Aggregation Behavior of Ethoxylated Phytosterol Surfactants in Different Protic Solvents: An Insight from Dielectric Relaxation Studies.

The micellar aggregation behavior of biocompatible surfactants, phytosterol ethoxylates (BPS-n, n is the oxyethylene (EO) chain length), containing polyoxyethylene chains in four organic solvents (glycerol (G), ethylene glycol (EG), formamide (FA), and N,N-dimethylformamide (DMF)) was studied by dielectric spectroscopy in the frequency range of 40 Hz to 110 MHz. Only the BPS-n/EG and BPS-n/G systems show distinct dielectric loss peaks near 104 Hz, indicating that BPS-n forms micellar aggregates in EG and G solvents, and the interfacial polarization (IP) between the aggregates and solvents leads to this relaxation. The dielectric spectra were analyzed based on the IP theory and a columnar dispersion model. The dielectric parameters of micelles, the permittivity and conductivity of micelles and solvents, and the volume fraction of the aggregates in solvents were calculated. On this basis, the binding numbers of each EO group on the hydrophobic chain to the solvent molecules EG and G were calculated to be 0.42 and 0.22, respectively. It was suggested that the aggregation appears to be related to the magnitude of the hydrogen bonding interactions. The lower number of EO group-binding solvents is because of the strong steric effect of alcohol solvents and the magnitude of the hydrogen bonding force.

Dielectric Analysis of Microcapsule-Immobilized Composite Capsules Suspension: Substances Release.

Dielectric spectroscopy has unique advantages in monitoring drug release. In this work, a dielectric measurement was carried out on the release of the substances of microcapsule-immobilized composite capsules, which were fabricated by encapsulating the Perinereis aibuhitensis extract-loaded gum Arabic/gelatin microcapsules (PaE: GA/GE-MCs) in calcium alginate hydrogel (PaE: CA/GA/GE-CCs). We established the dielectric model of PaE: CA/GA/GE-CCs and got in-depth information on the systems. There are two relaxations in the dielectric spectroscopy, both of which are caused by interfacial polarization. The relaxation mechanisms correspond to the interfacial polarization of the PaE-loading core/calcium alginate shell interface and the calcium alginate shell/solution interface, respectively. Besides, the swelling of composite capsules and substance migration in the composite capsules were observed by analyzing phase parameters. Finally, the characteristic release of calcium alginate composite capsules was confirmed, and the substance release mechanism of composite capsules, namely, the swelling-diffusion mechanism, was obtained.

Desalination behavior analysis of interior-modified carbon nanotubes doped membrane by dielectric spectrum and molecular simulation.

Carbon nanotube (CNT)-doped polyamide (PA) membranes have attracted much attention in reverse osmosis (RO) membranes due to their significant advantages of water flux and desalination. In this study, we synthesized multi-walled carbon nanotube (MWNT)/PA RO membrane by 12-oxodidodecanoic acid methyl ester group interior-modified MWNTs (MWNT-C14H25O4). Then, their mechanism of desalination behavior was successfully analyzed by combining dielectric relaxation spectrum (DRS) and molecular dynamics (MD) simulation. DRS analysis mainly focuses on two aspects: (1) the water volume fraction, average pore size and dielectric parameters of MWNT-C14H25O4/PA and PA membranes were obtained by model analysis of DRS data. These data of MWNT-C14H25O4/PA membrane are higher than PA membrane, which indicates that the water flux of the MWNT-C14H25O4/PA membrane was higher than that of the PA membrane. (2) Further analysis shows that the MWNT-C14H25O4/PA membranes have high average charge density, ion solvation barrier and reflection coefficient, which indicates that the added interior-modified MWNT can improve the salt rejection of PA membranes. In the microscopic aspect, the desalination behavior of the MWNT-C14H25O4/PA and PA membrane was analyzed from the aspects of free volume distribution, the dynamic diffusion process of water and ions. The results show that the microscopic data of dynamic simulation well support the conclusion of the DRS method. This study provides a convenient methodology to characterize the properties of the membrane from the aspect of membrane structure.

