Dielectric Relaxation Of Poly Research Articles

Separation of Micro-Brownian Motion and Side-Group Rotational Motion for Poly(N-isopropylacrylamide) in 1,4-Dioxane Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation of poly(N-isopropylacrylamide) (PNiPAM) was investigated in 1,4-dioxane as a low-polarity solvent at a concentration between 0 and 20 wt %, temperature between 40 and −35 °C, and a frequency range between 40 Hz and 1.8 GHz. Results suggest that relaxation due to the molecular motion of PNiPAM has two components: relaxation of side-group rotational motion at ∼100 MHz and micro-Brownian motion of PNiPAM chain at ∼1 MHz at room temperature. These processes are described by the sum of two Cole–Cole equations. Furthermore, the relaxation times of these processes showed distinct temperature dependences, as confirmed by activation energies obtained from the Arrhenius plot. In addition, asymmetric relaxation was observed in the MHz region of PNiPAM in various solvents comprising two individual relaxations. This could explain some fundamental aspects of PNiPAM solution properties and provide a deeper understanding of the molecular dynamics of PNiPAM.

How Confinement Affects the Nucleation, Crystallization, and Dielectric Relaxation of Poly(butylene succinate) and Poly(butylene adipate) Infiltrated within Nanoporous Alumina Templates.

This work describes the successful melt infiltration of poly(butylene succinate) (PBS) and poly(butylene adipate) (PBA) within 70 nm diameter anodic aluminum oxide (AAO) templates. The infiltrated samples were characterized by SEM, Raman, and FTIR spectroscopy. The crystallization behaviors and crystalline structures of both polymers, bulk and confined, were analyzed by differential scanning calorimetry (DSC) and grazing incidence wide angle X-ray scattering (GIWAXS). DSC revealed that a change in the nucleation process occurred from heterogeneous nucleation for bulk samples to homogeneous nucleation for infiltrated PBA and to surface-induced nucleation for infiltrated PBS. GIWAXS results indicate that PBS nanofibers crystallize in the α-phase, as well as their bulk samples. However, PBA nanofibers crystallize just in the β-phase, whereas PBA bulk samples crystallize in a mixture of α- and β-phases. The crystal orientation within the pores was determined, and differences between PBS and PBA were also found. Finally, broadband dielectric spectroscopy was applied to study the segmental dynamics for bulk and infiltrated samples. The glass temperature was found to significantly decrease in the PBS case upon infiltration, while that of PBA remained unchanged. These differences were correlated with the higher affinity of PBS to the AAO walls than PBA, in accordance with their nucleation behavior (surface-induced versus homogeneous nucleation, respectively).

Enthalpy and Dielectric Relaxation of Poly(vinyl methyl ether)

This study investigates the cooperative molecular dynamics of poly(vinyl methyl ether) (PVME) at temperatures above and below the glass transition temperature, Tg, using differential scanning calor...

Enhancement of polar phase and conductivity relaxation in PIL-modified GO/PVDF composites

To investigate the effect of graphene oxide (GO) modified by polymerized ionic liquid (PIL) on the crystallization and dielectric relaxation of poly(vinylidene fluoride) (PVDF), a series of PVDF composites have been prepared using the solution casting method. The ion-dipole interaction between PIL and >CF2 and the π-dipole interaction between GO and >CF2 can induce synergistically the polar phase, and the π-ion interaction between GO and PIL can strengthen the induction effect of the polar phase and decrease the degree of crystallization of PVDF. The electric modulus and conductivity relaxation are employed to analyze the experimental complex dielectric permittivity. In the frequency spectra of complex permittivity of PVDF composites, space charge polarization and conductivity lead to a large value of dielectric permittivity. The temperature dependence of relaxation time of conductivity relaxation accords with the Arrhenius equation. A low degree of crystallization, more ion concentration, and polar phase in PVDF/PIL/GO enhance the movement of the polymer chain segment and charge carriers.

Study of H1 spin lattice relaxation and dielectric relaxation in Poly(propylene glycol) system

Proton NMR spin-lattice relaxation time (T1) and dielectric relaxation time (τ0) have been used to correlate the experimental and calculated values of T1 for Poly (propylene glycol) at 300 K. Also, the contributions of dielectric relaxation time (τ0) of each constituent group of PPG-425 to the effective dielectric relaxation time due to the whole chain of the polymer have been calculated using NMR spin–lattice relaxation time. The H1 NMR data and dielectric data of Poly (propylene glycol) HO [CH(CH3)CH2O]nH with number average molecular weight 425 (n = 7) g mol−1have been used to understand the conformation and basic mechanism of relaxation in polymer in its pure liquid state. Conformational analysis using Hartree-Fock formalism was performed for the polymer of n = 7 and the average bond distances obtained from the computation were used to assign NMR relaxation times to specific subgroups. Free energy and enthalpy of activation associated with methyl and other groups in the chain of PPG molecules have been calculated. BPP (Bloembergen Purcell Pound) model gives better correlation for molecular tumbling motion for PPG-425 in pure liquid state than Kubo & Tomita equation.

