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.

The interaction between polymer (poly(acrylic acid)) and surfactant 12-2-12 (ethanediyl-1,2-bis(dimethyldodecylammonium bromide)) in aqueous solution was investigated by dielectric relaxation spectroscopy (DRS) over a frequency range from 40 Hz to 110 MHz. To better understand the interaction, the dielectric behaviors of surfactant 12-2-12 solution and PAA solution were also separately studied. For surfactant 12-2-12 solution, one dielectric relaxation was observed above the critical micellar concentration, which was attributed to the interface polarization. For polymer PAA solution, two dielectric relaxation processes were evident which were ascribed to the counterion fluctuation along the whole chain and within the scale of correlation length of PAA polymer respectively. For the mixture of PAA and surfactant 12-2-12 solution, the dielectric behavior was discussed through comparing it with that of PAA and surfactant 12-2-12 solution. The possible interaction pattern and the structure of surfactant 12-2-12/PAA complex were proposed on the basis of the dielectric behavior.

Two nonaqueous ionic liquid (IL) microemulsions (toluene/TX-100/[bmim][PF6] and [bmim][BF4]/TX-100/benzene) were studied by dielectric spectroscopy covering a wide frequency range (40 Hz to 110 MHz). A unique relaxation was observed in the radio frequency (RF) range. By methodically analyzing the dependence of relaxation parameters on the ILs content, the microstructures of the microemulsions were identified. Additionally, based on the interfacial polarization theory and Einstein equation, the mechanism of the relaxation caused by the fluctuation of IL anions along the TX-100 PEO chain was confirmed, what's more, according to the dependence of the dc conductivity of the microemulsions on IL concentration, it was concluded that the hydrophilicity of the IL in the nonaqueous IL microemulsions may play a crucial role in the electrical conduction mechanism: our analysis results suggest that a dynamic percolation process occurs in the toluene/TX-100/[bmim][PF6] system in which IL is hydrophobic, while a static percolation happens in benzene/TX-100/[bmim][BF4] where IL is hydrophilic. The otherness of relaxation time provides evidence that there is a possible coupling effect between IL and TX-100. Moreover, there are hints that all of the disparities, such as relaxation time, percolation type, ion migration rate and the size of different micro zones, may just stem from the different hydrophobicity of the two kinds of IL.

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.

A dielectric spectroscopy study on the binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and four kinds of alcohols as a function of temperature was carried out over a frequency range of 100 MHz to 20 GHz. A wide-band dielectric relaxation was found at about 1 GHz. The relaxation contains the contributions of the IL and alcohols respectively due to the reorientation of the polar cation bmim+ and the cooperative dynamics of the alcohol molecules. The ion conduction ability of the IL in the four alcohols indicates that for IL/methanol and IL/ethanol systems, the interactions between solvents and the IL are stronger than those in IL/propanol (or isopropanol) systems, and the two components may not be uniformly mixed, which are also supported by the analysis of activation entropy. We also found that the isopropanol and propanol molecules have more influence on the rotation of the IL and cooperative motion of alcohols. From the temperature-dependent dielectric spectra, the thermodynamic parameters for the relaxation process such as activation energies, Gibbs free energy, enthalpy and entropy were obtained. It was found that the relaxation process observed in this work is driven by entropy.

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.

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.

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/PAASIPN > 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.

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 107 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.

•Two-relaxation dielectric behavior of polystyrene-poly (butyl acrylate) (PS-PBA) particles was investigated over the frequency range of 40 kHz to 110 MHz.•Phase parameters-the extracted individual electrical information of particles and continuous medium were obtained by Hanai method.•Electrokinetic parameters were obtained on the basis of phase parameters.Dielectric behaviors of suspensions of monodisperse polystyrene-poly (butyl acrylate) (PS-PBA) particles with the radius of 120 nm were thoroughly investigated in the frequency range of 40 Hz to 110 MHz. Two remarkable dielectric relaxations were simultaneously observed, and the well-known Einstein equation and Grosse theory were employed to analysis the relaxation mechanism. Meanwhile, Dukhin-Shilov theory about the thin double layer of colloid dispersion was employed to verify the effects of volume fraction and KCl electrolyte concentration on dielectric parameters of DRS. The results showed that the changing trend of relaxation frequencies and dielectric increments from experimental data with KCl concentration and volume fraction was well consistent with the prediction of the wide-range DRS of Dukhin-Shilov theory. In addition, the reasonable phase parameters (εpεp,κpκp,εaεa,κaκaandϕϕ) were calculated by Hanai theory on the basis of the suggested dielectric model. Finally, the interfacial electrical parameters (λλ,σσ,ζζ) of PS-PBA microspheres dispersed in different concentrations of KCl electrolyte solution were obtained by electrodynamics equations about interface on the basis of dielectric analysis. More importantly, the calculated value of ζζ well agreed with the value (- 48.8 mV) measured by Zeta potential analyzer, thus the result proved that DRS was a feasible method to investigate the interfacial electrical parameters of disperse system in a non-intrusive way.Three-dimensional representations of KCl concentration (a) and mass fraction of PS-PBA particles in suspension (b) dependences of the derivative dielectric loss spectra. Note: They have been processed by eliminating the electrode polarization. The arrows indicated the low- and high- relaxation frequencies.