Broadband dielectric properties of honey: effects of temperature.

Dielectric properties of jujube honey were investigated at 298-358 K by broadband dielectric measurements. Four relaxation processes were observed and analyzed, which are caused by long range correlation of density fluctuation, cooperative motions of molecules, rotational polarization of bound water and collective reorientation of free water, respectively. The results of temperature dependence of dielectric parameters show that with increasing temperature, the interaction among the molecules e.g. water, fructose and glucose molecules etc. weaken, and the honey gradually forms a complete sugar solution. At a given temperature, the penetration depth at 27 MHz is much greater than that at 915 MHz and 2.45 GHz. And based on the calculated penetration depth, dielectric heating at 27 MHz seems to has more advantages for large volume of materials.

Dielectric Behavior and Phase Behavior of Block Copolymer PEO13-PPO30-PEO13 Aqueous Solution.

Dielectric spectroscopy can be applied to study the structure and dynamics of block polymer. In this work, dielectric measurements of block copolymer Pluronic L64 solution are carried out in the frequency range between 40 Hz and 110 MHz with variable temperatures and concentrations. We analyze the phase behavior of the PEO13-PPO30-PEO13 (Pluronic L64) aqueous system according to the concentration/temperature-dependence of direct current conductivity. The result indicates the sensitivity of the phase behavior and conductivity of the Pluronic L64 solution to temperature. Besides, two relaxations were observed: relaxation 1 (0.5 MHz) is related to the gelation process, while relaxation 2 (5 MHz) is caused by the interface polarization. On the basis of relaxation 2, the volume fraction and permittivity of the particle were calculated. The formations of the block copolymer micelle and gel are monitored successfully by the temperature/concentration-dependence of the dielectric parameters and the volume fraction.

Effect of grafting density on conformation of poly(acrylic acid) in solution by dielectric spectroscopy.

The effect of grafting density of poly(ethylene oxide) and dodecyl groups on the conformation of poly(acrylic acid) in solution was clarified by dielectric relaxation spectroscopy over a frequency range from 40 Hz to 110 MHz. Two distinct dielectric relaxations were found after the elimination of electrode polarization, and valuable information about the conformations and interfacial electrokinetic properties of molecules was obtained by analyzing the dielectric spectra based on a refined double-layer polarization model. The critical aggregation concentration was determined by the concentration dependency of dielectric parameters. The results based on zeta potential suggested that the ionization performance and behavior of counterion condensation were strongly influenced by the grafting density of poly(ethylene oxide) and dodecyl groups. The concentration dependency of correlation length, ratio of zeta potential, ratio of linear density of counterions, and the Debye length showed that the chain length and degree of intermolecular aggregation were also strongly influenced by the grafting density. We revealed the role of grafting density with respect to electrostatic interaction in determining the chain conformation of polyelectrolytes in solution.

Chain conformation of poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl in solution: an anomalous counter-ions condensation.

A dielectric spectroscopy study on a polyelectrolyte in aqueous solutions, which contains hydrophobic groups in part of the side chains poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl (PAA-g-PEO-g-dodecyl) is reported. A refined double layer polarization model was proposed to analyze the double dielectric relaxations in the dielectric spectra. Various electrical and structural parameters of the copolymers were obtained. Besides the crossover concentration, another turning point around 4 mg mL-1 was identified through the analysis of all the dielectrical parameters including dielectric increment, relaxation time and correlation length. According to the scaling relationship between the correlation length and concentration, a necklace-like structure was predicted. In addition, 4 mg mL-1 was proven to be the transition point between string-controlling with bead-controlling structure of the chains. In addition, the fraction of effective charges on the chains was illustrated by Ito's counter-ions fluctuation theory, as well as its linear dependence relationship with the zeta potential. Meanwhile, the counter-ions condensation behavior was consistent with the avalanche-like trend, which was predicted by theory for a hydrophobic polyelectrolyte with a necklace conformation. The results demonstrated that the electrostatic interactions were the main driving force of the necklace-like structure with pendant globules when the string-controlling structure was below 4 mg mL-1. While hydrophobic interactions are the main driving force of the structure of bead-controlling above 4 mg mL-1.

