Dielectric properties of low molecular weight poly(ethylene glycol)s

This paper reports the measured values of dielectric permittivity ε′ and dielectric loss ε″ of ethylene glycol, diethylene glycol and poly(ethylene glycol)s of average molecular weight 200, 300, 400 and 600 g mol⁻¹ in the pure liquid state. The measurements have been carried out in the frequency range 200 MHz to 20 GHz at four different temperatures of 25, 35, 45 and 55 °C. The complex plane plots (ε″ versus ε′) of these molecules are Cole–Cole arcs. The static dielectric constant ε₀, high‐frequency limiting dielectric constant ε_∞, average relaxation time τ₀ and distribution parameter α have been determined from these plots. The value of the Kirkwood correlation factor g and the dielectric rate free energy of activation ΔF have also been evaluated. The dependence of relaxation time on molecular size and viscosity has been discussed. A comparison has also been made with the dielectric behaviour of these molecules in dilute solutions of non‐polar solvents, which were carried out earlier in this laboratory. The influences of intermolecular hydrogen bonding and molecular chain coiling on the dielectric relaxation of these molecules have been recognized. © 2000 Society of Chemical Industry     

The effect of moisture on the dielectric behavior of poly(vinyl acetate)–natural rubber blend

Dynamic dielectric analysis was used to analyze the miscibility of poly(vinyl acetate) and natural rubber and the effect of moisture on the dielectric properties of the polymer blend. Two separate dielectric relaxations were observed within the temperature range studied. The high-temperature relaxation was a result of the glass transition of poly(vinyl acetate), whereas the low-temperature relaxation was attributed to that of natural rubber. The peak temperatures of ε″ of the high-temperature relaxation decreased with increasing aging time, while the magnitudes of the ε″ peaks increased with increasing days of aging. The peak temperatures of ε″ of the low-temperature relaxation stayed constant, while the magnitudes of the ε″ peaks increased with increasing days of aging. This indicates that both polymers are responsible for the sorption of moisture; however, water is an effective plasticizer only for poly(vinyl acetate). Anomalous increases in the magnitudes of ε″, especially in the low frequency sides, of the Argand diagrams were explained by Maxwell–Wagner–Sillar (MWS) polarization at component interfaces. The oscillator strength, relaxation time, and the two distribution parameters, A and B, calculated from the skewed circular are equation, were affected with days of aging.     

Biodegradable blends based on polyvinyl pyrrolidone for insulation purposes

Polyvinyl pyrrolidone/polyvinyl alcohol (PVP/PVA) and polyvinyl pyrrolidone/starch (PVP/St) blends were prepared with different compositions. The compatibility studies indicate that PVP/PVA is compatible while PVP/St is incompatible. The addition of glycerol and glutaraldehyde can improve to some extent the phase separation behavior between PVP and St. The permittivity ε′ and the dielectric loss ε″ were measured in the frequency range 0.01 Hz up to 10 MHz and temperatures from 30 up to 90°C. It is found that the blend ratio (50/50) of both investigated systems is preferable for insulation purposes in comparable with the other blends under investigation. The data of the loss electric modulus M″ was calculated from the dielectric parameters ε′ and ε″and analyzed into three relaxation mechanisms ascribing the cooperative motion of the main and side chains τ₁ (αβ), the side chain motion τ₂ (β) and the segmental motion of the groups attached to the side chains τ₃ (βγ). The activation energy corresponds to the second relaxation process ΔH₂ was calculated using Arrhenius equation and found to be in the range which justifies the presumption of β‐relaxation process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Solvent effects on microwave dielectric relaxation in poly(ethylene glycols)

This paper reports the results of a systematic study of microwave dielectric relaxation times of poly(ethylene glycols), average molecular weight 200–9000, in dilute solutions of benzene at 9·83GHz. These results are compared with the values of relaxation times obtained earlier in carbon tetrachloride solutions. This shows that the average relaxation times τ₀ and the relaxation time corresponding to segmental reorientation τ₁ are influenced by the solvent environment. The variation in chain flexibility in these polymers with the increase in degree of polymerization and formation of intra- and inter-molecular hydrogen bonding in benzene and carbon tetrachloride solutions is discussed with the help of relaxation data. The relaxation time τ₂ corresponding to group rotations has been determined. It is found that the τ₂ value is independent of solvent environment and degree of polymerization, and may be attributed to the rotation of chain −OH end-groups around the C−O bonds in dynamic equilibrium, with the formation of a five-membered ring due to intra-molecular hydrogen bonding at the end of the chain. © 1998 SCI.     

