3 research outputs found
Interaction and Dynamics of Associated Formamide in TX100–Formamide Binary Mixtures by Dielectric Spectroscopy
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
The
self-aggregation behavior of Gemini surfactant 12-2-12 (ethanediyl-1,2-bisÂ(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
Dielectric relaxation
spectra of ([Bmim]Â[BF<sub>4</sub>]/TX-100/<i>p</i>-xylene)
microemulsions and ([Bmim]Â[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]Â[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]Â[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]Â[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