Relaxations and phase transitions during the collapse of a dense PNIPAM microgel suspension-thorough insight using dielectric spectroscopy.

The dielectric behavior of a thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel suspension with a dense concentration was investigated over the frequency range of 40 Hz to 110 MHz in a wide temperature window of 10-60 °C. By successfully removing the electrode polarization effect from the original data, two remarkable and temperature-dependent relaxation processes were observed. Both of the two-phase transition processes, i.e., the colloidal crystal-to-liquid transition, which has not yet been detected by dielectric spectroscopy before, as well as the volume phase transition, were detected by the relaxation parameters. Based on the three physical states of the microgel suspension, the relaxation mechanisms are discussed in detail. The slow relaxation originates from the segmental motion and the counterion motion along the polymer chain over the whole temperature range. It was found that when the system is in the colloidal crystal and liquid state, the segmental motion is cooperative with side chain and hydrogen bonding networks, while in the phase separation state (at temperatures above the lower critical solution temperature (LCST)), the cooperative interaction disappears. The fast relaxation is due to the fluctuation of counterions below the LCST and the interfacial polarization above the LCST. Based on interfacial polarization theory, which describes the dielectric model of a conventional particle dispersion, the temperature dependence of the electrical properties for the constituent phases (the permittivity, conductivity and volume fraction of the microgel (εp, κp, ϕ); the conductivity of the medium water (κa); the water content in the PNIPAM microgel (fw)) were calculated using the Hanai equation. The water content is close to the result obtained using light scattering, indicating that the dielectric model for a conventional particle dispersion is also applicable to a soft atypical colloidal dispersion.

How side chains affect conformation and electrical properties of poly(acrylic acid) in solution?

To better understand the effect of side chains on the chain conformation and electrical properties of polyelectrolytes, dielectric measurements were carried out on solutions of poly(acrylic acid) (PAA), poly(acrylic acid)-graft-dodecyl (PAA-g-dodecyl), and poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) over a wide concentration range. Double dielectric relaxations with counterion distribution were observed for these polymers and a refined double-layer polarization model was proposed to analyze these, by which valuable information about conformations and interfacial electrokinetic properties was obtained. The transitional concentrations for the overlapping and entanglement of chains were identified from results for the dielectric increment and relaxation time. The concentration dependences of the ratio of effective charges were estimated from conductivity data. It was shown that effective charges on PAA were greatly influenced by PEO or dodecyl side chains, which caused steric hindrance of counterion binding and further dissociation of carboxylic groups or bound counterions. Moreover, a mutual superposition and offsetting effect of PEO and dodecyl side chains was observed. An enhancement in the interpenetration of counterion atmospheres as a result of side chains was also found. In addition, the rate constant ratio and the distance of counterion fluctuations perpendicular to the chains were estimated. It was demonstrated that the effects of side chains on the effective charges or ionization properties of GCP play an important role in their conformation, counterion distribution, and fluctuation.

Insight into the effect mechanism of urea-induced protein denaturation by dielectric spectroscopy.

Dielectric relaxation spectroscopy was applied to study how urea affects the phase transition of a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), which has been widely used as a protein model. It was found that there is a pronounced relaxation near 10 GHz for the ternary system of PNIPAM in urea aqueous solution. The temperature dependence of dielectric parameters indicates that urea can reduce the lower critical solution temperature (LCST) of PNIPAM, i.e., stabilize the globule state of PNIPAM and collapse the PNIPAM chains. Based on our results, the interaction mechanism of urea on the conformational transition of PNIPAM was presented: urea replaces water molecules directly bonding with PNIPAM and acts as the bridging agent for the adjacent side chains of PNIPAM. Accordingly, the mechanism with which urea denatures protein was deduced. In addition, it is worth mentioning that, from the temperature dependence of the dielectric parameters obtained in the presence of urea, an interesting phenomenon was found in which the effect of urea on PNIPAM seems to take 2 M as a unit. This result may be the reason why urea and TMAO exit marine fishes at a specific ratio of 2 : 1.