Dielectric relaxation and thermodynamic properties of polyvinylpyrrolidone using time domain reflectometry

Temperature‐dependent values of dielectric permittivity ε′ and dielectric loss ε″ of polyvinylpyrrolidone (PVP, commercialized as PVP K‐60) solution of average molecular weight 160 000 g mol^?1 were measured. The measurements were carried out in the frequency range 10 MHz to 20 GHz using time domain reflectometry at temperatures from 25 to 0 °C. The dielectric spectra can be described by the Davidson‐Cole model. Dielectric parameters such as the static dielectric constant ε₀, the high frequency limiting dielectric constant ε_∞, the relaxation time τ₀ and the distribution parameter β and thermodynamic parameters such as the free energy of activation ΔF_τ, the enthalpy of activation ΔH_τ and the entropy of activation ΔS_τ were determined. The average free energy of activation was found to be in the range 12.55–14.65 KJ mol^?1 and the enthalpy of activation was found to be 6.86 KJ mol^?1. Entropies of activation were found to be positive at all the measured temperature values and these large positive values of entropies reveal a less ordered structure of the PVP solution. The Kirkwood correlation factor g and the dipole moment µ were also determined for PVP solution. The results were compared with the results of the PVP‐water system studied previously. Copyright © 2011 Society of Chemical Industry     

Dielectric behaviour and relaxation in poly(propylene glycol)–water mixtures studied by time domain reflectometry

Dielectric behaviour of poly(propylene glycol) (PPG) of number‐average molecular weight 2000 g mol^?1 and binary mixtures of PPG with water (PPG–W) of various concentrations were carried out in the frequency range 10 MHz to 4 GHz at 25 °C. The dielectric dispersion and absorption curves related to the orientational motion of these molecules in the binary mixtures are described by a single relaxation time using Debye's model. The values of static dielectric constant ε_o, high frequency limiting dielectric constant ε_∞, and dielectric relaxation time τ_o were determined for PPG and PPG–W mixtures. The values of the dielectric parameters were used to explore the nature of homogeneous and heterogeneous dynamic networks formed through hydrogen bonding in the binary mixtures of PPG and water molecules with concentration variation. The dielectric studies of PPG molecules were also carried out in the same frequency range at four temperatures, namely 25, 35, 45 and 55 °C. The temperature‐dependent relaxation times were used to evaluate the thermodynamical parameters for the dielectric relaxation processes. The dielectric relaxation free energy of activation ΔF_τ for PPG molecules was found in the range ～4.5 to 4.7 kcal mol^?1, which corresponds to the activation energy needed for the breakage of hydrogen bonds. Furthermore, the large negative value of the entropy ΔS_τ of PPG molecules confirms that the configuration involved in dipolar orientation has an activated state, which is more ordered than in the normal state. Copyright © 2004 Society of Chemical Industry     

The variation of the dielectric constant and loss index with temperature and draw ratio in α‐PVDF

In this study, the effect of measurement temperature and uniaxial drawing on the real (dielectric constant, ε′) and imaginary (loss index, ε″) parts of the complex dielectric constant of α‐crystalline phase poly(vinylidene fluoride) (PVDF) was investigated. The samples having different draw ratios (λ) were obtained by drawing the PVDF film at constant speed and temperature. The dielectric measurements were performed in the frequency range of 100 Hz–1 MHz and in the temperature range of 80–400 K. Although ε′ and ε″ were not affected by the orientation process during the β‐relaxation transition, it was observed that there were systematical variations for the α‐relaxation transition. ε′ and ε″ showed different behaviors depending on the draw ratio at different temperatures. Especially, ε″ was more affected by the orientation process at 380 K. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dielectric relaxation of binary mixtures of alcohols with acrylic esters

