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We report the dielectric study of dynamical heterogeneity in miscible polymer blends composed of four kinds of polyethers, i.e., poly(butylene oxide) (PBO), poly(isopropylglycidyl ether) (PiPGE), poly( n -butylglycidyl ether) (PnBGE), and poly( t -butylglycidyl ether) (PtBGE). All polyethers exhibit both the dielectric normal mode relaxations due to fluctuation of the end-to-end vector and the segmental mode due to local motions. In blends composed of polyethers, the loss curves for the segmental modes are unimodal but are asymmetrical when the composition becomes asymmetrical, namely 75/25 and 25/75. The asymmetrical loss curve indicates that the loss curve consists of the fast and slow modes. We have resolved the loss curves into the fast- and slow modes by curve fitting assuming that the segmental modes are composed of two e ″ curves. Thus we have estimated the separation of the fast and slow modes. The separation is approximately proportional to the difference of the glass transition temperatures of the components.

We studied viscoelastic and dielectric relaxation behavior of poly(vinyl acetate)/poly(ethylene oxide) (PVAc/PEO) blends in the miscible state. Especially for the viscoelastic measurements, we used highly asymmetric molecular weight MW combinations to examine the component dynamics separately. Time–temperature superposition principle did not hold since the two components have different shift factors (aT). We determined the aT of both components in the blends for the terminal relaxation modes. Concerning the dielectric relaxation, we observed single α-relaxation peak and found that the α-relaxation mainly reflected the segmental motion of PVAc in the blends. The dielectric and viscoelastic aT of the PVAc component showed almost the same temperature dependence compared at the same composition. From these aT data, we determined effective glass transition temperatures (Tg,eff) as a function of blend composition for both components. The results were compared with the literature data for a similar miscible blend, poly(methyl methacrylate) (PMMA)/PEO [T.R. Lutz, Y. He, M.D. Ediger, H. Cao, G.Lin, A.A. Jones, Macromolecules 36 (2003) 1724]. The Tg,eff’s of PEO in the two blend systems were almost the same at any compositions even though the blend partners have very different glass transition temperatures Tg’s: 311 K for PVAc and 405 K for PMMA. If we use the Lodge–McLeish (LM) model to explain the similar Tg,eff’s of PEO in both blends, the self-concentration of PEO should be dependent on the blend partner. This suggests the necessity to take into account the effect of the inter-molecular interaction in the LM model.

We investigated the dielectric normal mode relaxation in dilute and semidilute solutions of poly(propylene oxide)(PPO) and poly(butylene oxide)(PBO) in benzene which is a good solvent for PPO but a marginal solvent for PBO. The results indicate that the normal mode relaxation times τn in dilute solutions of PPO and PBO are proportional to [η]M in agreement with the Rouse-Zimm theory where [η] and M denotes the intrinsic viscosity and the molecular weight, respectively. With increasing concentration C, τn increases in proportion to C[η]. The dynamic crossover concentration between the dilute and semidilute regimes is about four times higher than the static crossover concentration C*. The relaxation strength Δe divided by C decreases with increasing concentration indicating that the mean square end-to-end distance decreases on account of the screening of the excluded volume effect. The concentration dependence of agrees approximately with the scaling theory.

We report dielectric relaxation behavior in blends of sodium montmorillonite particles (MM) with a series of polymers (i.e., polyisoprene (PI), poly(propylene glycol) (PPG), and poly(butylene oxide) (PBO)). These polymers are known to exhibit the dielectric normal mode due to the fluctuation of the end-to-end vector as well as the segmental mode due to local, segmental fluctuations. The data indicate that all blend systems exhibit an additional relaxation process at a temperature region below the glass transition temperature, T g , of the pure polymer component. The intensity of the new relaxation process increases with the content of MM and hence the relaxation process can be assigned to the segmental motion of the chains intercalated in the interlayers of MM. On the other hand, the relaxation time of the normal mode reflecting the fluctuation of the end-to-end vector is the same as the neat polymers but the intensity of the relaxation process increases due to enhancement of the internal electric field by MM.

Dynamic heterogeneity in miscible blends was investigated by the use of dielectric relaxation spectroscopy for blends composed of poly(vinylethylene) (PVE) and various polyethers, i.e., poly(butylene oxide) (PBO), poly(isopropyl glycidyl ether) (PiPGE), poly(n-butyl glycidyl ether) (PnBGE), and poly(tert-butyl glycidyl ether) (PtBGE). All polyethers are type AB polymers and exhibit both the dielectric normal- and segmental-mode relaxations, but PVE exhibits only the segmental relaxation. The data indicate that the loss curves for the segmental relaxation of PVE/PBO blends are bimodal in the range of PBO content less than 0.25. Since the dielectric relaxation strength of PBO is much higher than that of PVE, unimodal loss curves are seen at high PBO content. The effective glass transition temperatures for the fast and slow modes estimated with the Lodge−McLeish model agree fairly well with the temperatures at which segmental relaxation times become ca. 100 s. The ratio of the relaxation times for the normal...