Concentration dependent phase behavior and collapse dynamics of PNIPAM microgel by dielectric relaxation.

The dielectric behavior of thermo-sensitive poly-(N-isopropylacrylamide) (PNIPAM) microgel with three different concentrations was investigated for the frequencies ranging from 40 Hz to 110 MHz as a function of temperature from 10 to 60 °C. Two remarkable and temperature-dependent relaxation processes were observed. The slow relaxation originates from the segmental motion over the whole temperature range. The fast relaxation is due to the fluctuation of counterions below the lower critical solution temperature (LCST) and the interfacial polarization above the LCST. It was concluded from the temperature-dependent dielectric parameters that the microgel concentration will not influence the LCST but affects the phase behavior of the microgel suspension: the dense system experienced a colloidal crystal-to-liquid transition and volume phase transition, while the dilute system only underwent a volume phase transition. Based on the interfacial polarization theory, the electrical parameters for the constituent phases (permittivity, conductivity, and volume fraction of the microgel (εp, κp, ϕ) and the conductivity of water κa) and the water content in the microgel (fw) were calculated using Hanai's equation. In addition, the thermodynamics parameters of the two relaxations were calculated from the Eyring equation. The electrical and thermodynamic parameters indicate that the microgel concentration influences the volume, charge density, thickness of the electric double layer, and degrees of freedom of the segments of the microgel, thereby resulting in the differences in collapse dynamics.

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-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 CMC1 of 3 mM and rodlike micelles formed above CMC2, 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(7) 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.

Influence of the structure on the collapse of poly(N-isopropylacrylamide)-based microgels: an insight by quantitative dielectric analysis.

The collapse of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) and poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microgel suspensions is studied by dielectric spectroscopy in a frequency range from 40 Hz to 110 MHz as a function of temperature. Dielectric measurements show that the structure affects the relaxation behavior of microgels: two relaxations (micro-Brownian motion and interfacial polarization at low frequency and counterion polarization at high frequency) are observed in the SIPN microgel whose charges mainly exist in domains and one relaxation (interfacial polarization) is observed in the copolymer microgel whose charges distribute in the whole network. A dielectric model is proposed to describe the collapsed microgel suspensions, from which some parameters, such as the volume fraction and the permittivity of microgels, were calculated using Hanai's equation. The temperature dependencies of these parameters show that the SIPN microgel has better low-temperature swelling properties and thermal responsiveness. This is caused by different polymer-solvent and electrostatic repulsion interactions in different microgels. Compared with pure PNIPAM, the relationship of volume phase transition temperature (VPTT) is VPTTP(NIPAM-co-AA) > VPTTPNIPAM/PAA SIPN > VPTTPNIPAM, and it is explained from the viewpoint of interaction. Besides, the activation energy data prove that the structure influences the electrical properties of microgels, which is consistent with the results obtained from quantitative dielectric analysis.

Dielectric Relaxation of Spherical Polyelectrolyte Brushes: Movement of Counterions and Electrical Properties of the Brush Layer.

Dielectric behaviors of spherical polyelectrolyte brush (SPB) suspensions under various mass fractions of SPB and the pH of solution were investigated in a frequency range of 40 Hz to 110 MHz. The SPB consists of a polystyrene (PS) core grafted with poly(acrylic acid) (PAA) chains. Two unique relaxations were found at either about 10 kHz or 1-10 MHz, respectively, with the former due to the diffusion of counterions and the latter resulting from the interfacial polarization. Using dielectric parameters of two relaxations, we obtained information about the migration of counterion and the conformation of polyelectrolyte chains. The PAA chains are fully stretched when pH is about 8 under the domination of the equilibrium between the penetration and diffusion of counterions in the brushes. A dielectric model is proposed to describe the high-frequency relaxation, and the permittivity and conductivity of SPB and its volume fraction were also calculated on the basis of the model. The surface conductivity of SPB, the Donnan potential, and the fixed charge density in the brush layer were derived from these paramaters. The distribution of the Donnan potential was also simulated by using Poisson-Boltzmann equations, and the result is in accordance with these obtained on the basis of the dielectric model.