Influence of crystallinity on the dielectric relaxations of poly(butylene succinate) and poly[(butylene succinate)-co-(butylene adipate)

Amorphous and semi-crystalline poly(butylene succinate) (PBS) and poly[(butylene succinate)-co-(butylene adipate)] (PBSA) are studied with Differential Scanning Calorimetry and Broadband Dielectric Spectroscopy (BDS). It was shown that 21mol% of butylene adipate group decreases drastically the degree of crystallinity and the size of the crystal lamellae of the PBSA. For the two semi-crystalline polymers, the microstructure is well described by a three-phase model including a small degree of rigid amorphous fraction. Fragility indexes of the main dielectric relaxation are identical for each sample which shows similar segmental dynamics of their amorphous phase. BDS allows detecting complex secondary relaxations in semi-crystalline PBS and PBSA. Local motions are impacted by the microstructure and a new relaxation occurs in more constrained amorphous environments. Correlations between molecular mobility and barrier properties are proposed.

Dielectric Relaxations in Poly(glycidyl phenyl ether): Effects of Microstructure and Cyclic Topology

Cyclic and linear, isoregic and aregic, and isotactic and atactic poly(glycidyl phenyl ether) (PGPE) with molecular weights up to Mw = 5.5 kg/mol are synthesized by ring-opening polymerization of glycidyl phenyl ether. Initiation with tetrabutylammonium fluoride leads to isoregic linear polymers with ∼95% regular linkages, and initiation with B(C6F5)3 and B(C6F5)3/water leads to aregic cyclic and linear polymers, respectively, with ∼50% regular linkages as quantified by 13C NMR. Local, segmental, and chain dynamics in PGPE is investigated by broadband dielectric spectroscopy (10–2–106 Hz). The β-relaxation for linear PGPE is separated into two contributions arising from the motions of side groups and end groups with activation energies of 35.4 and 23.8 kJ/mol, respectively. The β-relaxation process for cyclic PGPE shows the same activation energy as that shown by the side-group contribution in linear PGPE, indicating that topology does not play a key role on the side-group local dynamics. Moreover, cyclic...

Moisture effects on dielectric relaxations of poly (ɛ-caprolactone)/starch biodegradable blends: Local, interfacial and segmental

Poly(ɛ-caprolactone)/starch biocomposites in a wide composition range were studied by thermally stimulated depolarization currents, TSDC, during the drying process following the effect on the dielectric relaxations of moisture loss and blend composition. PCL's cooperative chain mobility is unaffected by the presence of water which is mainly located in the starch inclusions as its segmental relaxation is fixed at 207K. The heterogeneities found in the amorphous phase of neat starch are also observed here as a bimodal α relaxation which shifts to higher temperatures as it dries. The blend plasticization by water molecules also affects the blend secondary relaxations showing how the local motions are hindered by the loss of water which is lower in the blend than in pure starch. The interfacial peak which is intermediate between the α relaxations of the two components is affected by the inclusions change from liquid to glassy state as the blend dries.

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

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

Dielectric relaxation of poly (trimethylene terephthalate) in a broad range of crystallinity

Here we present dielectric relaxation experiments carried out in semicrystalline poly (trimethylene terephthalate) (PTT) samples covering a broad range of crystallinity values. Special attention has been devoted to characterize the two extremes of low and high crystallinity. In particular a high temperature relaxation in the dielectric spectra of highly crystalline PTT, attributed to a Maxwell–Wagner–Sillars process, has been revealed. Moreover, the existence of ordering phenomena during the induction period prior to crystallization has been characterized by dielectric spectroscopy.