We studied the dielectric relaxation behavior of low mass compounds (LMC) mixed in polystyrene (PS). Specifically, LMCs that are used are alkyl-cyanobenzene (nCBz, n = 0), alkyl-cyanobiphenyl (nCB, n = 0, 1, 3, 5, and 7), and alkyl-cyanoterphenyl (nCT, n = 5), where n represents the number of carbon atoms of the normal alkyl groups of the LMCs. Owing to a much larger dipole moment of the cyano group than that of PS, only motions of the LMCs were observed. In a blend of 5CT (5 wt %)/PS, single relaxation process designated as α was observed. On the other hand, in nCB (5 wt %)/PS, partially overlapped two relaxation processes (α and β) were observed in the order of decreasing temperature. We assigned the α process to cooperative motions between the LMC molecules and the PS segments, and the β process to spatially restricted motions of the LMC molecules in the glassy state. In 0CBz (8 wt %)/PS, the α and β processes were observed in distinct temperature regions and the intensity of the α peak was comparable to that of pure PS, indicating that the 0CBz molecules do not move cooperatively with the PS segments. We conclude the existence of two critical sizes (I and II) of LMC in relation to cooperativity: when an LMC molecule is smaller than the size-I, the motions of the LMCs and PS segments decouple each other, but above the size-I, they become cooperative. Above the size-II, the spatially restricted motion (β-process) of LMC does not occur. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 967–974, 2006

Dielectric measurements were carried out on undiluted poly(isopropyl glycidyl ether) (PiPGE), poly(n-butyl glycidyl ether) (PnBGE), and poly(tert-butyl glycidyl ether) (PtBGE) which have dipoles aligned parallel (type A) and perpendicular (type B) to the chain contour and the dipoles residing on the flexible side group (type C). These polyethers exhibited three dielectric relaxations designated as αn, αs, and β. The αn relaxation is due to the normal mode relaxation. The primary αs relaxation is assigned to local segmental motions coupled with rotation of the side group. The β relaxation can be assigned to both twisting motions of the main chain and libration of the side groups of a small amplitude. Independent full rotation of the side groups was not observed below Tg. The relaxation strengths and dipole moments associated with the αn, αs, and β processes have been estimated. In PiPGE and PtBGE, the temperature dependence of the loss maximum frequency fms for the αs relaxation was much steeper than that ...

Dielectric measurements were carried out on undiluted poly(butylene oxide) (PBO) with various molecular weights. The dielectric normal mode relaxation due to fluctuation of the end-to-end vector and the segmental relaxation due to local motions were observed. The relaxation time τn for the normal mode and τs for the segmental mode conformed to the Vogel−Fulcher equation, and the ratio of τn/τs did not depend on temperature. From the relaxation strengths for the normal and segmental modes, the parallel and perpendicular components of the dipole moment were determined. With the aid of the literature data of the end-to end distance, the dipole moment per unit contour length of PBO chains was also determined. It was found that the M dependence of τn changed around the characteristic molecular weight Mc (=6000), i.e., in the range of M Mc τn is proportional to M3.4. The relationship between the segmental dynamics and chain dynamics is discussed.

We report the dielectric properties of poly(styrene oxide)s (PSO) in bulk and concentrated solution states. Since the structure of PSO is asymmetric along the backbone, the repeat unit of PSO is expected to possess the non-zero component of the dipole moment pA parallel to the chain contour as well as the perpendicular component pB. The former and latter cause the dielectric normal mode and segmental mode relaxations, respectively. Contrary to the above mentioned expectation the temperature dependence of e″ exhibits only the primary (α) relaxation and weak secondary relaxation (β) in the glassy state. No loss peak due to the normal mode relaxation was observed in the frequency region expected from the viscoelastic terminal relaxation in bulk and toluene solutions. The dielectric behaviours of the α relaxation in the bulk state were analyzed in detail and the parameters of the Vogel–Fulcher and the Havriliak–Negami equations were determined. The Kirkwood correlation factor was determined to be 0.36. The 13C NMR spectra indicate that the present PSO samples contain about 2% head-to-head linkages. This cannot be the origin of the disappearance of the normal mode. We conclude that pA of PSO is too small to be detected. The pA calculated with molecular orbital methods supports this conclusion.

The specific heat capacities Cp of blends consisting of cis-polyisoprene (PI) and poly-(vinylethylene) (PVE) were measured in the temperature range from 80 to 320 K by using an adiabatic calorimeter. The configurational heat capacities C conf of blends around the glass transition temperature Tg have been determined by subtracting the vibrational heat capacities estimated with the Einstein and Debye theories. The C conf vs temperature T curves of the blends exhibit double sigmoidal increase at two glass transition temperatures T g1 and T g2 and can be resolved into two empirical sigmoidal curves. For each sigmoidal curve with the index j = 1 or 2, we have also determined the magnitude of the jump ACj and the broadness parameter Bj of the sigmoidal curves. The dielectric relaxation spectrum for the primary process of PI/PVE blends is known to be bimodal due to dynamical heterogeneity. The relationship between the bimodal dielectric segmental relaxation and the double glass transition processes has been analyzed.