The chain conformation and relaxation dynamics of poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl in water: effect of side-chains and distribution of counterions.

We present a study on the dielectric behavior of an aqueous solution of an amphiphilic copolymer, poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl (PAA-g-PEO-g-dodecyl), in the frequency range of 40 Hz to 110 MHz at varying concentrations and temperatures. After eliminating the electrode polarization at low-frequency, three dielectric relaxation processes were observed at about 1.2 MHz, 150 kHz and 30 kHz, whose mechanisms were proved to originate from the fluctuations of free counterions, the fluctuation of condensed counterions, and the rotation of intramolecular aggregates, respectively. The concentration dependence of the dielectric increment Δε and relaxation time τ for these three relaxations presents an abrupt change at 0.15 mg ml(-1), indicating that PAA-g-PEO-g-dodecyl molecules undergo a conformational transition from intramolecular aggregates to intermolecular aggregates. Moreover, both Δε and τ show a clear transition at about 317 K, suggesting a partial collapse of the aggregates. The correlation length and the contour length of the PAA-g-PEO-g-dodecyl chain were estimated according to Ito's theory of counterion fluctuation. It was found that the hydrophobic/hydrophilic side-chains affected the microscopic conformation of PAA, and the hydrogen-bond interactions greatly influenced the conformation. Additionally, the activation energy of these three relaxations was calculated and the process of ionic conduction was studied and the results were used to discuss counterion distribution and ion conduction.

Aggregation behavior and electrical properties of amphiphilic pyrrole-tailed ionic liquids in water, from the viewpoint of dielectric relaxation spectroscopy.

The self-aggregation behavior of amphiphilic pyrrole-tailed imidazolium ionic liquids (Py(CH2)12mim⁺Br⁻: Py = pyrrole, mim = methylimidazolium) in water is investigated by dielectric spectroscopy from 40 Hz to 110 MHz. Dielectric determination shows that the critical micelle concentration (CMC) is 8.5 mM, which is lower than that for traditional ionic surfactants. The thermodynamic parameter of the micellization, the Gibbs free energy ΔG, was calculated for Py(CH2)12mim⁺Br⁻ and compared to those of the corresponding C(n)mim⁺Br⁻ (n = 12, 14). It was found that the main driven forces of the Py(CH2)12mim⁺Br⁻ aggregation were hydrophobic interaction and π-π interactions among the adjacent Py groups. Further, the structure of aggregation was speculated theoretically that Py groups partially insert into the alkyl chains and the staggered arrangement in micelles is formed. When the concentration of Py(CH2)12mim⁺Br⁻ is higher than CMC, two remarkable relaxations which originated from diffusion of counterions and interfacial polarization between the micelles and solution, were observed at about 1.3 MHz and 55 MHz. The relaxation parameters representing the real properties of the whole system were obtained by fitting the experimental data with Cole-Cole equation. A dielectric model characterizing the structure and electrical properties of spherical micelles was proposed by which the conductivity, permittivity and the volume fraction of micelles as well as electrical properties of solution were calculated from the relaxation parameters. An intriguingly high permittivity of about 150 for the micelle was found to be a direct consequence of the strong orientational order of water molecules inside the core of micelle, and essentially is attributed to the special structure of the micelle. Furthermore, the calculation of the interfacial electrokinetic parameters of the micelles, i.e., the surface conductivity, surface charge density and zeta potential, were also achieved based on the relaxation parameters and phase parameters from higher frequency relaxation. On the basis of the results obtained, the aggregation behaviours and interfacial electrokinetic properties of the special micelles are discussed.