The thermally sensitive charged poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) spherical microgel was prepared and their temperature-dependent volume phase transition behavior was systematically studied by analyzing the dielectric spectroscopy theoretically over a frequency range from 40 Hz to 110 MHz. It was found that the dielectric relaxation of the charged P(NIPAM-co-MAA) microgel drastically changed between 30 and 35 °C, and was significantly different from that of neutral PNIPAM microgels recently published in Soft Matter. The relaxation mechanism was speculated and the relaxation parameters were fitted after successfully eliminating the electrode polarization at low-frequency. On the basis of this, the differences in the structure, swelling ability and dehydration dynamics between charged P(NIPAM-co-MAA) and neutral PNIPAM microgels were compared. Although both of the two microgels showed the same changing trend around the volume phase transition temperature (VPTT), VPTT of charged P(NIPAM-co-MAA) microgels is less markedly than that of neutral PNIPAM. This suggests that the interaction between the PNIPAM chains and the solvent was changed significantly because of the introduction of charged groups. The volume phase transition behavior of P(NIPAM-co-MAA) microgels controlled by a delicate balance between the hydrophobic attraction of NIPAM and the electrostatic repulsion of the carboxylate group of methacrylic acid (MAA). These interactions are the essential reasons of the changes of the charged microgels in structure, swelling ability, and dehydration dynamics.

•Two dielectric relaxations for SPBs suspension are observed the relaxation mechanisms are confirmed as counterion movement and the interfacial polarization.•The movements of counterion two kinds of modes: tangential movement for collapsed SPBs and diffusion movement along the brush for stretched SPBs.•The collapsed and stretched brushes are PS-PAA in acidic solution and PS-PAA in larger pH solution, PS-PAEMH in acidic solution, respectively.•The surface conductivity and the particle surface charge density and the Zeta potential of PS-PAA1, 2, 3 are estimated theoretically•The response of polyelectrolyte brush to acidity of medium, mass fraction of SPB the brush length are calculated by the dielectric spectrum.Dielectric behaviors of spherical polyelectrolyte brushes (SPBs) suspensions with different properties, length brushes under various mass fractions of SPBs and pH of solution were investigated in a frequency range of 40 Hz to 110 MHz. In this paper, the SPBs consist of polystyrene (PS) core and the negative poly(acrylic acid) (PAA) named PS-PAA of different length and cationic poly(2-aminoethylmethacrylate hydrochloride) (PAEMH) chains named PS-PAEMH grafted on the polystyrene (PS) core. Two unique relaxations are found at either about 10 kHz or 1−10 MHz, respectively, the former due to the movement of counterions and the latter resulting from the interfacial polarization. Using dielectric parameters of the high-frequency relaxation and the Cell model, the information about the brush length, the volume fraction, the electrical and phase parameters of the SPBs and the bulk solutions can be obtained. The surface conductivity of SPBs, the Zeta potential, and the fixed charge density in the SPBs also can be derived. While the low-frequency relaxation shows two separate mechanisms when the brushes are collapsed and stretched: tangential movement of counterions along the SPB particles for PS-PAA with different mass fraction; diffusion movement of counterions along the brush between the brush and the bulk solution for PS-PAA with different pH, PS-PAEMH with different mass fraction, respectively. Significantly larger conductivity and relaxation strength are obtained for PS-PAA with longer brushes. PAA brushes exhibit a transition with increasing pH in which the chains are stretched from collapsed to nearly full length under the domination of the equilibrium between the penetration and diffusion of counterions in the brushes. We found that cationic SPB PS-PAEMH, whose brush dissociation degree is bigger than PS-PAA with negative brush in the acidic solution. These findings lay the foundation for different SPBs’ different applications.Two remarkable relaxations are observed for the SPBs (composed of PS core and PAA and PAEMH chains) suspension, and the mechanisms of the relaxations are confirmed the movement of the counterions (low-frequency relaxation) and the interface polarization between SPB and solution (high-frequency relaxation). The movements of counterion in the SPBs suspension are revealed as two kinds of modes: tangential movement of counterions along the SPB particles for SPBs with collapsed brushes (the collapsed PS-PAA in the acidic solution) and diffusion movement of counterions along the brush between the brush and the bulk solution for SPBs with stretched brushes (the strentching PS-PAA in the basic solution and PS-PAEMH in the acidic solution). From high-frequency relaxation the response of polyelectrolyte brush to acidity of medium is detected. Further, combining dielectric parameters obtained and the theory equations presented by O'Konski, surface conductivity λλ and the particle surface charge densityσσ and the Zeta potential ςς of PS-PAA1, 2, 3 are obtained. Combining dielectric parameters obtained and the cell model, the phase parameters of the SPBs can be obtained.

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.

The phase behavior of 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6], a hydrophobic ionic liquid (IL)), polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100, a nonionic surfactant with a polyoxyethylene chain), and ethylene glycol (EG) ternary nonaqueous systems, was studied by dielectric relaxation spectroscopy (DRS). In single-phase region, EG-in-IL (EG/IL), bicontinuous (B.C.), and IL-in-EG (IL/EG) subregions can be identified by the dc conductivity. The inflection points of the relaxation parameters (dielectric intensity and relaxation time) are consistent with the phase boundaries between IL/EG and B.C. and B.C. and EG/IL subregions, which imply that the change of microstructure of this system can be detected by the dielectric response. Furthermore, in IL/EG microregion, phase parameters of constituent phases were calculated based on interface polarization theory. The trends of relaxation times for both of the calculated values τMW and experimental values τ as a function of IL content in IL/EG microregion are almost the same, which infers that the dielectric relaxation originates from the interfacial polarization. This work is helpful to understand the dynamics and phase behavior of nonaqueous microemulsions.