We investigated the segmental and terminal relaxation dynamics of a well-characterized disordered diblock copolymer, poly(isoprene-b-vinyl ethylene) (PI-PVE), and miscible blends of polyisoprene (PI)/poly(vinyl ethylene) (PVE), using dielectric and viscoelastic spectroscopies. Generally, the concentration fluctuation (CF) amplitude of a disordered diblock copolymer is smaller than that of the miscible blend, especially in a length scale longer than the size of the whole block chain. To test whether the difference in the CF amplitudes causes the difference in the segmental relaxation spectra, we compared the shape of the dielectric loss curves between PI-PVE and PI/PVE with the same composition (PI/PVE ratio = 17:83). However, no appreciable difference was observed, indicating that the CF amplitudes in PI-PVE and PI/PVE are not so different in the length scale of the segmental motions. We also examined the effect of distinct friction coefficients of the PI and PVE chains on the terminal relaxation dynamics by comparisons of the viscoelastic and dielectric normal mode relaxations in PI-PVE. The former probes the whole chain motion and the latter probes motions of the PI block. Shift factors (aT) for the viscoelastic and dielectric relaxations were compared. The dielectric normal mode aT was found to have weaker temperature dependence than the viscoelastic aT, which indicates that the friction for the PI block chain is lower than the average friction for the PI-PVE chain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4084–4094, 2004

Phase behavior and dynamics in blends of a liquid crystal 4-cyano-4‘-n-pentylbiphenyl (5CB) and polystyrene(PS) were investigated by using dielectric spectroscopy. The blends exhibit phase separation of a UCST type. Below the phase-separation temperature, the blends separate into the isotropic PS-rich and 5CB-rich phases. With decreasing temperature the 5CB-rich phase transforms into the nematic liquid crystalline state and subsequently into the regular crystalline states. The nematic phase supercools about 30 K below the nematic-to-crystal transition point TNC. Optical micrographs of blends indicate that spherical 5CB-rich domains are dispersed in the matrix of PS-rich phase even at the 5CB content of 80%. A strong dielectric relaxation due to rotation of the 5CB molecules in the isotropic PS-rich phase has been termed α. The α process exhibits complex temperature dependence due to the changes in the composition and morphology with temperature. Although the 5CB-rich phase crystallizes mostly at low tempe...

We investigated the dielectric normal mode relaxation on diblock copolymers poly(isoprene-block-butadiene) (I-B) with several polyisoprene (PI)/polybutadiene (PB) compositions. Through the dielectric measurements on I-B, we can obtain information about the dynamics of the PI subchain since the PI block is labeled with type-A dipole but PB is not. At the same time, we carried out viscoelastic measurements on the same I-B samples to obtain information of the whole chain motion, especially the longest relaxation times and the plateau moduli. From these viscoelastic and dielectric data, we can directly compare the relaxation spectra of subchains with those predicted by the tube model. From such comparison, we have found that the end part of the chain relaxes faster than the theoretical prediction suggesting extra relaxation mechanisms other than reptation in the dynamics of chain ends.

We investigated the dielectric relaxation in blends of 4-n-pentyl-4’-cyanobiphenyl (5CB) and polystyrene (PS) in order to examine the size effect of low mass molecules on the cooperativity of local dynamics. To obtain the dielectric data in the isotropic state, the phase diagram was produced. The temperature (T) dependence of the dielectric loss factor e” of PS/5CB blends containing 20 to 30 wt% of 5CB exhibited a bimodal peak near the calorimetric glass transition temperature Tg. The bimodal peak was resolved into two peaks termed α and β. The α process locates above Tg and can be assigned to cooperative motions of the PS segments and the 5CB molecules. The β process is responsible to independent reorientation of the 5CB molecules in the glassy PS matrix. The α and β loss peaks tend to merge with increasing T. This behavior contrasts to the dielectric behavior of the PS/toluene system which exhibits loss peaks due to segmental motions of PS and rotation of the toluene molecules in well separated temperature regions. The toluene molecule has a size of ca. 1/3 of the 5CB molecule and does not move cooperatively with PS but the 5CB molecule does. From the intensity of the α and β peaks, the fraction of the 5CB molecules moving cooperatively with PS has been estimated to be 0.25 and 0.63 for the blends containing 30 and 20 wt% of 5CB, respectively.

We investigated the thermal and dielectric behavior of blends consisting of semicrystalline poly(l-lactic acid) (L-87) and amorphous poly(dl-lactic acid) (DL-74 and DL-7). Two series of blends L-87/DL-74 coded as B1 and L-87/DL-7 coded as B2 were used where the code number indicates molecular weight Mw in kg/mol. The DSC thermograms of quenched blends exhibited a single glass transition at about 326 K followed by the exothermic peak due to crystallization of L-87. The relatively sharp glass transition indicates that both components are miscible in the molten state. The degree of crystallinity χ was determined from the heat of fusion. Three dielectric loss peaks were observed for B2. They are termed αn, αs, and β as reported previously [Macromolecules 2003, 36, 210] and are assigned to the normal mode relaxation of DL-PLA dissolved in the amorphous region, the segmental mode process, and local twisting motions of the main chains, respectively. The dielectric relaxation time for the αn relaxation was almost...