A dielectric relaxation study on alcohol–acrylic ester binary mixtures has been carried out at different concentrations using time domain reflectometry (TDR). The least‐squares fit method has been used to obtain the dielectric parameters (the static dielectric constant ?₀ and the relaxation time τ). By using these parameters, the Bruggeman factor, the Kirkwood correlation factor, and excess inverse relaxation time were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The ?₀ and τ values decreased with an increase in the percent of acrylic ester in alcohol for all the systems. The value of t increased with an increase in chain length of both the alcohol and acrylic ester, whereas the reverse trend is observed for ?₀. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(vinyl pyrrolidone)–poly(ethylene glycol)s in non‐polar solvent

Dielectric relaxation study of binary mixtures of poly(vinyl pyrrolidone) (PVP) (M_w = 40 000 g mol^?1) and poly(ethylene glycol)s (PEGs) (M_n = 200, 400 and 600 g mol^?1) with concentration variation was carried out in dilute solutions of benzene at 10.1 GHz and 35 °C. The average relaxation time τ_o, corresponding to segmental motion τ₁ and group rotations τ₂ was determined for PVP–PEGs mixtures. A comparison of these mixtures relaxation times was made with the relaxation times of PEGs in benzene solvent. The evaluated τ_o values of PVP–PEGs mixtures in benzene solution are assigned to the reorientation of PEG molecules. It has been observed that the τ_o value of PVP–PEG200 mixtures increases with increasing concentration of PVP but their values are small in comparison with the τ_o value of PEG200 molecules. In the case of PVP–PEG400 and PVP–PEG600 mixtures, the evaluated values of τ_o are greater than the corresponding τ_o values of PEG400 and PEG600 molecules in benzene solvent. The variation in τ_o values in these systems has been discussed by considering the stretching effect in the PEGs molecular chains in PVP–PEGs mixtures in benzene solutions. The high value of distribution parameter α (≈0.4 to 0.7) suggests that in these mixtures there is a large contribution of segmental motion and group rotations to the relaxation processes. The nature of the formation of hydrogen‐bonded PVP–PEG complex heterogeneous network due to hydrogen bonding between carbonyl groups of PVP monomer units and terminal hydroxyl groups of PEGs is discussed. Furthermore, the elongation behaviour of PVP–PEG complex networks in benzene solvent and the molecular dynamics in the mixture due to breaking and reforming of hydrogen bonds has been explored by comparing the evaluated relaxation times and the Kirkwood correlation factor of pure PEG molecules for their possible use in drug control release systems. The relaxation times of these mixtures are independent of their viscosity, but the elongation of the mixture network is influenced by the PEG chain length and the number of hydroxyl groups in comparison with the number of carbonyl groups in the mixtures. Copyright © 2003 Society of Chemical Industry     

Dielectric properties of poly(vinyl chloride) in tetrahydrofuran and cyclohexanone

The dielectric absorption and dispersion of poly(vinyl chloride), M M_v = 49 000, in THF and in cyclohexanone have been studied over a frequency range of 120 kHz to 11·0 MHz, at temperatures from ?22·5 to 35°C, and at concentrations ranging from 4 to 12·0(w/v)% PVC/THF and from 2 to 8·0(w/v)% PVC/cyclohexanone. The viscosities of the two systems have also been measured at temperatures from 20 to 50°C. A single relaxation time was found (β = 0·8–1·0), which indicates that relaxation occurs by segmental rotation. The dielectric and viscous activation energies have been calculated. The dipole moment associated with the relaxation process has also been calculated. The relaxation time, dielectric and viscous activation energies and the dipole moment were found to be dependent on the type of solvent. The dipole moment also showed a molecular weight dependence. The influence of the concentration and temperature on the apparent dipole moment and on the relaxation time is discussed.     

