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Zhou H.-T.,China University of Petroleum - East China | Lin S.-S.,CAS Beijing National Laboratory for Molecular | Xing H.,Beijing FLUOBON Surfactant Institute | Gao A.-T.,Beijing Institute of Technology | Xiao J.-X.,Beijing FLUOBON Surfactant Institute
Colloids and Surfaces A: Physicochemical and Engineering Aspects

The effects of different concentrations of sodium thiocyanate (NaSCN) on the homogeneous solution of equimolarly mixed decyltriethylammonium bromide and sodium decylsulfonate (C10NE-C10SO3) were studied by 1H NMR, surface tension and dynamic light scattering (DLS) measurements. For the system of C10NE-C10SO3, the NMR signals were greatly broadened in the micellar concentration region. However, the shape of the NMR peaks for the micellar solutions of C10NE-C10SO3, especially for those protons adjacent to headgroups, recovered to be fine-resolved with the gradual increase of NaSCN concentration. Therefore, the NMR method directly evidenced that the electrostatic attraction between the oppositely charged headgroups in the micellar solution of C10NE-C10SO3 was significantly reduced by NaSCN. The surface tension results showed that both the surface tension at critical micelle concentration (γcmc) and the minimum molecular area in the surface adsorbed layer (Amin) were remarkably increased when NaSCN was added to C10NE-C10SO3. As shown by DLS, the addition of NaSCN could significantly induce the decrease of the aggregate size of C10NE-C10SO3. Both surface tension and DLS results supported the conclusions made by NMR. © 2012 Elsevier B.V. Source

Zhao K.-S.,Beijing Normal University | Jia Z.-J.,Beijing Normal University | Yang L.-K.,Beijing Normal University | Xiao J.-X.,Beijing FLUOBON Surfactant Institute
Chemical Research in Chinese Universities

The dielectric spectra of aerosol OT[AOT, sodium(bis-2-ethylhexyl)sulfosuccinate]/water systems at different concentrations and temperatures were investigated by the dielectric relaxation spectroscopy(DRS). Through the dielectric spectra of different concentrations, two dielectric relaxations were observed over a frequency range from 40 Hz to 110 MHz and the mechanisms of the relaxations were also interpreted based on the Grosse's model. The low-frequency relaxation(around 105 Hz) was attributed to the radial diffusion of counterions along the long-half axis of the rod-like micelle, and the high-frequency relaxation(around 106 Hz) was ascribed to the radial diffusion of counterions along the short-half axis. Furthermore, specific emphasis was placed on studying the effects of temperature on system's conductivity. It was observed that the low-frequency limit of conductivity(?l) decreased and then increased with the increment of temperature under the measured concentration. On the other hand, the conductivity(?m and ?h) in meso- and high-frequency ranges always increased as temperature increased. Both the tendencies of alteration which mentioned above should be related to the phase transition of AOT/water system. Source

Chen Z.,Beijing Normal University | Li X.-W.,Beijing Normal University | Zhao K.-S.,Beijing Normal University | Xiao J.-X.,Beijing FLUOBON Surfactant Institute | Yang L.-K.,Beijing Normal University
Journal of Physical Chemistry B

The interaction between poly(diallyldimethylammonium chloride) (PDADMAC) and ionic surfactant sodium decyl sulfate (C10SO4Na) in aqueous solution was investigated by means of dielectric relaxation spectroscopy. To better understand the interaction, the dielectric behaviors of PDADMAC solution and C10SO4Na solution were also separately studied. For PDADMAC solution, two relaxations were observed, which were attributed to the polarization of loosely bound counterions along the directions parallel and perpendicular to the PDADMAC chain. For C 10SO4Na solution, dielectric relaxation was observed at submicellar concentrations, which is ascribed to the counterion diffusion around premicelles. For the aqueous solutions of a PDADMAC/C10SO 4Na mixture with different C10SO4Na concentrations, three surfactant concentration regions characterized by different dielectric behaviors were observed. The dielectric behavior in different regions was discussed through comparing it with that of PDADMAC solution and C10SO4Na solution. The possible interaction pattern and microstructure of the PDADMAC/C10SO4Na complex were proposed on the basis of the dielectric behavior. © 2011 American Chemical Society. Source

Xing H.,CAS Beijing National Laboratory for Molecular | Xing H.,Beijing FLUOBON Surfactant Institute | Zhou H.-T.,China University of Petroleum - East China | Yu H.-Q.,Beijing FLUOBON Surfactant Institute | And 3 more authors.
Journal of Chemical and Engineering Data

It is generally considered that complexes of cyclodextrins (CDs) with ordinary surfactants are not surface-active in water. In this work, aqueous mixtures of α-CD, octyltriethylammonium bromide (OTEAB), and sodium perfluorooctanoate (SPFO) were studied by surface tension measurements. Comparison of the experimental results and the simulated ones in the premicellar region showed that the ability of the α-CD/OTEAB complexes to participate in the surface-adsorbed layer was dependent on the overall net charge of the surfactants: for the excess-SPFO system, the α-CD/OTEAB complexes did show a significant contribution to the surface activity of the mixture, but in the system with excess OTEAB, the α-CD/OTEAB complexes were not observed to influence the surface-adsorbed layer. We speculated that the surface-adsorbed layer in the premicellar region might also prefer an electroneutral state, as those cationic-anionic micelles did, and that the α-CD/OTEAB complexes were driven to the surface by electrostatic attractions from the excess oppositely charged SPFO. The calculated results for the surface area per molecule adsorbed at the air-water interface also supported our conclusion. © 2011 American Chemical Society. Source

Xing H.,CAS Beijing National Laboratory for Molecular | Xing H.,Beijing FLUOBON Surfactant Institute | Yan P.,CAS Beijing National Laboratory for Molecular | Zhao K.-S.,Beijing Normal University | And 2 more authors.
Journal of Chemical and Engineering Data

The micellization of dodecyltrimethyl/ethyl/propyl/butylammonium bromide (C12NM, C12NE, C12NP, and C12NB) was investigated by electrical conductivity measurements at different temperatures T. In the investigated temperature range, (15 to 45) °C, both the critical micelle concentration (cmc) and the degree of counterion association (β) decreased with the increase of headgroup size. The cmc as a function of T showed a typical U-shaped relationship. The temperature of the minimum of U-shaped curve (Tmin) increased with the incremental chain length in the headgroups, which was the reverse to the previous results for quaternary ammonium surfactants that Tmin decreased with the increment in the hydrophobic tails. The β approximately exhibited a linear decrease with raising T. Nonlinearity was observed both in ln(cmc) versus Nc and in ΔmicG° versus T, where Nc was the carbon number in the headgroups and ΔmicG° was the standard Gibbs energy of micellization. C12NM and C12NE resembled each other in the thermodynamics of micellization, but they behaved considerably differently from either C12NP or C12NB in the dependence of ln(cmc) on Nc, in the decreasing rate of ΔmicG° versus T, and in the variation of thermodynamic properties with T. All of the surfactants exhibited the enthalpy-entropy compensation phenomenon. The large value of standard entropy of micellization (ΔmicS°) of C 12NB compared with the others could be attributed to the strong hydrophobicity of the tributyl headgroup. © 2010 American Chemical Society. Source

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