Dielectric study was performed on the polyisoprene (PI)/poly(vinyl ethylene) (PVE) miscible blends. We observed the end-to-end vector fluctuation dynamics (normal mode) of PI as well as the two α-relaxation processes corresponding to the segmental motions of PVE and PI. Among these three relaxation modes, the normal mode relaxation behavior was examined in detail. Since this relaxation reflects the dynamics of the length corresponding to the end-to-end distance of PI chain, comparison of the relaxation times for the normal mode and α-processes gives the information about the length scale of the two α-relaxation modes. We estimated the relevant length scales for the segmental motions in the blend and compared them with a single cooperative volume model and a dual length scale model. As a result, the latter model was found to describe better the features of the segmental dynamics in PI/PVE blends.

The effect of the solvent quality on local concentration fluctuation was studied for concentrated solutions of polystyrene (PS) in toluene (Tol), ethylbenzene (EtBz), n-propylbenzene (PrBz), and n-butylbenzene (BuBz) by using dielectric spectroscopy. The exponents of the Mark−Houwink−Sakurada equation of those solutions indicate that the solvent quality deteriorates in the order of Tol, EtBz, PrBz, and BuBz. Three dielectric relaxations designated as α, β, and γ are observed in the temperature dependence curves of the dielectric loss in the order of decreasing temperature. According to our previous study on PS/Tol solution, the α, β, and γ relaxations have been assigned to local segmental motions of PS, rotation of the solvent molecules, and the secondary relaxation in the glassy state, respectively. The half-width of the dielectric loss curve Λα for the α relaxation of PS/Tol solutions is independent of temperature, but the values of Λα for solutions in EtBz, PrBz, and BuBz increase with decreasing tempe...

Fractionated samples of d , l -poly(lactic acid) (PLA) were prepared and the dielectric normal mode relaxation was studied for dilute and semi-dilute solutions of the PLA in a good solvent benzene. Results indicate that in the dilute regime the normal mode relaxation time is proportional to [η]Mw in agreement with the Rouse–Zimm theory, where [η] and Mw denote the intrinsic viscosity and weight average molecular weight, respectively. The dielectric relaxation strength which is proportional to the mean square end-to-end distance 〈r2〉 increases with increasing Mw with the power of 2ν, where ν is the excluded volume parameter determined from [η]. The relaxation time in the semi-dilute regime increases with increasing concentration C due to increases of the entanglement density and the friction coefficient. The relaxation time corrected to the iso-friction state agrees approximately with the dynamic scaling theories. The relaxation strength decreases with increasing concentration indicating that 〈r2〉 decreases on account of the screening of the excluded volume effect. The concentration dependence of 〈r2〉 agrees approximately with the scaling theory proposed by Daoud and Jannink.

We report the dielectric and viscoelastic relaxations in undiluted amorphous poly(d,l-lactic acid) (PLA). Three dielectric relaxations designated as αn, αs, and β are observed in order of decreasing temperature. The relaxation time for the αn relaxation increases with increasing molecular weight and is assigned to the normal mode relaxation due to the component of dipole vector aligned in the direction parallel to the chain contour. The αs relaxation is observed about 30 K above the glass transition temperature Tg (= 310 K) and is assigned to the local segmental mode due to the transverse component of the monomeric dipoles. The β relaxation is seen in the glassy state and is assigned to the secondary relaxation. From the relaxation strengths for the αn, αs, and β relaxations, the effective dipole moments for those relaxation processes are determined and compared with the parallel and transverse components of the dipole moment calculated theoretically with the semiempirical molecular orbital methods. The d...

Dielectric relaxation of the segmental mode in concentrated solutions of poly(vinyl acetate) (PVAc) in toluene (Tol) and in 1-methylnaphthalene (MN) and those of poly(vinyl octanoate) (PVOc) in Tol were studied. It was found that the distributions of relaxation times in concentrated solutions were much broader than those in dilute solution and in the undiluted bulk polymer. The broad spectra were ascribed to local heterogeneities. The half width Λ increased with decreasing temperature and this behavior was explained by assuming that Λ is proportional to the amplitude of the local concentration fluctuation Δφ times the slope of the φ dependence curve of the average relaxation time τ . This assumption leads to a linear relationship between Λ and Δφ /( T − T 0 ) 2 where T 0 is the Vogel critical temperature. Using this relation, we attempted to estimate Δφ .

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 40 wt% 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.