Dielectric relaxation and Poole–Frenkel conduction in poly(vinyl chloride) blends with bisphenol A/Egyptian corncob resin

The dielectric constant (ε′), dielectric loss index (ε″), direct-current conductivity, and current–voltage (I–V) characteristics of pure poly(vinyl chloride) (PVC) and blends of PVC and bisphenol A/Egyptian corncobs (BCC) were investigated at different temperatures. The relaxation processes for PVC and its blends revealed that PVC and BCC had an incompatible phase. PVC blends with 5 wt % BCC exhibited a peculiar I–V behavior. Both ε′ and ε″ were used to study miscibility and phase behavior in blends of PVC. The activation energies of all PVC samples were calculated. At higher voltages, the conduction mechanism could be identified as the Poole–Frenkel type. In addition, the ionic groups of BCC could enhance the PVC conductivity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dielectric investigation of isotropic and anisotropic solutions of hydroxypropyl cellulose in dioxan

The dielectric behaviour of hydroxypropyl cellulose in dioxan has been studied at 10–50°C over a range of concentration of 10–55 wt% to include the isotropic and anisotropic phases. The study showed that the loss maximum ε″_max magnitude of polarization ε₀ ? ε_∞ relaxation time 1/2πf_m degree of broadening of the absorption curves 1–h or α, and the mean-square dipole moment 〈gμ²〉, steadily increase with concentration up to 42 wt%, above which a rapid decrease takes place. This indicates that the isotropic solution transforms to an anisotropic solution with a smaller mean dipole moment. The critical concentration is realized to be temperature invariant. This was evidenced by measuring the refractive index of solutions covering the same concentration and temperature ranges.     

Dielectric dispersion and AC conductivity of acrylonitrile butadiene rubber‐poly(vinyl chloride)/graphite composite

Dielectric properties and ac electrical conductivity of Acrylonitrile Butadiene Rubber‐poly(vinyl chloride)/Graphite Composite were studied at different frequencies (10²?10⁶ Hz) in the temperature range (298–423 K). The results show that the dielectric constant (ε′), dielectric loss (ε″), ac electrical conductivity (σ_ac) and, the electric modulus are strongly dependent on the frequency and temperature. The dielectric constant ε′ increases with temperature and decreases with frequency, whereas the dielectric loss ε″ displays a broad maximum peak whose position shifts with temperature to a higher frequency region. Cole–Cole diagrams have been used to investigate the frequency dependence of the complex impedance at different temperature and graphite loading. Interfacial or Maxwell‐Wagner‐Sillars relaxation process was revealed in the frequency range and temperature interval of the measurements, which was found to follow the Havriliak–Negami approach for the distribution of relaxation times. At constant temperature, the frequency dependence of ac conductivity was found to fit with the established equation σ_ac(ω) = Aω^s quite well. The values of S for the investigated samples lie between 0.88 and 0.11. The conduction mechanism of ac conduction was discussed by comparing the behavior of the frequency exponent S(T) with different theoretical models. It was found that the correlated barrier hopping (C.B.H.) is the dominant conduction mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dielectric relaxation spectra of chemically treated woods

The changes in the dielectric properties of absolutely dried Sitka spruce (Picea sitchensis Carr.) wood caused by chemical treatments were investigated. Eight kinds of chemical treatments with various levels of weight percentage gain (WPG) were performed. Through the application of the Cole–Cole circular arc law to the results of the dielectric measurements in the frequency range of 1 kHz to 1 MHz at ?60°C, the relaxation spectrum was calculated. The relaxation magnitude (ε₀ ? ε_∞) was reduced by formalization, acetylation, propylene oxide, and phenol–formaldehyde resin treatments, in which chemical reactions occurred between the OH groups in the cell wall and the added reagents. On the other hand, the generalized relaxation time (τ_m) decreased with increasing WPG, except for acetylation, for which τ_m decreased up to a WPG level of 20% and then increased. In poly(ethylene glycol) impregnation, (ε₀ ? ε_∞) decreased with increasing WPG up to about 50% and then increased, whereas τ_m linearly decreased with increasing WPG. No significant changes in these parameters were recognized for the wood methyl methacrylate composite and heat treatment. With the steam treatment, τ_m increased. The distribution of the relaxation times was broad in acetylation and narrow in propylene oxide treatment and poly(ethylene glycol) impregnation. However, it remained almost unchanged in the other treatments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 37–43, 2005     