A new experimental result from dielectric spectroscopy of poly(N-isopropylacrylamide)/poly(acrylic acid) semi-interpenetrating polymer network (PNIPAM/PAA SIPN) microgel, which undergoes significant volume phase transition, is reported. Two significant dielectric relaxations were observed around 0.1–0.5 MHz and 1–5 MHz, respectively. The high-frequency relaxation is attributed to the migration of counterions tangentially and radially along the domain formed by linear PAA chains (counterion polarization). The temperature dependence of the domain size obtained from this relaxation shows that the SIPN microgel with higher content of PAA has better thermal response and swelling property. The low-frequency relaxation shows two separate mechanisms below and above the volume phase transition temperature (VPTT), which are dominated by different relaxation processes, respectively: micro-Brownian movement of solvated side groups of PNIPAM dominates when T < VPTT, while the interfacial polarization does when T > VPTT. A dielectric model was proposed to describe the collapsed microspheres suspension, from which the electrical parameters of microgel were calculated. The permittivity of microgel shows that a special ordered arrangement of water molecules is formed in microgel with less PAA. Thermodynamic parameters obtained from Eyring equation reveal that the difference in PAA content has a great influence on the thermodynamics of the phase transition process. Besides, it was found that the VPTT of the SIPN microgel was significantly increased compared with pure PNIPAM hydrogel microspheres. The essence of anomalous VPTT revealed by relaxation mechanism is the difference in composition content leading to different hydrophilic/hydrophobic and electrostatic interaction. Determining the reason for anomalous VPTT is of instructive significance to understand the volume phase transition of complex polymer materials.

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 Cnmim+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.

This work reports the dielectric analysis of three kinds of nanofiltration membranes (NF90, NF- and NF270) in eight electrolyte solutions. The high-frequency relaxation was analyzed theoretically and the relative permittivity and conductivity of the wet-membranes were calculated. Porosity of these membranes and ion solvation energy barrier were calculated using the relative permittivity of the wet-membrane. By combining the conductivity ratio of membrane and solution, κm/κw, with the TMS model, the volumetric charge density of the membranes was estimated. The concentration expressions of co- and counter-ions in the membranes were deduced based on the Donnan exclusion theory. The wet membrane's relative permittivity rather than the dry one was used in all of the calculations, so the results are very close to the practical separation process. Furthermore, the influencing factors on the ion permeability for three types of NF membranes were discussed by considering the ion concentrations inside the membranes, ion solvation energy barrier and the surface charge density on the pore-wall.

Dielectric relaxation studies were conducted on the ternary systems of the nonionic surfactant Triton X-100 (a nonionic surfactant with a polyoxyethylene chain)/toluene/water in the frequency range from 40 Hz to 110 MHz. The contents of water and toluene were varied separately while the ratios of the other two components were fixed. Remarkable dielectric relaxations were observed around 1 MHz and dielectric intensity shows different variation with the increase of the contents of water or toluene. Dielectric parameters were obtained by fitting the data using the Cole–Cole equation with one dispersion term. The reverse micelles, water-in-oil, and oil-in-water micro-regions of the microemulsions were identified by the dependence of conductivity of the dispersed phase and continuous phase on the contents of water or toluene. Hanai theory and the corresponding analysis method were used to calculate the phase parameters of the constituent phases. The analysis results suggest that the dielectric relaxation probably arises from the interfacial polarization.

•Microstructure and structural transitions vary with ethyleneglycol content.•Dielectric parameters were obtained by fitting Cole–Cole equation.•Hanai method was employed to estimate the phase parameters.•Result of dielectric analysis was confirmed reasonable by interfacial polarization.The ternary system consisting of ethyleneglycol (EG), an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [Bmim][PF6]) and a nonionic surfactant (p-(1,1,3,3-tetramethylbutyl)phenoxypolyoxyethyleneglycol, TX-100) was studied by dielectric measurements in the frequency range from 40 Hz to 110 MHz. A remarkable dielectric relaxations caused by interfacial polarization was observed around 10 MHz. The dielectric intensity Δɛ and the relaxation time τ could be obtained by fitting the experimental data using the Cole–Cole equation with one dispersion terms. The regions of EG-in-IL (EG/IL), bicontinuous phase (B.C.), IL-in-EG (IL/EG) microemulsions and dilute solution were identified by the dependence of direct current (dc) conductivity on the content of EG, where the dc conductivity was obtained from the total dielectric loss spectra. The scaling relation between conductivity and the content of EG was compared with the predictions of scaling theories. In the IL/EG micro-region, Hanai theory was used to calculate the phase parameters of the constituent phases. The trends of calculated relaxation time τMW and τ as a function of EG content in the IL/EG micro-region were almost the same, inferring that the dielectric relaxation probably arose from the interfacial polarization. In short, this work is helpful to understand the microstructures of different regions and percolation phenomenon in nonaqueous microemulsions.Dependence of (a) permittivity ɛ′ and (b) dielectric loss ɛ″ spectra of ternary systems of EG/TX-100/[Bmim][PF6] with different EG contents.

The aggregation behavior of C6mimBr and its interaction with water at different concentrations and temperatures have been investigated by dielectric spectroscopy over frequency ranges from 500 MHz to 40 GHz. Dielectric determinations show that micellar aggregations form when the C6mimBr concentration is higher than 0.85 M, and the size of micellar aggregations varies inversely to temperature. The thermodynamic quantities of the micellization at different temperatures, ΔGm, ΔHm, and ΔSm were calculated, and it was found that the main driving forces of C6mimBr aggregation were controlled by different thermodynamic quantities at different temperatures: the micelle formation process is controlled by an enthalpy effect at low temperature while it is entropically driven at high temperature. Two remarkable relaxations that originate from the orientation polarization of “bulk water” and “bound water” interacting with C6mimBr were observed at about 8.2 and 15 GHz. The relaxation parameters obtained by fitting the dielectric spectra data were used to estimate the number of bound water per C6mim+ in the micellar core. The enthalpy and entropy closely linked to the relaxation processes of bound water and bulk water were calculated using the relaxation time according to Eyring equations. The average number of hydrogen bonds of a C6mimBr–water system in different microenvironments was calculated, and the essence of cooperative orientation dynamics of water was described.