We investigated ultrasonic attenuation, dynamic Young's modulus, Izod impact strength, and dielectric relaxation of acrylonitrile–butadiene–styrene composite polymers (ABS) in which styrene-co-butadiene rubber particles are dispersed in styrene-co-acrylonitrile random copolymer. High ultrasonic attenuation was observed around 240 K and the intensity of attenuation increased with increasing rubber content. Temperature dependence curves of dielectric loss in the frequency range from 12 Hz to 200 kHz and temperature range from 80 to 420 K exhibited four relaxation processes designated as the α, β′, β, and γ. From the relaxation map produced for the mechanical and dielectric relaxations, the ultrasonic absorption was attributed to the β and β′ processes. It was deduced that inter-grain thermoelastic process, also contribute to the ultrasonic attenuation. Correlation was found between the ultrasonic absorption and the Izod impact strength indicating that the high impact strength of ABS is partly due to the effective absorption of impact energy through those relaxation processes.

Dielectric measurements were carried out for linear and star-shaped poly(propylene glycol)s (PPGs) of different molecular weights (M). A small loss peak due to the normal mode relaxation was observed on the low-frequency side of the main loss peak. Two peaks were resolved and the normal mode relaxation time τn, the distribution of relaxation times and relaxation strength were examined. The effect of OH groups attached at the chain ends on the normal mode relaxation was also investigated by using PPG samples whose end groups were substituted by acetyl groups. The results indicate that τn is proportional to M2 in accordance with the Rouse theory. The mode distribution of star-shaped PPGs is slightly broader than that of linear PPGs. The effect of hydrogen bonding between the OH groups on the normal mode relaxation time is negligibly small.

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.

The effect of local heterogeneity on the distribution of dielectric relaxation times was studied for concentrated solutions of poly(vinyl acetate) (PVAc) in 1-methylnaphthalene (MN) and those of poly(vinyl octanoate) (PVOc) in toluene (Tol). The half-widths A of the dielectric loss curves for the primary processes of those systems are compared with those of the PVAc/Tol system reported previously. The data indicate that A decreases in order of PVAc/Tol, PVAc/MN, and PVOc/Tol systems if compared at the same temperature T/Tg where Tg denotes the glass transition temperature of solutions. The half-width of each solution increases with decreasing temperature. The loss curve is calculated by assuming a Gaussian distribution of the local concentration Φ which results in the distribution of relaxation times g(τ). The calculated loss curves agree fairly well with the observed ones. The broadening behavior is also explained by assuming that A is proportional to the amplitude of the local concentration fluctuation ΔΦ times the slope of the Φ dependence curve of the average relaxation time r. This assumption leads to a linear relationship between A and ΔΦ/(T - T 0 ) 2 where To is the Vogel critical temperature. Using this relation, we have attempted to estimate ΔΦ. Small-angle X-ray scattering was also measured on PVAc/ MN solutions and found that the scattering intensity was lower than that for PVAc/Tol. This is consistent with the fact that A of PVAc/MN solutions is narrower than PVAc/Tol solutions.

Dielectric measurements were carried out on blends composed of poly(n-butyl acrylate) (PBA) and poly(propylene glycol) (PPG) exhibiting phase behavior of the UCST type. Both linear PPG and three-ar...

We report the cloud point, glass transition temperature Tg, and dielectric relaxation for blends composed of poly(n-butyl acrylate)s (PBA) and a linear poly(propylene glycol) (PPGD) and for blends of PBA and a star-shaped PPG having three arms (PPGT). The phase diagram is of the upper critical solution type (UCST), and the critical temperature varies from 340 to 220 K depending on the molecular weight of the PBA. The interaction parameter χ for PBA/PPGD is higher than that for PBA/PPGT. For blends of high molecular weight PBA and PPGD, a sharp glass transition and a subsequent broad glass transition were observed by differential scanning calorimetry, but for mixed blends a relatively sharp single Tg was observed. The temperature dependence of the dielectric loss factor e‘ ‘ of phase-separated blends exhibited two loss maxima. The low-temperature peak can be assigned to the segmental mode relaxation (α-process) of PPG and the high-temperature peak to the normal mode of PPG and the segmental mode of PBA. Mi...

Viscoelastic and rheo–dielectric properties were investigated for suspensions composed of barium titanate (BaTiO3) particles having an average size of 0.3 μm and polydimethylsiloxane (PDMS). Steady shear viscosity decreased with increasing shear rate. Stepwise increase of shear rate resulted in a thixotropic decrease of the viscosity due to reorganization of aggregates of the BaTiO3 particles in the shear field. The transient change occurred through the fast and slow processes with the time constants of 5–30 and ca 100 s, respectively. Yield stress and plasticity were also observed for suspensions of high BaTiO3 content. Since BaTiO3 particles possess a strong dipole moment due to spontaneous polarization, the suspensions exhibited dielectric dispersion due to reorientation of the particles. The dielectric constant decreased with increasing viscosity of PDMS due to the increase of the dielectric relaxation time in the viscous medium. In order to investigate the aggregation of the particles in a shear field, we also carried out rheo–dielectric measurements in shear fields. The dielectric constant in a shear field decreased with increasing shear rate. After sudden stop of shear flow, a recovery of the dielectric constant was observed and was resolved into the fast and slow processes. The characteristic time for the fast process was close to the relaxation time for the thixotropy. Those results were explained by assuming chain-like aggregates of BaTiO3 particles formed by the dipole–dipole interactions.