Microwave dielectric relaxation in binary mixtures of poly(ethylene glycols) in solution

The average relaxation time τ₀, relaxation times corresponding to segmental motion τ₁ and group rotations τ₂, of a series of binary mixtures of poly(ethylene glycols) (PEG 200+PEG 300, PEG 400+PEG 600, PEG 1500+PEG 4000, PEG 6000+PEG 9000, PEG 200+PEG 1500, PEG 300+PEG 4000, PEG 400+PEG 6000 and PEG 600+PEG 9000) have been carried out in dilute solutions of benzene and carbon tetrachloride at 9·83GHz. The effect on chain flexibility due to inter- and intra-molecular association in these binary mixtures is discussed by comparing relaxation times of these mixtures with their individual relaxation times in solution. It is inferred that the extent of hydrogen bonding in different binary mixtures is not similar and is influenced by solvent environment, but there is correlation between τ₀ and τ₁ values in all these binary mixtures, which may be because of hydrogen bonding. The observed τ₂ values in all these mixtures suggests that the chain-ends remain excluded from the intermolecular association and τ₂ is independent of the polymer constituents of the mixture and solvent. It is also equal to the τ₂ values of the individual polymers. © 1998 SCI.     

Dielectric analysis of α‐relaxation process of chlorinated poly(vinyl chloride) stabilized with nitro‐phenyl maleimide

Nitro‐phenyl maleimide (NPM), is the organic stabilizer for poly (vinyl chloride) (PVC), has been investigated as thermal plasticization for rigid chlorinated poly (vinyl chloride) (CPVC). Dielectric relaxation of CPVC stabilized with 10 wt% of NPM has been studied in temperature and frequency ranges of 300–450 K and 10 kHz–1 MHz, respectively. An analysis of the dielectric constant, ε′ and dielectric loss index, ε″, was performed assuming a plasticization effect of NPM molecules. The plasticization effect of NPM molecules was confirmed by the behavior of the dielectric modulus M′ and M″ spectra. A clear dielectric α‐relaxation process has been obtained in the studied temperature range. The results showed that NPM reduce the glass transition temperature, T_g, of CPVC by about 20 K. This effect has been assigned to the plasticization effect of NPM. At lower temperatures, dielectric modulus spectra reveal that there is a role of the effect of the electrode polarization in the relaxation process. The behavior AC conductivity, σ_ac, indicated that the conduction mechanism in all CPVC samples is hopping type conduction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol)s of varying molecular weight in dilute solution

Molecular dynamics of binary mixtures of poly(propylene glycol) (PPG) and poly(ethylene glycol)s (PEGs) of varying molecular weight due to molecular interactions, chain coiling and elongation in dilute solution under various conditions, ie varying number of monomer units of PEG, method of mixing of polymers and solvent environment, has been explored using microwave dielectric relaxation times. The average relaxation time τ_o, relaxation time corresponding to segmental motion τ₁ and group rotations τ₂, of a series of binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol) of varying molecular weight (ie PPG 2000 + PEG 200, PPG 2000 + PEG 300, PPG 2000 + PEG 400, and PPG 2000 + PEG 600 mixed by equal volume in the pure liquid states, and PPG 2000 + PEG 1500, PPG 2000 + PEG 4000 and PPG 2000 + PEG 6000 mixed equal weights in solvent) have been determined in dilute solution in benzene and carbon tetrachloride at 10.10 GHz and 35 °C. A comparison of the results of these binary systems of highly associating molecules shows that the molecular dynamics corresponding to rotation of a molecule as a whole and segmental motion in dilute solutions are governed by the solvent density when the solutes are mixed in their pure liquid state. Furthermore, the molecular motion is independent of solvent environment when the polymers are added separately in the solvent for the preparation of binary mixtures. It has also been observed that there is a systematic elongation of the dynamic network of the species formed during mixing of pure liquid polymers in lighter environment of solvent with increasing PEG monomer units, while the elongation behaviour of the same species in the heavier environment of carbon tetrachloride solvent is in contrast to the elongation behaviour of the polymeric species formed in pure PEG. The role of rotating methyl side‐groups in the PPG molecular chain has been discussed in term of the breaking and reforming of hydrogen bonds in complex polymeric species for the segmental motion. In all these mixtures, the relaxation time corresponding to group rotations is independent of the solvent environment and constituents of the binary mixtures. The effect of chain flexibility and coiling in these binary mixtures is discussed by comparing the relaxation times of the mixtures with their individual relaxation times in dilute solutions measured earlier in this laboratory. © 2001 Society of Chemical Industry     