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 behaviors of poly(acrylic acid) (PAA), poly(acrylic acid)-graft-dodecyl (PAA-g-dodecyl), and poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) solutions were investigated from 40 Hz to 110 MHz at the solution temperature of 26 °C. For PAA and PAA-g-dodecyl solutions, two dielectric relaxations at about 5 MHz and 150 kHz were observed, whose mechanisms were proved to be the fluctuation of free counterions and condensed counterions, respectively. While for PAA-g-PEO solutions, an extra relaxation around 30 kHz was observed, including the two relaxations just mentioned, and it is related to the hydrogen-bonding aggregates in PAA-g-PEO solutions and was attributed to the rotation of the whole molecule. And no relaxation processes caused by dodecyl or PEO side-chains were detected in our measuring frequency range. Based on Mandel’s model, some parameters characterizing the structure of polyelectrolyte chain, such as radius of gyration and Kuhn segment length, were obtained. Both PAA-g-PEO and PAA-g-dodecyl molecules adopt a more compact conformation than PAA, owing to the formation of hydrogen-bonding aggregates and hydrophobic microdomains, respectively. The introduction of dodecyl and PEO side-chains weakens the intramolecular hydrogen-bonding interactions in PAA molecule and makes the flexibility of PAA-g-PEO and PAA-g-dodecyl chains greater than PAA chains.

•Real-time monitoring of dielectric measurements was performed by DRS.•Dielectric parameters were obtained by fitting Cole–Cole equation to DRS data.•Hanai method was employed to estimate the phase parameters.•Dependences of the obtained parameters on the extractive time were investigated.•Result of dielectric analysis was confirmed reasonable by interfacial electrokinetic model.Real-time monitoring of dielectric behaviors of CMPS-supported imidazolium ionic liquids (ILs) microspheres in model gasoline was performed by dielectric relaxation spectroscopy (DRS) from 40 Hz to 110 MHz. One dielectric relaxation in MHz frequency range is obviously observed for all systems and determined to be closely related to the interfacial polarization. The interfacial polarization is attributed from the different conductivities between dispersed microspheres and model gasoline since imidazolium-based ionic liquids have been immobilized on the surfaces of dispersed microspheres in the form of optimized spatial configurations. Meanwhile, dielectric parameters (ɛl, κl, ɛh, κh and f0) for all the systems are obtained by fitting Cole–Cole equation to the dielectric data. From the dielectric parameters, Hanai equations are employed to calculate phase parameters (ϕ, κm, ɛp and κp), which is used to characterize the electrical and structural properties of constituent phases of suspensions of conducting particles in non-conducting medium. The time-dependences of dielectric parameters and phase parameters are investigated in detail, and interfacial electrokinetic model for suspension of dense particles has been employed for interpreting these time-dependences. Here, we found that possible π–complexation bond and π–π interaction between imidazole rings of ILs and thiophene are responsible for time-dependences of all parameters. Furthermore, the time-dependences of parameters indicate that the electron density (polarization strength) on surfaces of dispersed microspheres decreases with the increment of extraction time.Dependences of (a) permittivity ɛ′(ω) and (b) dielectric loss ɛ″(ω) spectra of suspension of CuCl/CMPS-Im(Cl) microspheres in model gasoline on extractive time.

The adsorption process of salicylic acid (SA) onto chitosan membrane is monitored in real time by the dielectric relaxation spectroscopy (DRS) method. A unique dielectric relaxation, which is related to the macroscale concentration polarization layers (CPLs) in the SA solution caused by the adsorption, is observed. By modeling the measured systems composed of the membrane, the CPLs, and the SA solution, the dielectric spectra are analyzed systematically on the basis of the interfacial polarization theory. The parameters about the constituent phases, i.e., the dielectric constant εm and the conductivity κm of the chitosan membrane, the conductivity distribution (κ1 to κ2), and the thickness dCPL of the CPL, are obtained. The time-dependent εm and κm give insight into the microstate of the chitosan membrane during the adsorption. Furthermore, the time evolution of the conductivity gradient of the CPL, Δκ/dCPL, is combined to interpret the adsorption mechanism. It is suggested that the noninvasive dielectric monitoring may be applied to many adsorption and release processes.

Dielectric behaviors of titanium dioxide (TiO2)-based electrorheological (ER) suspensions with different particle concentrations and TiO2 polymorphs were investigated in the frequency range of 40 Hz to 110 MHz. Two relaxations in kilohertz and megahertz frequency range were attributed to interface polarization between TiO2 and silicone oil and ion pair polarization between dissociated counterions and fixed charges on TiO2 surfaces, respectively. Dipolar coefficient D, which is related to the construction or structure of the colloid, changes after critical volume fraction \(\phi _{\rm c} \approx \) 0.05, indicating that chain-like or network structures are formed by particles. Based on percolation model, the values of critical exponent suggest that particles may form two-dimensional percolation network. Furthermore, the effective dielectric mismatch parameter, \(\beta _{\rm eff}\), was calculated based on the obtained phase parameters. We found that rutile should have better ER activity than anatase. The main reason for weak ER activity of pure TiO2 ER suspensions may due to poor conductivity properties of TiO2 crystals.