Piezoelectric elastomers were prepared from suspensions of bariumtitanate (BaTiO 3 ) particles in a telechelic polydimethylsiloxane (t-PDMS) by crosslinking the t-PDMS under an electric field. Crosslinking reaction was monitored by measurement of complex dielectric constant e' - ie. Dielectric constant e' increased with increasing BaTiO 3 content, and agreed approximately with the theoretical e' calculated with the Maxwell-Wagner theory. Piezoelectric constant d 33 of the poled elastomers was measured by application of compressions in the direction of the poling field. It was found that d 33 was of the order of 10 -11 C/N and increased steeply with increasing content of BaTiO 3 but became almost independent of composition in the range of BaTiO 3 content from 3 to 14 vol %. To examine the effect of electric field on the aggregation structure of the particles, we observed light scattering of the suspension under an electric field, and found that the scattering pattern became anisotropic. This indicated that the particles are connected like a pearl necklace and are stretched in the direction of the poling field. The dependence of d 33 on the volume fraction of BaTiO 3 was explained by a model proposed by Banno.

A dynamic Monte Carlo algorithm is employed to investigate the dynamics of flexible linear and star chains on a cubic lattice at different concentrations. Some results for similar systems are also obtained with an off-lattice algorithm. Diffusion coefficient, relaxation times and mean size data are combined into friction-independent ratios in good agreement with the theoretical predictions from the Rouse theory. The relaxation times and amplitudes corresponding to the Rouse normal modes are analyzed in terms of their variation with the mode order. The end-to-end vector correlation times obtained from the simulations for linear chains are compared with the theoretical expression obtained from the Rouse theory. Deviations from this theory are observed for the contribution of the different modes in the non-dilute systems. Finally, the time correlation function corresponding to a subchain's end-to-end vector is investigated. The results also show deviations from the Rouse theory, which are in qualitative agreement with the features observed in data from dielectric relaxation experiments of block copolymers.

We report on the dielectric normal mode relaxation of the isoprene block chains in dilute and semidilute solutions of butadiene–isoprene (BI) diblock copolymers and butadiene–isoprene–butadiene (BIB) triblock copolymers. The dielectric loss e″ curves in dilute solutions with a concentration close to the overlapping concentration C* agreed approximately with those predicted by the bead–spring model. Above a concentration about three times higher than C*, the e″ curves broadened with increasing concentration indicating the strong concentration dependence of the distribution of the normal modes. Two maxima of the e″ curves were observed for BIB solutions. In semidilute solutions of BIB, the e″ peak located in the high frequency side shifted little with concentration but the e″ peak in the low frequency side shifted towards low frequency with increasing concentration. This suggests that the lower order normal modes are affected by entanglement effects but the higher order modes are not, for semidilute solutions. We have attempted to explain the distribution of the normal modes in terms of the blob model.

Dielectric measurements were carried out on undiluted cis-polyisoprene (PI) over a wide frequency range from 10-4 to 105 Hz around the glass transition temperature Tg (=200 K). The data indicate that the dielectric loss curves including both the normal and segmental mode processes are superposable in the range above 230 K (Tg + 30 K). Below 230 K, the time−temperature superposition is not applicable to the whole loss curve. The ratio of the relaxation times of the normal and segmental modes is constant above 230 K but decreases below 230 K with decreasing temperature.

Dielectric spectroscopy was applied to study dynamics of cis-polyisoprenes (PI), used as type-A probe, in blends with polybutadiene (PB) and in block copolymers with polystyrene (PS) of SI- and SIS-type. For dilute high-molecular weight (M) PI/low- M PB blends we identified Rouse mode with M 2 -dependent relaxation time T, while for low- M PI/high- M PB blends, we identified pure reptation mode with M 3 -dependent τ. In between τ ∞ M α with the exponent α varying from 2 to 3 as M B was increased, as suggested by Graessley with constraint release via tube renewal mechanism. For the blends with the MW ratio M I /M B ≃ 2.5, we found bulk polymer behaviour with τ ∞ M 3.5 , in which competition between pure reptation and tube renewal appear to be essential and the contribution of contour length fluctuation may be ruled out. For SI-diblock copolymers between Tg(I) Tg(S), exhibiting broadening due presumably to their micao-phase-separated structure. The relaxation mechanisms for such end-capped I-chins in SIS-triblock copolymers could be junction hopping in those with isolated S-domains but chain rotating in those with S continuous morphologies.

Miscibility of polymer blends around the critical solution temperatures was studied by using a dielectric method for the system composed of low molecular weight cis-polyisoprene (cis-PIp) and polystyrene (PSt) and the system of cis-PIp and vinylpolyisoprene (vinyl-PIp). All these polymers exhibit the dielectric relaxation due to the segmental mode and cis-PIp also exhibits the normal mode relaxation. In the cis-PIp/PSt blend, the normal mode relaxation conformed to the blending law, indicating that the blend is homogeneous over a length scale of the end-to-end distance. On the other hand the cis-PIp/ vinyl-PIp system exhibited a complex loss curve mainly due to the segmental mode of vinyl-PIp. The shape of the loss curve varied with temperature, indicating that the blend is weakly segregated and that the degree of inhomogeneity of the length scale of the monomeric unit varies with temperature.