Electrode polarization for nylon 1010 with dielectric relaxation spectroscopy

Electrode polarization arising from charge carriers accumulating at the interface between an electrode and nylon 1010 was investigated with dielectric relaxation spectroscopy. In the frequency spectra of nylon 1010, the dielectric permittivity showed high values in the region of low frequencies and high temperatures. With the Havriliak–Negami function used to fit the experimental spectra, the result revealed that the high values originated from electrode polarization and direct‐current conductivity. For electrode polarization, the dielectric strength, independent of the temperature, was about 1150, and the temperature dependence of the relaxation time followed the Vogel–Tammann–Fulcher equation. Fitting with the Vogel–Tammann–Fulcher equation, the parameters τ₀ = 1.33 × 10^?10 s and T₀ = 303.2 K were proposed (where τ₀ is the relaxation time at a very high temperature and T₀ is the temperature at which the relaxation time becomes extremely large), and they suggested that the motion of the polymeric chains was one of the factors leading to charge‐carrier transport at temperatures higher than the glass‐transition temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3590–3596, 2006     

Dielectric investigation of isotropic and anisotropic solutions of cellulose acetate in dioxane

The dielectric and optical characteristics of a sample of cellulose acetate (DS = 2.45) in dioxane solutions were studied at 10–50°C of concentration 10–50 wt% to include both isotropic and anisotropic phases. The study showed that the loss maximum, ε_max″, magnitude of polarization, (ε₀ ? ε_∞), static dielectric constant, ε₀, time of relation, (2πf_m)^?1, and refractive index, n_D, steadily increase with concentration up to the critical concentration (41 wt%) and then decrease. The mean-square dipole moment, 〈gμ²〉, decreases steadily up to the critical concentration then remains nearly constant, indicating that the isotropic solution changes to anisotropic, with smaller mean-square dipole moment. Comparison between the results of cellulose acetate (CA) and those of hydroxypropyl cellulose (HPC) reveals that, at the critical concentration in dioxane, the cholesteric structure of HPC possesses a greater mean-square dipole moment with higher temperature coefficient than does CA. The activation energy of the relaxation process for hydroxypropyl cellulose is higher, indicating a greater intrachain interaction compared with cellulose acetate.     

Studies on syntheses and permeabilities of special polymer membranes. X. Effects of conditions of membrane preparation on permeation characteristics of cellulose acetate membranes in separation of aqueous polymer solutions

The effects of casting solvents, dissolution temperature of casting solution, and pH and temperature of gelation solution, etc. on the permeation characteristics of cellulose acetate membranes in the separation of polymers from their aqueous solutions were investigated, using aqueous solutions of poly(ethylene glycol) and poly(vinyl alcohol) as feed. The permeation characteristics were influenced significantly by the conditions of membrane preparation and of the permeation. It was found that a concentration polarization at the membrane surface occurred with poly(vinyl alcohol) molecules, but it was very small with poly(ethylene glycol). The above results were discussed in detail from points of view of structure of the resulting membranes and the interactions between the solvent, the solute in the feed and the cellulose acetate molecules.