Dielectric relaxations of poly(N-isopropylacrylamide) microgels near the volume phase transition temperature: impact of cross-linking density distribution on the volume phase transition.

Dielectric relaxation behaviors of three types of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels with different cross-linking density distributions were investigated in a frequency range from 40 Hz to 110 MHz at temperatures from 15 °C to 55 °C. After eliminating the electrode polarization at low frequency, two remarkable relaxations were observed, one in the kHz frequency range and the other in the MHz range. The low-frequency relaxation is attributed to the counterion polarization in the whole measuring temperature range, while the relaxation at high-frequency is probably dominated by different polarization mechanisms depending on below or above the volume phase transition temperature (VPTT): it is considered as micro-Brownian motion of side groups of PNIPAM when T < VPTT and interfacial polarization when T > VPTT. The temperature dependence of the dielectric parameters for both the relaxations presents an abrupt change around 32.5 °C, indicating the occurrence of phase transition. Based on the analysis and discussion about the micro-Brownian motion of the side groups, a possible microstructure for the microgels before and after the collapse of PNIPAM was suggested. A dielectric model to describe the collapsing microgel suspension was proposed, from which the electrical and structural parameters of the suspension were calculated. The information on the internal structure and hydration dynamic behavior of microgels was obtained by using the thermodynamic parameters which were calculated based on the Eyring equation. Our results reveal that the spatial distribution of the cross-linking density distribution has almost no effect on the volume phase transition temperature, but markedly affects the swelling capacity of PNIPAM microgels at low temperatures.

Electrical transport properties and interaction of heteropolyacid in N,N-dimethylformamide by dielectric spectroscopy.

We present a dielectric spectroscopy study on binary electrolyte solutions composed of N,N-Dimethylformamide (DMF) and heteropolyacid (HPA). The HPA is composed of H(+) and Keggin polyoxometalate anion, [XW12O40](n-)(X = P, Si, with n = 3, 4). Conductivity was used to calculate the transport parameters such as diffusion coefficient and hydrodynamic radius of polyoxometalate (POM) anions. The hydrodynamic radius of P12W40(3-) and Si12W40(4-) are 5.552 Å and 5.526 Å, respectively, indicating that these POM anions remain unsolvated in DMF. The temperature dependences of conductivity obeyed the Arrhenius equation, suggesting that the activation energy of proton conduction process is independent with temperature. The calculated activation energy shows that the conduction process follows Grotthuss mechanism, i.e., proton is transported by hydrogen bond between DMF molecules. One dielectric relaxation observed around 10 MHz is considered to be associated with the POM-DMFH(+) ion-pairs formed by POM and protonated DMF. The interaction between anion and cation in POM-DMFH(+) ion-pairs are explained theoretically based on the Bruggeman's mixture theories and dipole rotation model. From this, the distance between POM and DMFH(+) are estimated as about 1.1 nm.

Dielectric analysis of poly(diallyldimethylammonium chloride) aqueous solution coupled with scaling approach.

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.

Phase transition and electrical properties of aggregations of ethoxylated phytosterol surfactants by dielectric spectroscopy.

The aggregation behaviors of the bio-friendly nonionic phytosterol ethoxylated (BPS-n) surfactants, in water were investigated by dielectric spectroscopy over a frequency range from 40 Hz to 110 MHz. Only the BPS-5 solution system observes dielectric relaxation and we judge this is because due to the difference in the chain length of BPS-n surfactants. Then we further analyze the BPS-5 solution system. Interestingly, we found that BPS-5 lamellar aggregations exist two phases before and after 6%-8% BPS-5 concentration by using the dielectric parameters and the phase parameters obtained by fitting dielectric spectrum and the theoretical model respectively. In addition, we concluded that the change of the electrical parameters such as surface conductivity and zeta potential are related to the lamellar phase structure. Besides, lamellar phases formed at a lower concentration are more stable than those at higher concentration by the thermodynamic analysis.