Polyisoprene (PI) possesses type-A dipole moment aligned in the direction parallel to the chain contour and exhibits the dielectric normal mode relaxation due to the fluctuation of the end-to-end vector. Using this property of PI, we have studied the dynamics of the PI block chains of styrene-isoprene diblock copolymers (SI) and styrene-isoprene-styrene triblock copolymers (SIS). The results indicate that the distribution of relaxation times in SI having the lamella morphology is broadest and the distribution becomes narrow in order of cylinder and sphere morphologies. In SIS the dielectric normal modes are observed in the temperature range above the glass transition temperature of the styrene domain indicating that the styrene block chains can jump from one domain to the other.

The order−disorder transition (ODT) of semidilute solutions of polystyrene-block-polyisoprene in toluene was studied by small-angle X-ray scattering (SAXS) and dielectric relaxation. Both methods c...

A Stockmayer's type-A chain such as cis-polyisoprene (PI) having dipole components parallel to the chain contour exhibits slow dielectric response, reflecting fluctuation of its end-to-end vector (dielectric normal modes). This article reviews our own work on dielectric spectroscopy for studying dynamics and conformational properties of probe PI chains in binary blends with PI or polybutadiene (PB) that does not exhibit normal modes. Through such studies we were able to see the crossover of the probe-chain dynamics from Rouse behaviour in low-molecular-weight (lmw) matrices to pure reptation behaviour in high-molecular-weight (hmw) matrices. We were also able to confirm experimentally Flory's earlier prediction on excluded volumes in dilute blends of hmw probe chains in lmw matrices, for which a proof has never been given before.

Dielectric normal mode relaxation was studied on blends containing a small amount (∼5 wt %) of probe cis-polyisoprenes (PI) in a series of polybutadienes (PB) of different molecular weights M B . Since the PI chain has Stockmayer's type-A dipoles parallel to the chain contour, while PB chains do not, we can study global motion dynamics of the probe chain under various entanglement conditions between PI and PB chains. The dielectric normal-mode relaxation time τ of PI with molecular weight M I followed a power law relation τM I α with a varying from 2 to 3 depending on M B : For M B 20 000, α=3.0, conforming to the pure reptation model, and in the range 3000 1) was larger than 3 and became 3.7 (observed for monodisperse PI melts) at M I /M B ≃ 2-3. These findings were consistently interpreted with Graessley's constraint release model. The shape of the dielectric loss curves (reflecting the distribution of relaxation times) of the blends agreed rather well with the Rouse model when M I /M B > 10 and M B M eB ) especially in the high-frequency tail, as usually observed in monodisperse PI melts

We studied the dielectric normal mode relaxation in dilute and semidilute solutions of poly(e-caprolactone) (PCL) and poly(δ-valerolactone) (PU) in benzene using narrow distribution samples prepared with an initiator of a lanthanoid complex. The effect of long nonpolar groups separating the polar ester groups on the dielectric behavior was investigated by comparing the present results with those for cis-polyisoprene (PI) solutions reported previously. In dilute solutions, the longest relaxation time r for both PCL and PU increased in proportion to M 1.63±0.03 . The double-logarithmic plots of r us [η]η s M/RT for the dilute solutions as well as those of PI fell on the same universal straight line irrespective of the solvent quality

Dielectric normal mode relaxation was studied for dilute and semidilute hexane solutions of butadiene (B)-isoprene (I) block copolymers in which the polyisoprene block has the component of dipole moment aligned parallel to the chain contour (Type-A dipole moment) while the polybutadiene block does not. Thus, the fluctuation of the end-to-end vector of a portion of a chain labeled by type-A dipoles was observed. The results indicate that BI diblock copolymers exhibit a single loss peak while BIB triblock copolymers exhibit double peaks. This behavior can be qualitatively explained by the Rouse-Zimm theory. In dilute solutions, the loss maximum frequency and the shape of the loss curve agree well with the Zimm theory. In semidilute solutions, the loss curve broadens more than the theoretical loss curve calculated by either the Rouse theory or the Doi-Edwards theory. The broadening of the loss curve can be explained by the coupling theory proposed by Ngai and his co-workers. The mean square end-to-end distance, 〈r2〉, of the PI block was estimated from the relaxation strength, Δϵ. The expansion factor, α, for 〈r2〉 agreed approximately with that of homo PI solution in heptane.

Stockmayer's type-A chain such as cis-polyisoprene (PI) having dipole moments aligned parallel to the chain contour exhibits slow dielectric response, reflecting fluctuation of the end-to-end vector of the chain (dielectric normal modes). This article intends to review our own work on dielectric spectroscopy using PI as a probe for studying dynamics of large scale motion of the probe chain in binary blends with polybutadiene (PB) and in block copolymers with PB or with polystyrene. Through such studies we were able to see the features of polymer chain dynamics in various environments: Rouse-Zimm-like dynamics in overlapping-but-unentangled regimes, reptation with and without accompanying constraint release, behaviour of a subchain incorporated into block copolymers with miscible segments, and dynamics of polymer brushes in strongly segregating block copolymers in bulk and in solutions.

