title: pH-Regulated surface property and pH-reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution.
abstract: A series of tertiary amide-based gemini surfactants, 2,2'-(1,4-phenylenebis(oxy))bis(N-(3-(dimethylamino)propyl)alkylamide), abbreviated as Cm-A-Cm (m = 8; 10; 12; 14), were synthesized. The surface property and aggregation behaviors of the Cm-A-Cm aqueous solutions were studied in detail. The Cm-A-Cm exhibited high and pH-regulated surface activity at the air/water interface; i.e., the critical micelle concentration was 5.6 × 10(-6) mol L(-1) at pH = 2.50 when m = 14 and was further regulated to 1.8 × 10(-6) mol L(-1) by altering the pH to 6.50. When the pH was tuned from 2.0 to 12.0, the appearance of the C12-A-C12 aqueous solution (35 mM) underwent 5 states: transparent water-like solution, viscous fluid, gel-like fluid, turbid liquid and dispersion system with white precipitate. The results of rheology, cryogenic transmission electron microscopy, and dynamic light scattering characterization revealed that the transition from water-like to viscous or gel-like liquid was actually due to aggregate microstructure transition from spherical to worm-like micelles. This transition was completely reversible between pH = 2.50 and 6.81, tuned by adding HCl and NaOH solutions for at least 4 cycles. Similar micellar transitions regulated by pH were also found for m = 8 and 10, whereas only worm-like micelles were formed for m = 14 at both acidic and nearly neutral conditions. Finally, a reasonable mechanism of aggregate behavior transition was proposed from the viewpoint of the molecular states, molecular structures, and the intra- and inter-molecular interactions.
authors.affiliation: College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China. bgwang@swpu.edu.cn and Engineering Research Center of Oilfield Chemistry, Ministry of Education, Chengdu 610500, P. R. China.
authors.forename: Hongsheng
authors.initials: H
authors.lastname: Lu
authors.affiliation: College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China. bgwang@swpu.edu.cn.
authors.forename: Miao
authors.initials: M
authors.lastname: Xue
authors.affiliation: College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China. bgwang@swpu.edu.cn and Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, Chengdu 610500, P. R. China.
authors.forename: Baogang
authors.initials: B
authors.lastname: Wang
authors.affiliation: College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China. bgwang@swpu.edu.cn and Engineering Research Center of Oilfield Chemistry, Ministry of Education, Chengdu 610500, P. R. China.
authors.forename: Zhiyu
authors.initials: Z
authors.lastname: Huang