and hydrophobic alkyl chains, and the more complex molecular configuration. From the existing reports, it is found that the oligomeric surfactants have the very strong aggregation ability and very low critical micelle concentration. Some oligomeric surfactants can form the large aggregates by the strong intermolecular hydrophobic interaction at very low concentrations (only several micromoles), which will greatly improve the surfactant efficiency. At present, the studies on the oligomeric surfactant/polymer interaction are very scarce. For both gemini and oligomeric surfactant, the main reasons to limit their large-scale application are the difficult synthesis and high cost of these surfactants. In order to solve these problem, the constructed gemini and oligomeric surfactants by the non-covalent interactions have been developed in recent years. By mixing the conventional surfactants with special structure of organic acid or salt, we have successfully constructed many kinds of gemini and oligomeric surfactants, and these surfactants exhibited the similar aggregation behaviour just like the synthesized surfactants. The systematic studies on the interaction between the constructed gemini or oligomeric surfactants with the different polymer are also needed. With the deeply understanding to the gemini surfactant/polymer interaction, the researchers will gradually optimize the properties and functions of surfactant/polymer complex system, and strive for the realization of the large-scale application of gemini surfactants in the industrial fields.