Dynamics of a trace amount of cis-polyisoprene (PI) dissolved in semidilute polybutadiene (PB)/n-heptane (Hep) solutions as a probe was examined through dielectric normal mode relaxation studies and compared with the results of semidilute PI/Hep solutions. In PI/Hep solutions, the dielectric normal mode relaxation time of PI conforms well to the Muthukumar-Freed theory. It was found that τ of PI internary PI/PB/heptane solutions was expressed by the scaling form τ/τ 0 ≃ G(C PB [η] PI , C PB [η] PB . In the ternary solutions, the dynamics of the guest PI chains in PB solution changes from Zimm-like behavior at infinite dilution to Rouse-like and reptation mechanisms with increasing C PB [η] PI

Dielectric normal mode relaxation of a trace amount of cis-polyisoprene (PI) mixed in semidilute heptane (Hep) solutions of polybutadiene (PB) was studied and compared with semidilute PI/Hep solutions. The concentration dependence of the mean square end-to-end distance of PI was compared to those in PI/Hep and PI/PB/Hep solutions. In PI/Hep, the (r 2 ) decreased with PI concentration C 1 in proportion to C -0.152 . In PI/PB/Hep the C 1 was fixed to be 0.2 or 0.4 wt% and the PB concentration C B was changed from dilute to semidilute regimes.

Electric conductivity and sol-gel transition behavior were studied for gels of a polydiacetylene poly[4,6-decadiyn-1,10-diol-bis(n-butoxy-carbonylmethyl urethane)] abbreviated to P(3BCMU). Two solvents with different dielectric constant were used, i.e., o-dichlorobenzene (o-DCB) and a mixed solvent of p-dichlorobenzene (p-DCB) and toluene (TOL). Temperature dependence of the shear moduli G′ was measured to determine the gel-to-sol transition temperatures Tt at which the moduli decreased steeply. The Tt was 378 K in o-DCB and 387 K in p-DCB/TOL (62/38). Both direct current (DC) conductivity σdc and alternating current (AC) conductivity σac at 1 kHz exhibited a maximum around 368 and 362 K in o-DCB and p-DCB/TOL, respectively. Dopant effects of an electron acceptor iodine and a donor tetrathiafulvalene TTF on σdc and σac were also studied. σac was enhanced approximately by 100 times with iodine but only by 5 times with TTF. The pronounced dopant effect indicates that the conduction in the gel state is partly due to electronic conduction through the P(3BCMU) chains. We also observed an appreciable strength of ionic conductivity in the sol and gel phases. The ionic conductivity in the gel phase was estimated from σac of the solvent containing the ions extracted from the gel phase. Then observed σac and σdc were separated into the contributions of ionic and electronic conductions. Electronic conductivity increased with increasing dielectric constant of the solvent. Transition temperature Tt where the color changed from blue to yellow was also determined by measuring the transmittance at 630 nm wave length. The temperature dependence of the transmittance indicated a hysteresis.

The dynamics of cis-polyisoprene (I) blocks tethered on glassy polystyrene (PS) domains in microphase separated styrene-isoprene (SI) diblock copolymers in bulk, in blends with PS-polybutadiene (SB) diblock copolymer, and also in solution of n-tetradecane (C14) that is a nonsolvent to S blocks, is studied

For solutions of diblock polystyrene-cis-polyisoprene (poly-SI) in toluene, strong influences of the microphase separation on the dielectric normalf-mode relaxation of the I-blocks involved were found. In microphase-separated poly-SI solutions at high concentrations and/or low temperature, the I-blocks exhibit broad double-peaked e curves. In such solutions, the S-phase diluted with toluene is liquid and the S-I junction points are movable. The high-f mode of the polySI solution is attributable to the fluctuation of such junctions in the S-I interphase, and the low-f mode to the fluctuation of the free I-ends

The dielectric normal-mode relaxation was studied on dilute blends containing a small amount of cis -polyisoprenes (PI) as a probe in a variety of matrices such as high molecular weight (MW) cis -PI and alkyllithium-polymerized polybutadiene (an-PB), and networks of natural rubber (NR), cis -PB ( cis -BR) and an -PB (an- BR). In the dilute blends of non-cross-linked high-MW PI or PB and low-MW probes with M ≧ M e 0 (⋍ 5000 , the MW between entanglemen for bulk PI), the relaxation time τ n , of the probe was proportional to M 3 , obeying the original tube model. However, the M dependence of τ n of PI probes trapped in NR or BR networks was puzzling: for those in NR and in high cis -BR, τ n ∝ M 3.6 , which is similar to bulk narrow-distribution PI; while for those in an-BR, τ n ∝ M 3 , which is similar to that of the dilute blends of low- M probes in non-cross-linked high-MW matrices.