3 research outputs found

    Interaction and Dynamics of Associated Formamide in TX100–Formamide Binary Mixtures by Dielectric Spectroscopy

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    Dielectric behaviors of a binary mixture composed of TX100 (a nonionic surfactant) and formamide (FA) at different surfactant concentrations and varying temperature were investigated over a frequency range from 40 Hz to 110 MHz. One relaxation appeared around gigahertz is considered to be from the contribution of two types of FA; one is “free FA”, which has no interaction with surfactant, and the other is “associated FA”, which can interact with surfactant. Conductivity was used to determine the number of associated FAs, and the result indicates that each ethylene oxide (EO) segment binds to one FA molecule. The dipole moment of the associated FA was calculated by using Cavell equation, and it is smaller than those of bulk FA, while the dipole rotation time of associated FA is higher than that of bulk FA. This suggests that the dynamics of associated FA is restricted by the hydrophilic chain of surfactant. The thermodynamic parameters, obtained from the temperature dependences of the relaxation times, revealed that in dilute TX100–FA solution the interaction of FA with EO segment of surfactant is weaker compared with the FA–FA hydrogen bond. This work also demonstrated that the dynamics of associated FA is quite similar to that of hydration water

    Dielectric Analysis for the Spherical and Rodlike Micelle Aggregates Formed from a Gemini Surfactant: Driving Forces of Micellization and Stability of Micelles

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    The self-aggregation behavior of Gemini surfactant 12-2-12 (ethanediyl-1,2-bis­(dimethyldodecylammonium bromide)) in water was investigated by dielectric relaxation spectroscopy (DRS) over a frequency range from 40 Hz to 110 MHz. Dielectric determination shows that well-defined spherical micelles formed when the concentration of the surfactant was above a critical micelle concentration CMC<sub>1</sub> of 3 mM and rodlike micelles formed above CMC<sub>2</sub>, 16 mM. The formation mechanism of the spherical micelles and their transition mechanism to clubbed micelles were proposed by calculating the degree of counterion binding of the micelles. The interactions between the head groups and the hydrophobic chains of the surfactant led to the formation of the micelles, whereas the transition is mainly attributed to the interaction among the hydrophobic chains. By analyzing the dielectric relaxation observed at about 10<sup>7</sup> Hz based on the interface polarization theory, the permittivity and conductivity of micelle aggregates (spherical and clubbed) and volume fraction of micelles were calculated theoretically as well as the electrical properties of the solution medium. Furthermore, we also calculated the electrokinetic parameters of the micelle particle surface, surface conductivity, surface charge density, and zeta potential, using the relaxation parameters and phase parameters. On the basis of these results, the balance of forces controlling morphological transitions, interfacial electrokinetic properties, and the stability of the micelle aggregates was discussed

    Dielectric Insights into the Microcosmic Behavior of Ionic Liquid-Based Self-Assemblyî—¸Microemulsions/Micelles

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    Dielectric relaxation spectra of ([Bmim]­[BF<sub>4</sub>]/TX-100/<i>p</i>-xylene) microemulsions and ([Bmim]­[BF<sub>4</sub>]/TX-100) micelles were measured. A specific dielectric relaxation changing with the concentration of ionic liquids (ILs) was observed in the range of 10<sup>6</sup>–10<sup>8</sup> Hz. When dielectric parameters were combined with the Einstein displacement equation and Bruggeman’s effective-medium approximation, the interaction between [Bmim]­[BF<sub>4</sub>] and <i>p</i>-(1,1,3,3-tetramethylbutyl) phenoxypolyoxyethyleneglycol (TX-100) in microemulsions/micelles was presented: because of the electrostatic interaction and van der Waals force, [Bmim]­[BF<sub>4</sub>] is bound around the polyethylene oxide (PEO) chains of TX-100, and once the electric field is added, ions of [Bmim]­[BF<sub>4</sub>] will move along the PEO chain. The dependence of dielectric and phase parameters such as relaxation time, permittivity, and volume fraction on the mass fraction of ILs presents an evidence for our proposals about the transition of both systems with the increase of IL content. In addition, it was confirmed that percolation is a unique phenomenon in microemulsions and the percolation mechanism here belongs to static percolation. The transition process of micelles with the change of IL content is presented from the dielectric view
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