The interaction between the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and ethanol and the micro phase behavior for the binary system have been investigated by dielectric relaxation spectroscopy (DRS) over a frequency range from 10 MHz to 20 GHz under constant temperature. The dielectric spectra with two relaxation processes were observed, and it could be satisfactorily fitted by an empirical equation including a non-Debye process at lower frequencies and a Debye process at higher frequencies. Detailed analysis indicates that either of the two relaxation processes contain the contributions of different polarization mechanisms, respectively. The low-frequency process, centered at about 1 GH is mainly due to the reorientation of the polar cation [bmim]+ and ion pairs formed between cation and anion of the IL and cooperative dynamics of the ethanol H-bond system; the high-frequency one, located at about 10 GHz is caused by the fast fluctuation of ion-pairs formed between cation and anion of the IL within the inter-ion distance and the rotation of singly H-bonded ethanol monomers at the ends of the ethanol chain. The ethanol concentration dependency of all the relaxation parameters shows a inflection point at the ethanol mass fraction of 20%, which is consistent with macro phase diagram. This inflection point is the cut-off point of one phase and two phase. The dielectric analysis indicates that a great micro-structure difference exists above and below 20%.

Dielectric properties of PAA-g-PEO-7% solutions with different counterions were measured as a function of concentration and temperature over a frequency range of 40 Hz to 110 MHz. After the contribution of electrode polarization effects was subtracted, the dielectric spectra of PAA-g-PEO-7% solutions showed three relaxation processes in the experimental frequency range, named low-, mid-, and high-frequency relaxation. The observed three relaxations were strictly analyzed by using the Cole–Cole relaxation function, and the dielectric parameters (dielectric increment Δε and the relaxation time τ) were obtained. The scaling relation of dielectric increment and relaxation time of high frequency with concentration Cp were obtained and compared with the predictions of scaling theories. The information on the dynamics and microstructure of PAA-g-PEO-7% was obtained. Using different counterion species, the mid- and high-frequency relaxation mechanisms were attributed to the fluctuation of condensed counterions and free counterions, respectively, and the low-frequency relaxation was considered to be caused by the interface polarization of a complex formed by the hydrogen bonding between carboxylic group of PAA and ether oxygen on the side-chain PEO. In addition, by means of Eyring equation, the thermodynamic parameters, enthalpy change ΔH and entropy change ΔS, of the three relaxations were calculated from the relaxation time and discussed from the microscopic thermodynamical view.

Iron doped chitosan microspheres (IDM) with different concentrations of iron (wt.%) were prepared and dielectric behavior of the IDM suspensions was investigated in the frequency range from 40 Hz to 110 MHz. Dielectric spectra of these suspensions showed distinct relaxations at MHz frequency range which are attributed to the interfacial polarization between IDM particle and medium solution. The relaxation varied with the concentration of iron (wt.%) in IDM and the changing trends of relaxation parameters showed that: an appropriate iron doping concentration can increase adsorption capacity of chitosan, however, when the doping concentration exceeds a certain value, the capacity will be reduced. Furthermore, the phase parameters of the suspensions were calculated by using Hanai method. The obtained permittivity ɛp of IDM demonstrates a significant change with the iron concentration (wt.%). In addition, the interfacial electrokinetic parameters, surface conductivity λ, charge density σ and zeta potential ζ, were also estimated from the phase parameters and these parameters indicate that: the interfacial properties between the IDM and continuous medium were little affected by iron concentration in IDM.Graphical abstractElectric properties such as permittivity ɛp and zeta potential ζ of chitosan–iron composite microspheres (IDM), which were influenced by iron doped concentration in IDM, were obtained just by analyzing dielectric spectra.Highlights► Dielectric properties of iron doped chitosan (IDM) suspensions were discussed. ► The electrokinetic parameters for IDM were obtained just by dielectric analysis. ► Excessive doping content causes opposing effect on chitosan adsorption capacity.

Dielectric measurements were carried out for binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and Triton X-100 (TX-100, a nonionic surfactant with a polyoxyethylene chain), and [bmim][PF6]/TX-100/water ternary systems in a wide frequency range, to study the molecular interactions and percolation in these systems. Striking dielectric relaxations were observed. The dc conductivity data (obtained from the total dielectric loss spectra) have interesting dependencies on the variation of sample composition. In TX-100/[bmim][PF6] solutions, the dependence of dc conductivity on volume fraction of TX-100 was analyzed in light of the Bruggeman's effective-medium approximation, which indicates that the number of imidazolium cations associated with every TX-100 molecule is ten. The water-in-IL, bicontinuous, and IL-in-water micro-regions of the microemulsions were identified by the dependence of dc conductivity on water mass fraction. The dc conductivity data were partly explained by the percolation theory, which suggests that a static percolation occurs in this hydrophobic IL microemulsion. When the mass concentration of water is more than 80 wt%, dc conductivity linearly decreased with the increase of water concentration, which implies that [bmim][PF6] may dissolve in water rather than forming an ionic liquid micro-pool. The dependencies of dc conductivity as a function of IL-to-TX-100 molar ratios in three different sub-regions were explained by the microscopic interaction mechanism, which infers that the hydrophilicity of poly(oxyethylene) chain in TX-100 is stronger than its IL-loving nature, and the microemulsions are “softer” in the W/IL micro-region.