Dielectric relaxations of poly(acrylic acid)-graft-poly(ethylene oxide) aqueous solution: Analysis coupled with scaling approach and hydrogen-bonding complex

Dielectric properties of poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) aqueous solution were measured as a function of concentration and temperature over a frequency range of 40 Hz to 110 MHz. After subtracting the contribution of electrode polarization, three relaxation processes were observed at about 20 kHz, 220 kHz, and 4 MHz, and they are named low-, mid- and high-frequency relaxation, respectively. The relaxation parameters of these three relaxations (dielectric increment Δε and relaxation time τ) showed scaling relations with the polyelectrolyte concentration. The mechanisms of the three relaxations were concluded in light of the scaling theory: The relaxations of low- and mid frequency were attributed to the fluctuation of condensed counterions, while the high-frequency relaxation was ascribed to the fluctuation of free counterions. Based on the dielectric measurements of varying temperatures, the thermodynamic parameters (enthalpy change ΔH and entropy change ΔS) of the three relaxations were calculated and these relaxation processes were also discussed from the microscopic thermodynamical view. In addition, the impacts of PEO side chains on the conformation of PAA-g-PEO chains were discussed. PEO side chains greatly strengthen the hydrogen-bonding interactions between PAA-g-PEO chains, resulting in the chains overlapping at a very low concentration and the formation of a hydrogen-bonding complex. Some physicochemical parameters of PAA-g-PEO molecules were calculated, including the overlap concentration, the effective charge of the chain, the friction coefficient, and the diffusion coefficient of hydrogen counterions.

Peculiarities of dielectric relaxation in poly(vinylidene fluoride) with different thermal history

A method of broad-band dielectric relaxation spectroscopy (10−1–107Hz) has been used to study the relaxation processes in the region of melting in two isotropic poly(vinylidene fluoride) films prepared by way of crystallization from melts under different conditions. The intensive relaxation process observed is attributed to manifestation of a space charge formed by extrinsic carriers. The relaxation time and the intensity of the process reduce when the crystallinity increases. This is related to the increase of extrinsic carriers’ mobility in the amorphous areas. It is supposed that at isothermal crystallization there are more chemical defects (end groups, branches, HHTT-type defects) in amorphous areas. Such defects may impede compact chain packing in the amorphous domains and provide conditions for a higher level of mobility of free carriers.

Relaxation Spectrum of Polymer Networks Formed from Butyl Acrylate and Methyl Methacrylate Monomeric Units

The aim of this work is to study the merging of the main α and the secondary β relaxations in poly(butyl acrylate)-i-poly(methyl methacrylate) sequential interpenetrating networks in comparison to net-poly(butyl acrylate)-co-poly(methyl methacrylate) random copolymer networks. In both cases 10% of ethylene glycol dimethacrylate was used as cross-linking agent. The cross-linking density of these networks is high enough to force a certain degree of compatibility of the IPNs, as shown by dynamic-mechanical analysis and thermally stimulated depolarization currents, TSDC. Dielectric relaxation spectroscopy was used to characterize the relaxation behavior in the frequency domain. The strength of the α dielectric relaxation in poly(methyl methacrylate) network is small and the merging with the β relaxation is not apparent in the experimental frequency range. On the contrary, in poly(butyl acrylate) networks it is the strength of the secondary relaxation which is small compared to that of the α relaxation and the...

Dynamic mechanical and dielectric relaxations in poly(di- n-chloroalkylitaconates)

Dielectric and viscoelastic relaxation measurements have been carried out on poly(2-chloroethyl diitaconate) (PDCEI) and poly(3-chloropropyl diitaconate) (PDCPI) between 123 K and temperatures about 293 K above the glass transition temperatures. The two polymers exhibit three peaks, a γ-relaxation in the range from 133 to 193 K (at 1 Hz), a broad β-process, in the range from 193 to 293 K and a third peak observed in mechanical measurements at 323 K (PDCEI) and 293 K (PDCPI) probably corresponding to the α dynamic glass transition phenomena. In dielectric measurements, conductive contributions overlap the α-relaxation precluding the observation of peaks at temperatures above room temperature. The apparent activation energies for the γ-relaxation according to the mechanical and dielectric measurements are close to the values derived from the empirical force field molecular mechanics calculations. A comparison is made between the relaxational data of PDCEI and PDCPI by one hand and poly(di- n-propyl itaconate) (PDPI) and poly(di- n-butyl itaconate) (PDBI) by other. This comparison allows us to conclude the relevant role played by the chlorine atoms not only in the γ relaxations but also in the β relaxations of PDCEI and PDCPI.

Ionic conductivity and dielectric relaxation in poly[(phenyl glycidylether)-co-formaldehyde

Ionic conductivity data and structural relaxation times for poly(phenyl glycidylether)-co-formaldehyde (PPGE) are compared for the supercooled liquid under awide range of temperatures and pressures. Conformance to the fractionalDebye–Stokes–Einstein (fDSE) relation was observed under all conditions. ThefDSE exponent, = 0.81, provides an estimate of the relative magnitude of theactivation volumes for conductivity and dielectric relaxation. The smalleractivation volume for the former suggests less free volume is necessary toaccommodate ion diffusion in the PPGE than that required for dielectricrelaxation. We also fit the combined temperature and pressure dependences ofboth the conductivity and relaxation times to the Avramov equation.

