The Preparation Of Gemini Surfactants And The Research Of Their Properties

Gemini surfactants are made up of two identical amphiphilic moities covalently connected at the level of the headgroups by a spacer group. By this way the separation between the polar headgroups within Gemini surfactants is strongly decreased when they aggregate and thus the surface activity is greatly enhanced. Compared with conventional surfactants, Gemini surfactants are not only a breakthrought in concept but also are of novel properties. Therefore, Gemini surfactants are reputed as a new generation of surfactant by Rosen. Owing to this, studies on the novel surfactants have attracted considerable attention in surface chemistry domain. In this paper, we react α-brominated methyl dodecanoate with diphenols as the coupling agent via Williamson synthesis of ether, finally a series of carboxylate Gemini surfactants are obtained by saponification. 1,3-Dibromo-2-propanol was prepared from Glycerin, and bis-quaternary ammonium salt which has –OH in the connecting group was obtained from 1,3-Dibromo-2-propanol and dodecyldimethylamine. In this paper, we synthesized two kinds of new carboxylate Gemini surfactants and one of new bis-quaternary ammonium salt. All products are characterized by elementary analysis, IR spectra and 1H-NMR spectra. Surface tension of carboxylate Gemini surfactants was measured by Du-Nouy method in pH=12 NaOH aqueous solution at 30℃. Some fundamental data of these surfactants such as critical micelle concentrations (cmc), surface tension of aqueous solution at cmc (γ_cmc) were determined, and the Γ_max, Amin, pC₂₀ , cmc/C₂₀ were calc-ulated. The result indicated that they have high surface activity. Especially, the sodium carboxylate Gemini surfactant containing p-biphendioxy spacer has small A_min and big Γ_max.This may itself reflect multiplayer formation. Because of the limitation of experiment condition, the phenomenon will be researched in the future. The intrinsic fluorescence quenching of carboxylic sodium Gemini surfactants in aqueous solution by methylviologen(MV2+) was investigated. It was found that the relationship, ln(I0/I)=N, is applicable to the process and the average micelle aggregation number(N) of them in pH=12 NaOH aqueous solution at 30 oC can be calculated. The N is 3a>3b>3c . Adsorption kinetics of Gemini surfactant (C12N)2OH at the water-air interface was studied by maximum bubble pressure technique. The kinetics effect of adsorption was enhanced when the bulk concentration, electrolyte concentration or the temperature was increased because the surfactant molecules moved faster from the bulk to the surface. Compared with the conventional surfactantDTAB,C12-(CH2)3-C12 which had the same kind of head group and the same length of hydrophobic chain as (C12N)2OH, the latter seemed more favorable to adsorb at the surface than the former. Our calculation show that the adsorption barrier of (C12N)2OH is 15.9kJ.mol-1(in the 0.31mmol.L-1 aqueous solution).