Dielectric measurements were carried out for the systems composed of nanofiltration membranes and electrolyte solutions over a frequency range of 40 Hz to 10 MHz, and double dielectric relaxations were observed at about 102–106 Hz. Based on the interfacial polarization theory, the dielectric relaxation at high frequency was analyzed theoretically, and the permittivity and conductivity of the membrane and electrolyte solutions, were obtained. By using the permittivity of wet membrane, the ion solvation energy barrier in eight electrolyte solutions was calculated. The results showed that the ion solvation energy barrier of 2-2 type of electrolyte solution was the biggest among all types of electrolyte. The influence of solvation energy barrier on separation performance was also evaluated. Because the permittivity of wet membrane takes the place of that of dry membrane, the calculations can ensure more accurate results close to practical separation process. Furthermore, the variation of the ratio of membrane/solution conductivity, κm/κw, with the electrolyte concentration was explained by Donnan equilibrium theory, and the ratio together with the TMS model was used to calculate the volume charge density of membrane. On the basis of this, by using the volume charge density of membrane and the existing transport models, such as TMS, TMS-DE, DSPM model, four transport parameters were calculated. It was concluded that in the process of ion permeation through the membrane, Donnan exclusion is the most important influencing factor and steric effect is secondary in low electrolyte concentration, whereas dielectric exclusion plays a dominant role in high electrolyte concentration.Highlights► We studied dielectric spectroscopy of NF membrane immersed in electrolyte solutions. ► We used method of dielectric analysis coupled with the transport models. ► Information on ion permeation membrane were obtained. ► Transport parameters of membrane were obtained using dielectric parameters.

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 C10SO4Na solution, dielectric relaxation was observed at submicellar concentrations, which is ascribed to the counterion diffusion around premicelles. For the aqueous solutions of a PDADMAC/C10SO4Na 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.

Dielectric measurements were carried out on binary mixtures of Triton X-100 (TX-100, a nonionic surfactant with a polyoxyethylene chain) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4], a hydrophilic ionic liquid), and [bmim][BF4]/TX-100/cyclohexane microemulsions in a wide frequency range to study the molecular interaction and percolation in these systems. Striking dielectric relaxations were observed, and the dc conductivity data were obtained from the measured total dielectric loss spectra. The interaction between TX-100 and [bmim][BF4] is estimated by analyzing the dc conductivity of TX-100/[bmim][BF4] solutions in light of the Bruggeman’s effective medium approximation, which indicates that spherical micelles are formed when the TX-100 volume fraction is below 48% and the number of cations associated with every TX-100 molecule is eight. For IL–oil microemulsions, both the dependence of dc conductivity and the permittivity (for fixed frequency) on cyclohexane concentration were used to identify the oil-in-IL, bicontinuous, and IL-in-oil microregions. Both the conduction and dielectric relaxation behavior suggest that a static percolation occurs in this hydrophilic IL microemulsion.

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 °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.

The release processes of salicylic acid (SA) from the chitosan gel beads (CGB) with different crosslinking densities were monitored in real time by means of dielectric spectroscopy. Distinct dielectric relaxations attributed to interfacial polarization were observed, which exhibited obvious dependences on the crosslinking density and the release time. In line with Hanai’s equation, the properties of CGB and release media were quantitatively determined from the dielectric profiles. Based on these properties and dielectric behaviors, the release profiles were analyzed. It was found that only the dispersion of CGB with the lowest crosslinking density exhibited release behavior, while other dispersions showed an obvious adsorption process following a burst of drug diffusion. The total loading and release amount of SA were determined and compared, and the influence of crosslinking degree on the drug loading and release was discussed. In addition, the release behavior was confirmed to be diffusionally controlled, and the diffusion coefficient of SA was determined.

The chitosan microspheres loaded with model drug, salicylate molecular, are prepared, and the dielectric spectroscopy of this kind of suspension is measured, meanwhile a significant relaxation is observed for the microspheres suspension. By the modeling analytic of the relaxation, the parameters, which can reflect the properties of microspheres and continuous medium, are obtained. Furthermore, the releasing process of microspheres in aqueous phase is monitored real-timely, namely, by analyzing the time-dependent variation of the parameters reflecting the relaxation characteristics and electrical parameters in each phase the releasing process is detected. The research shows that the controlled release process of chitosan microspheres loaded with salicylate in aqueous phase is divided into three phases according to different releasing mechanisms. At the release stage, the quantitative relation between the phase parameters obtained by dielectric analysis and the amount of the salicylate carried in microspheres was derived, and a real-time monitoring method was established through releasing material in the microspheres at different times obtained by measuring and analyzing the dielectric spectroscopy.

The dielectric spectra of nanofiltration membranes NF90, NF-, and NF270 in eight electrolytes, NaCl, KCl, CuCl2, MgCl2, Na2SO4, K2SO4, MgSO4, and CuSO4, were investigated as a function of the electrolyte concentration over a frequency range from 40 Hz to 11 MHz. Two relaxations were observed: the one at high frequency was caused by interfacial polarization between the membrane and electrolyte, and the low-frequency relaxation, on which we focus on in this work, was confirmed to be due to the counterion polarization effects in the pores of the membrane. A model of cylindrical pores which were dispersed in membrane base was developed to interpret the low-frequency relaxation. On the basis of this model, we amended the expression deduced by Takashima for describing the dielectric behavior of a cylinder particle suspension to fit our dielectric data from the low-frequency relaxation. The data fitting with this improved expression was suitable for all the systems measured in this work; structural and electrical parameters such as the radius of the pore in the membrane, the thickness of the active layer of the membrane, surface charged density, and zeta potential on the pore wall were obtained finally.

