Surface Properties And Micellization Behavior Of Mixures Of N-Dodecly-β-D-Maltoside

The surface chemical properties and micellization behavior of anionic/nonionic binary surfactant mixtures have been investigated by Clint, Rubingh and Maeda models using surface tension and fluorescence probe methods.Firstly, the alkyl glycoside nonionic surfactant, n-dodecyl-β-D-maltoside(DDM), polyoxyethylene octylphenol ether (TX-100) and polyoxyethylene (20) cetyl alcohol ether (Brij58), both of which the cmcs were similar to DDM, were selected to compose binary surfactant systems combined with anionic surfactant sodium oleate(NaOA), respectively. According to Clint theory,the negative deviations from ideal mixing in cmcs for three mixed systems were calculated. The interaction parameters (β) obtained for all mixed systems were negative. The β values of DDM/NaOA, TX-100/NaOA and Brij58/NaOA systems reached the lowest point corresponding to molar fractions of NaOA0.4,0.1and0.1, respectively, in which the strongest synergistic effect existed between the two components of the three mixed systems, respectively. The mixing free energy (△GM) was negative and increased gradually with the growth of molar fractions of NaOA, indicating that nonionic components could benefit mixed micelles formation more than ionic components. The results from fluorescence measurement show that the micellar aggregation numbers of anionic/nonionic mixed systems are determined by a delicate balance of two opposite contribution:the electrostatic repulsions between the head groups of the ionic surfactant, and steric interactions of the nonionic surfactant. The variations of micropolarity in mixed systems suggest that the importance of the role played by various steric interactions and hydration.Secondly, the surface properties and micellization behavior of DDM/NaOA system in water and in20%(V/V) ethylene glycol (EG) aqueous solution were investigated, respectively. The hydrophobic interactions between the hydrocarbon chains of DDM were decreased and cmc values of DDM were increased with the adding of EG. Consequently, cmc values of DDM/NaOA were increased with the adding of EG, and the adsorption efficiency of surfactant was reduced. The interaction parameters were negative, indicating that synergistic effect is strongest in mixed systems at αNaOA=0.4. The results from fluorescence measurement indicate that for DDM/NaOA mixed system, the aggregation numbers in water are obviously larger than those in20%EG aqueous solution. I3/I1ratio for DDM/NaOA system in EG aqueous solution was higher than that for DDM/NaOA system in water, indicating that EG can destroy the micellar structure, reduce the micellar aggregation numbers and increase microenvironment polarity. Zeta potential measurements showed that|ζ|values of Zeta potential for mixtures in water were larger than those for mixtures in20%EG aqueous solution, indicating that EG has side effect on micellar stability and enhance the diameter of micelle.Finally, the synergism and micellar properties of binary surfactant mixtures containing anionic surfactants viz. sodium dodecyl sulphate (SDS)and magnesium dodecyl sulphate (Mg(DS)2) and nonionic surfactants viz. n-dodecyl-β-D-maltoside (DDM) and dodecyl tetraethylene glycol ether (Brij30) in aqueous solution were investigated, respectively. And we studied the effects on synergism and micellization from anionic surfactant containing different counter-ions and nonionic surfactant with different head group structures, respectively. The β values of DDM(Brij30)/MDS were negative. Such results indicate that all the mixed systems have strong synergistic effect between the two components of micelles. Results from activity coefficient calculation showed that the Na+and Mg2+have impact on DDM/MDS and Brij30/MDS mixtures. The results of the interaction between surfactants and the contribution of free energy by Maeda’s model were consistent with those from Rubingh’s theory. Moreover, because of nonionic surfactant with more flexible head group, it can encourage the formation of the mixed micelles and counter ions have fewer impact on micellar aggregation numbers and micropolarity of mixed surfactant systems.