Dielectric relaxation of poly(n-hexyl isocyanate) in concentrated solutions of polybutadiene

We report the dielectric relaxation in a ternary system in which a trace amount of poly(n-hexyl isocyanate) (PHIC) is dissolved in concentrated toluene solutions of polybutadiene (PB). The dielectric response is due to the rod-like PHIC molecules having high dipole moment along its chain contour. Solutions of PB form entanglement networks which retard the reorientation of the PHIC molecules. With increasing concentration (CPB) of PB from 0 to 40wt% the relaxation behaviour changed at a crossover concentration CPB+. In the range below CPB+, the relaxation time τ for reorientation of the PHIC molecules increased on account of the effect of entanglement. However above CPB+, τ decreased and at the same time the relaxation strength decreased with increasing CPB. The crossover concentration CPB+ depended on the molecular weight M of the PHIC, i.e. C+PB=0.13 at M=29,000, and CPB+=0.25 at M=20,000. The decrease of the relaxation strength can be attributed to the reduction of the effective dipole moment due to the restriction of motions of the PHIC chains in entanglement networks of PB chains.

Dielectric relaxations of poly(2-norbornyl methacrylate) and poly(3-methyl-2-norbornyl methacrylate)

Dielectric behaviour of poly(2-norbornyl methacrylate) (P2NBM) and poly(3-methyl-2-norbornyl methacrylate) (P3M2NBM) was studied. The effect of the methyl substituent on the norbornyl ring is to decrease the temperature of the dynamic glass transition about 50K. Moreover, weak secondary relaxations are observed in the two polymers under study. The secondary process of P3M2NBM has been conveniently analysed in terms of the empirical Fuoss–Kirkwood (F–K) equation.

Study of Dielectric Relaxation Processes in Poly(p-phenylene sulfide) Using a Thermally Stimulated Discharge Current Technique

The various dielectric relaxations in poly(p-phenylene sulfide) have been investigated using a thermally stimulated discharge current (TSDC) technique. The TSD current spectra in the temperature range 30 to 250°C was analyzed as a function of poling temperature (100–250°C), poling field (5–18 kV/cm), poling time (1–4 h), specimen thickness (0.8–1.6 mm), heating rate (1–4°C/min.) and storage time (2–720 h). From the variation of the properties of peaks appearing in the TSDC spectra, it is concluded that the peak appearing at around 110°C (β-relaxation) is a dipolar transition due to C–S linkage. Samples poled at higher (Tp > Tg) show a peak at around 170°C (β ′-relaxation), which has been associated with the formation of cross-linked ether linkages. The β ′-relaxation gives all the character of dipolar polarization. The peak at around 210°C (α-peak) has been ascribed to a space charge transition. A rigid amorphous phase (RAP) and unsaturated phenylene groups provide the deep charge trapping centers. The activation energy obtained from the Bucci plot method confirms the respective nature of these peaks. The observed dependence of peak temperature on poling temperature and poling time indicates the presence of continuous distributed relaxation.

Dielectric Relaxation of Poly(n-butyl acrylate)

Dielectric relaxation of poly(n-butyl acrylate) (PBA) was studied over a temperature range from 90 to 300 K. The primary a relaxation was observed around 250 K but the relaxation due to motion of the side ester group as observed for poly(methyl acrylate) (β process) was not observed. Thus the a relaxation was assigned to a merged process where the segmental motions and the rotation of the side group occur cooperatively. A weak secondary (γ) relaxation was observed at 130 K at 1 kHz. The y relaxation was assigned to motion of the alkyl group of the side chain. Dielectric characteristics such as relaxation strength, effective dipole moment, and Arrhenius plot for the a process were compared with those for poly(butyl methacrylate)s reported.

A dielectric study on the local dynamics of miscible polymer blends: poly(2-chlorostyrene)/poly(vinyl methyl ether)

Dielectric relaxation of poly(vinyl methyl ether) (PVME)/poly(2-chlorostyrene) (P2CS) blends with a lower critical solution temperature (LCST) was investigated in the one-phase region over a wide range of temperature. Four distinct dielectrically active processes were observed and identified as α1, α2, β and γ relaxation processes. It was found that the β and γ processes were almost unaffected upon varying the blend composition, while their relaxation intensities were approximately proportional to the PVME content. Furthermore, there exist two peaks (α1, α2) corresponding to the segmental relaxation process of each component. By comparing this with the data obtained by small-angle X-ray scattering and differential scanning calorimetry, the experimental results are discussed in terms of dynamical heterogeneity of miscible polymer blends composed of two polymer components with a large difference in glass transition temperatures.