The dielectric behavior of suspensions of polystyrene/zinc oxide (PS/ZnO) composite particles in aqueous and electrolyte solution have been investigated by dielectric relaxation spectroscopy (DRS) in the frequency range from 40 Hz to 110 MHz. Two relaxations were confirmed by means of the logarithmic derivative method in this frequency range, which turned out to be very effective in resolving overlapped relaxations. The effects of volume fraction and the electrolyte concentration of composite particles on the dielectric response of suspensions were examined in detail, respectively. According to dielectric analysis, we found an abnormal and significative phenomenon, namely, special dielectric increments, where ∂εl = (εl − εm)/φ and ∂εh = (εm − εh)/φ denoting the low- and high-frequency relaxation amplitude of suspensions of PS/ZnO particles per unit volume, respectively, were increasing with the enhancement of volume fraction φ. On the basis of the combination of studying the dielectric parameters by fitting data with the Cole−Cole equations and phase parameters calculated by Hanai method, we proposed that except for the two distinct relaxations, the low- and high-frequency relaxations which are occurred at lower kilohertz and higher megahertz frequencies, respectively, suspensions exhibit an additional dielectric relaxation over the megahertz frequency range, here named “the third relaxation”, due to the polarization of internal double layer of the thin layer of semiconducting ZnO when an external field is applied.

Dielectric relaxation spectroscopy (DRS) was carried out on hydrated NaA zeolite (LTA) with various high pretreatment temperatures (PT), and the effect of thermal treatment on crystal structure was characterized by X-ray diffraction analysis (XRD). A dielectric relaxation about 105 Hz was found to be closely related to the integrity of the pore framework, and the decreased relaxation increment was attributed to the structural evolution of LTA. The critical temperature (CT), where the crystal structure of LTA starts to essentially change, was jointly determined by DRS and XRD. Comprehensive investigation of the relaxation mechanism and time indicated symmetrical shrinkage of pore channels at thermal PT below CT. The Hanai method was used to calculate the dielectric properties of LTA particles and aqueous medium. The invariant permittivity of particles indicated the thermal stabilization of polarization distribution of sodium ions, and the decreased particle conductivity with PT increasing to CT reflected the negative effect of thermal pretreatment on the mobility of sodium ions. The abnormal conductivities of particles and medium indicated prior sintering on the pore’s surface at the beginning of crystal structure transition.

Dielectric monitoring of the adsorption or release process of salicylic acid (SA) by chitosan membrane shows that the dielectric spectra of the chitosan membrane/ SA solution systems change regularly in the adsorption or release process. By analyzing the regularity, a new mechanism for the relaxations is proposed. The concentration polarization layer (CPL) caused by SA adsorption or release is confirmed to be essential for the dielectric relaxations. The changes of the spectra with time are explained by account of the relationship between CPL properties and dielectric strength. Based on this relaxation mechanism, a theoretical method can be established to calculate dynamical parameters of inner structure of the adsorption or release systems from their dielectric spectra. Therefore, dielectric spectroscopy is demonstrated to be a promising method for estimating interfacial distribution of ionic substances and their binding to membrane in a non-invasive way.

The dielectric properties of 4A zeolites dispersed in silicone oil are measured in the frequency range of 40 Hz to 110 MHz for elucidating the dielectric background of zeolites electrorheological (ER) fluid, and two relaxations are observed. The possible mechanisms of the dielectric relaxations are suggested that the transfer motion of sodium ions in supercage is contributed to the low-frequency relaxation, and the high-frequency relaxation is raised from the hopping of sodium ions restricted on active sites. The dielectric analyzing indicates that appropriate concentration, presence of water in cavity and the frequency strongly affect the motion of sodium ion inside the solid-state framework. As well as the analysis of the phase parameters offers real permittivity of zeolite particle under electric field, and insures the accurate calculation for electrostatic interaction of dipole.

In this work, we aim to contribute new data on the dielectric relaxation behavior of suspensions of nonconducting/conducting composite microspheres (polystyrene/ polyaniline, PS/PANI). Then, the dielectric investigation over the frequency range of 40 Hz to 110 MHz has been carried out to display the characteristic of dielectric relaxation spectroscopy of suspensions with PS/PANI composite microspheres from two contributions which are the dependences of dielectric relaxation spectroscopy of suspensions on the volume fraction of particles (ϕ) and temperature (T), individually. Two relaxations can be identified in dielectric spectroscopy of suspensions: the so-called α- relaxation (typically at kHz) due to the polarization of counter-ions, and the Maxwell−Wagner−O’Konski (M−W−O) relaxation (typically at MHz) ascribed to a consequence of an accumulation of polarized charges on the boundary surfaces of the dispersed particles. The dependences of dielectric parameters by fitting data with Cole−Cole equations on ϕ and T have been discussed in detail, respectively. According to the dielectric analysis, several interesting phenomena arise in the range of investigation: First, special dielectric increments, where ∂εl = (εl − εm)/ϕ and ∂εh = (εm − εh)/ϕ denoting the low- and high-frequency relaxation amplitude of suspensions of PS/PANI particles per unit volume, respectively, are increasing with the enhancement of volume fraction ϕ. Second, all high-frequency permittivities (εh) are higher or much higher than the permittivity of aqueous solution (80.05 at 18 ± 1 °C). On the basis of the comparisons between PS/PANI and PS, PS/PPY, PS/ZnO particles, we extract some proposals to responsible for such interesting phenomena, namely, except for the two distinct relaxations, α-relaxation and M−W−O relaxation, suspension exhibits an additional dielectric relaxation over the megahertz frequency range, due to the polarization of internal double layer of the thin layer of conducting polymer PANI when an external field is employed. Meanwhile, the different dependences of εh on ϕ for suspensions of PS/PANI (PS/PPY) and PS/ZnO particles are ascribed to the different conducting mechanism and surface morphology of conducting polymer PANI (PPY) and ZnO shells. Finally, after the detailed analysis we obtained the activation energy Ea of the low- and high-frequency relaxations of suspensions of PS/PANI microspheres which is experimentally determined by the dielectric data, individually.

