title: Properties of polyethylene glycol (23) lauryl ether with cetyltrimethylammonium bromide in mixed aqueous solutions studied by self-diffusion coefficient NMR.
abstract: NMR self-diffusion coefficient measurements have been used to study the properties of polyethylene glycol (23) lauryl ether (Brij-35) with cetyltrimethylammonium bromide (CTAB) in the mixed aqueous solutions with different mole fractions of CTAB. By fitting the self-diffusion coefficients to the two-state exchange model, the critical micelle concentrations of the two solutes in the mixed solutions (cmc*1 and cmc*2) were obtained. The critical mixed micelle concentrations (cmc*) were then evaluated by the sum of cmc*1 and cmc*2, which are in good agreement with the results measured by the surface tension method. The cmc* values are lower than those of the ideal case of mixing, which indicates that the behavior of the CTAB/Brij-35 system is nonideal. Moderate interactions between CTAB and Brij-35 in their mixtures can be deduced from the interaction parameters (betaM) based on the cmc* obtained by the NMR self-diffusion method. The compositions (x1) of the mixed micelles at different total surfactant concentrations were also evaluated. By using these results, a possible mechanism of mixed micellar formation and a picture of the formation of nonsimultaneous CTAB/Brij-35 binary mixed micelle were proposed. In contrast to the case of CTAB/TX-100 system, Brij-35 molecules have a tendency to form micelles first at any mole fraction of CTAB. The mixed micellar self-diffusion coefficients (Dm) increase slightly at lower CTAB molar ratios, and then speed up with increasing CTAB mole fraction.
authors.affiliation: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China.
authors.forename: HongChang
authors.initials: H
authors.lastname: Gao
authors.forename: RongXian
authors.initials: R
authors.lastname: Zhu
authors.forename: XiaoYan
authors.initials: X
authors.lastname: Yang
authors.forename: ShiZhen
authors.initials: S
authors.lastname: Mao
authors.forename: Sui
authors.initials: S
authors.lastname: Zhao
authors.forename: JiaYong
authors.initials: J
authors.lastname: Yu
authors.forename: YouRu
authors.initials: Y
authors.lastname: Du