ABSTRACT
The interaction between poly(diallyldimethylammonium chloride) (PDADMAC) and ionic surfactant sodium decyl sulfate (C(10)SO(4)Na) in aqueous solution was investigated by means of dielectric relaxation spectroscopy. To better understand the interaction, the dielectric behaviors of PDADMAC solution and C(10)SO(4)Na 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(10)SO(4)Na solution, dielectric relaxation was observed at submicellar concentrations, which is ascribed to the counterion diffusion around premicelles. For the aqueous solutions of a PDADMAC/C(10)SO(4)Na mixture with different C(10)SO(4)Na 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 C(10)SO(4)Na solution. The possible interaction pattern and microstructure of the PDADMAC/C(10)SO(4)Na complex were proposed on the basis of the dielectric behavior.
ABSTRACT
Dielectric measurements were carried out on aqueous solution of poly(diallyldimethylammonium chloride) (PDADMAC) with different concentrations at room temperature. Additionally, for selected solutions the temperature dependence of dielectric relaxation spectroscopy (DRS) was examined in the range of 5-70 degrees C. The dielectric relaxation in the order of around MHz was observed, and the dielectric parameters were determined from the dielectric spectra by fitting data with the Cole-Cole equation. The dielectric parameters showed strong dependences on concentration and on temperature, respectively, and these dependences are analyzed by the scaling theory. From the analysis of concentration dependence of dielectric parameters, the dielectric relaxation is assigned to the localized fluctuation of uncondensed counter-ions over the distance between chains in dilute solution and correlation length in semi-dilute solution, respectively, and the solvent quality parameter for the uncharged polyelectrolyte chain is evaluated. By the analysis of temperature dependence of dielectric parameters, we find that: the physical meanings of the typical lengths of uncondensed counter-ions are not influenced by temperature; in semi-dilute solution, the highly extended length of the chain (correlation length) increases and the end-to-end distance of the chain decreases with increasing solution temperature; in the change process of dielectric relaxation of PDADMAC solution induced by the increase of temperature, the increment of ionic diffusion coefficient and decrement of permittivity of the solvent medium are the major factors. The enthalpy and entropy of activation of the dielectric relaxation are experimentally determined by the dependence of relaxation time on temperature, individually.
ABSTRACT
Dielectric measurements were carried out on colloidal suspensions of palladium nanoparticle chains dispersed in poly(vinyl pyrrolidone)/ethylene glycol (PVP/EG) solution with different particle volume fractions, and dielectric relaxation with relaxation time distribution and small relaxation amplitude was observed in the frequency range from 10(5) to 10(7) Hz. By means of the method based on logarithmic derivative of the dielectric constant and a numerical Kramers-Kronig transform method, two dielectric relaxations were confirmed and dielectric parameters were determined from the dielectric spectra. The dielectric parameters showed a strong dependence on the volume fraction of palladium nanoparticle chain. Through analyzing limiting conductivity at low frequency, the authors found the conductance percolation phenomenon of the suspensions, and the threshold volume fraction is about 0.18. It was concluded from analyzing the dielectric parameters that the high frequency dielectric relaxation results from interfacial polarization and the low frequency dielectric relaxation is a consequence of counterion polarization. They also found that the dispersion state of the palladium nanoparticle chain in PVP/EG solution is dependent on the particle volume fraction, and this may shed some light on a better application of this kind of materials.
ABSTRACT
Dielectric relaxation spectra of tetrabutylammonium perfluorooctanoate (TBPFO), an anionic fluorocarbon surfactant with two cloud points in aqueous solution, were investigated in the frequency range from 40 Hz to 110 MHz. Striking dielectric relaxations were observed when both the temperature-dependent and concentration-dependent phase transitions in TBPFO aqueous solution occurred. The changes in dielectric relaxation and the distribution of dielectric parameters were consistent with the phase boundaries of the phase diagram. In the first homogeneous phase region, two relaxations of rodlike micelles appeared at about 100 kHz and 5 MHz, which originated from the diffusion of the free counterions in the directions of the long axis and the short axis of rodlike micelles, respectively. With increasing temperature, two relaxations gradually turned to one as a result of the formation of connected or entanglement points between the wormlike micelles. The lengths of the long half-axis and the short half-axis of the rodlike micelles, as well as the average distance of the connected or entanglement points of the wormlike micelles, were evaluated by the obtained relaxation times.
ABSTRACT
Dielectric measurements were carried out for suspensions of D354 anion-exchange beads dispersed in electrolyte solutions at different concentrations, and distinct Maxwell-Wagner dielectric relaxations were observed around 10(6) Hz. Through fitting the experimental data we obtained the dielectric parameters of the suspensions, and then we calculated the phase parameters from the dielectric parameters and the measured volume fractions by Hanai's method. In light of the present understanding of the interfacial properties, and with the information obtained from the phase parameters, we satisfactorily interpreted the concentration dependences of the dielectric parameters. It is concluded that Hanai's method is an effective tool for obtaining the properties of dispersed particles; the properties of the electrical double layer, which are mainly decided by the properties of the electrolyte solution, predict the dielectric behavior of suspensions with conducting particles. The dielectric relaxation spectroscopy (DRS), based on the M-W mechanism, is also a very sensitive tool for probing the properties of the liquid/solid interface.
ABSTRACT
The phenomenon of two dilute aqueous phases composed of sodium dodecylsulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) was investigated under various conditions such as concentrations and molar ratios of the two surfactants, the addition of sodium chloride and temperature. Vesicles formation was found in the both phases by TEM image.