The nonionic APG/n-butanol/cyclohexane/water microemulsions with different microstructure, which is induced by the variation of water contents, are investigated by the dielectric spectroscopy. An appropriate dielectric theory, Hanai theory and the corresponding analytical method are applied to obtain the internal properties of the constituent phases of microemulsions, such as the relative permittivity and conductivity of continuous and dispersed phases and the volume fraction of dispersed phase. Using these parameters, the distribution of n-butanol in constituent phases, which is of important in the study field of the microstructure of microemulsion, is obtained quantitatively. It is found that the n-butanol molecules not only distribute in the interfacial APG layer but also in the continuous and dispersed phases. In addition, the percolation threshold is interpreted by using the dynamic percolation model. The structural and dynamic information are obtained, for instance, the critical volume fraction of water when percolation occurs and the characteristic time for the rearrangement of clusters. These parameters are intimately related to the properties of microemulsions, especially the characteristics of the interfacial layer.Dielectric spectra of APG/n-butanol/cyclohexane/water microemulsions with different microstructures are analyzed by using Hanai method. The distribution of alcohol in the constituent phases of microemulsions is obtained from the analytical results.

Dielectric properties of E. coli cells before and after Cu2+ incubation were investigated by using the dielectric spectroscopic technique. The dielectric spectra are analyzed theoretically by means of the extended three-shell ellipsoidal model, which can reflect the complicated morphological structure of E. coli cell including the outer membrane, the periplasmic space, the inner membrane and the cytoplasm. The results showed that dielectric properties of these cellular components were changed with Cu2+ treatment in a time- and concentration-dependent way. The permttivity of the outer membrane increased with the incubation time and concentration of Cu2+, possibly because polarizability of the outer leaflet of lipopolysaccharides was affected by Cu2+. The conductivity of the periplasmic space decreased with the incubation time and concentration of Cu2+, possibly due to the damage of peptidoglycan. The decreased permittivity of the inner membrane may be caused by disturbance of the lipid bilayer structure produced by Cu2+ incubation. The decreased cytoplasmic conductivity may be the consequence of the leakage of K+ from it. The cytoplasmic permittivity decreased with Cu2+ treatment probably because of the leakage of its some components.

The dielectric properties of polystyrene-polypyrrole (PS-PPy) core-shell conducting particles approximately defined as the uniform spheres in aqueous solution, were investigated in this work by dielectric relaxation spectroscopy (DRS) over a frequency range of 40 Hz to 110 MHz. One dielectric relaxation around 106 Hz was observed, which is ascribed to the interfacial polarization mechanism due to the accumulation of “counter-ions” on the boundaries of polypyrrole/solution. The relation between dielectric parameters and volume fractions of the particles shows the linear dependency in the range of investigation. Of interest to be noted, the permittivity of particles calculated from dielectric parameters on the basis of dielectric relaxation spectroscopy by using the Hanai method is much higher than 79.02 (εH2O=79.02,22 °CεH2O=79.02,22 °C). According to the present understanding of the interfacial polarization, the high permittivity of polystyrene-polypyrrole core-shell particles is mainly ascribed to the capture of counterions in polypyrrole matrix with porous morphology and the characteristic conducting mechanism of PPy itself. Moreover, the formation of many dipole moments between Cl− self-doped during the oxidative polymerization of pyrrole and N+ in the backbone of polypyrrole through the electrostatic interaction is also responsible for it.

Dielectric properties of E. coli cell have been re-studied by means of the three-shell spheroidal model, where the three shells correspond to the outer membrane, the periplasmic space and the inner membrane, respectively. With the model, a curve-fitting procedure has been developed to analyze the dielectric spectra. Although E. coli cell has been studied before, its special morphological structure was taken into account more comprehensively than any previous model in the present work. Dielectric properties of various cell components have been estimated from the observed dielectric spectra, especially the permittivity of the outer membrane, which was evaluated quantitatively for the first time. The values of εom were 12 for κom of 0 to 10− 4 S/m and 34 for κom of 10− 3 S/m. The specific capacitance of the inner membrane was 0.6–0.70 μF/cm2. The relative permittivity and the conductivity of the cytoplasm were about 100 and 0.22 S/m, respectively, and the conductivity of the periplasmic space was 2.2–3.2 S/m.

The dielectric spectroscopy of Anabaena 7120 protoplast suspensions has been investigated over the frequency range of 40 Hz–110 MHz. The protoplast suspensions showed a complicated dielectric dispersion consisting of at least four distinct sub-dispersions with the increasing frequencies due to the Maxwell–Wagner interfacial polarization. The double-shell model, in which an equivalent shell of thylakoid was assumed inside the cytoplasm, was adopted to describe the special morphology of the protoplast. Under the assumption that the conductivity of plasmalemma was negligible and the conductivity of the equivalent shell was 0.1 μS/cm, we attempted to estimate the dielectric properties of various protoplast components by fitting theoretical curve to experimental data. The relative permittivity of the plasmalemma εmem was estimated to be 6.5 ± 0.5, and the permittivity of the equivalent shell of thylakoid εthy was estimated to be about 3.2 ± 0.2. The permittivity εcyt and conductivity κcyt of the cytoplasm were estimated to be 60 and 0.88 ± 0.11 mS/cm, respectively. The permittivity εnuc and conductivity κnuc of the nucleoplasmic region were determined to be 100 and 0.13 ± 0.02 mS/cm, respectively.

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 106 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.

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.

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 °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.

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.