支链醇对Gemini表面活性剂表面活性和胶束化行为的影响

Effects of Branched-Chain Alcohols on Surface Activity and Micellization of Gemini Surfactants

Gemini表面活性剂是一类高效的新型表面活性剂,而醇是工业界和日化领域最常采用的表面活性剂助剂,因此研究不同结构的醇对Gemini表面活性剂表面活性和胶束化行为的影响规律和机理对于促进Gemini表面活性剂的发展和实际应用具有重要意义.利用表面张力、电导、等温滴定微量热,低温透射电镜和核磁共振研究了直链醇1-戊醇和具有相同主链的支链醇2-己醇与3-庚醇对具有不同长度连接基团阳离子季铵盐型Gemini表面活性剂C12CSC12Br2(S=2,4,6,8,10,12)的表面活性和胶束化行为的影响,结果发现,支链醇能够显著影响表面活性剂在气/液界面的排布,使得C20(使溶剂的表面张力降低20 mN/m所需的表面活性剂浓度)和γCMC(CMC时表面张力值)随醇支化度的增加而显著降低,而支链醇对表面活性剂在溶液中的临界胶束浓度以及胶束的尺寸和形貌均没有明显影响,同时这些醇对Gemini表面活性剂的影响与连接基团的长度相关.阐述了上述结果产生的机理,将有助于指导如何选择合适结构的醇助剂去调控Gemini表面活性剂的表面和溶液性质.

Gemini surfactants are a kind of novel and efficient surfactants and alcohols are one of the most widely used additives to surfactant products in industries and daily life. Understanding the effects of alcohols on surface activities and micellization of gemini surfactants will promote the applications of gemini surfactants. Effects of linear-chain alcohol(1-pentanol) and branched-chain alcohols(2-hexanol and 3-heptanol) with the same main chain as 1-pentanol on the surface activity and micellization of cationic ammonium gemini surfactants C12CSC12Br2(S=2, 4, 6, 8, 10, 12) in aqueous solution have been investigated by surface tension, electrical conductivity, isothermal titration microcalorimetry(ITC), cryogenic transmission electron microscopy(Cryo-TEM), and NMR techniques. The branched-chain alcohols have not shown obvious effects on the critical micelle concentration of surfactants(CMC), the size and the morphology of micelles due to loose microstructure and weak interactions between the alcohols and the gemini surfactant molecules. However, the addition of branched-chain alcohols greatly decreases the surface tension of surfactants and the surface tension decreases with the increase of the branching factor of the alcohols. In addition, the surfactant concentration required to reduce the surface tension of the solvent by 20 mN/m(C20) and the surface tension values of the surfactants at CMC(γCMC) decrease obviously with the increment of the branching factor of the alcohols at a fixed alcohol concentration due to the increase of the hydrophobic chain density at the air/solution interface. The results suggest that the branched-chain alcohols influence the self-assembly of surfactants more obviously at the air/solution interface than in micelles. Moreover, there is a second critical concentration in the surface tension curves of C12C10C12Br2 and C12C12C12Br2 with a longer spacer, indicating that the hydrophobic chains of these gemini surfactants are not packed tightly even above CMC due to the flexibility of their spacers and low CMC, and are packed more tightly with the increase of the surfactant concentration. The addition of alcohols decreases the second critical concentration remarkably with the increase of their branching factor, which means that the branched alcohols have a more obvious effect on the surface activity of gemini surfactants with a longer spacer. This work helps us to understand the effects of branched-chain alcohols on the self-assembly of gemini surfactants at air/solution interface and in bulk solution, and may provide some guidance on how to choose alcohols to adjust surface activities and micellization of gemini surfactants.