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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...

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.

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.

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 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...

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...

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...

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.

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.

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.

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...

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

Dissociation equilibria of lithiumthiocyanate (LiSCN) in N,N-dimethylformamide (DMF) solutions of poly (propylene oxide) (PPO) were investigated by using infrared spectroscopy. The stretching bands due to the thiocyanate ions SCN−1 and the LiSCN ion pair were found at 2058 and 2072 cm−1, respectively. At high LiSCN concentration C of ca. 20 wt %, another weak band due to the dimer (LiSCN)2 was observed. From the ratio of the areas of the absorption bands, the dissociation constant K1 for the equilibrium LiSCN ↔ Li+ + SCN−1 and that K2 for (LiSCN)2 ↔ 2LiSCN have been determined. With increasing DMF content, K1 increases from 1 × 10−4 for bulk PPO to 4.8 × 10−1 for pure DMF at 299 K. Log K1 is not linear against inverse of the dielectric constant ϵ of the medium and decreases with increasing temperature. The enthalpy (ΔH) and entropy (ΔS) changes for the dissociation of LiSCN are both negative. ©1995 John Wiley & Sons, Inc.

Ionic conductivity σ, shear viscosity η, and glass transition temperature Tg were measured on systems composed of lithiumthiocyanate LiSCN, N,N-dimethylformamide (DMF), and poly (propylene oxide) (PPO) over wide ranges of LiSCN concentration C and DMF content Φ. Using the dissociation constant of LiSCN reported in Part I, we have determined the concentration n of Li+ and SCN− ions and then the mobility μ from σ. Data indicate that in the binary system of LiSCN/PPO, the σ versus C curve exhibits a maximum ca. C = 0.3 mol/L. In low C range, μ is independent of C but decreases with C in the range of C > 0.3 mol/L. Similar n dependence of μ is seen in the ternary systems containing DMF. The ratio of μ0/μ (C) is lower than the ratio of viscosity η(C)/η0 where μ0 and η0 indicate the values at infinite dilution of LiSCN. Thus the friction coefficient ςion for the translational diffusion of the ions is not proportional to the macroscopic viscosity. Relationship between μ and the monomeric friction ςp for the segmental motion of the PPO chains is also discussed based on the data of Tg and the Williams-Landel-Ferry equation. ©1995 John Wiley & Sons, Inc.

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

Dynamic light scattering in the depolarized geometry has been used to investigate the behavior of solutions of an asymmetric diblock copolymer in a nonselective good solvent near the orderd-order transition (ODT), as a function of concentration, temperature, and scattering vector, q. A new q 2 -dependent relaxation with q-dependent amplitude and depolarized intensity appear in the correlation function when the solution crosses from the disordered into tge ordered state, which is accompanied by a significant increase in the depolarized intensity

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.

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 process of bifurcated linear cis-polyisoprenes (PI), which are composed of two linear PI arms connected in a head-to-head fashion and have dipoles along the chain contour inverted once at the center, was compared with that of regular linear PIs without dipole inversion, and also with that of six-arm star PIs with dipoles diverging from the center to the arm ends

Determination de la distance bout a bout quadratique moyenne d'un cis-polyisoprene monodisperse a masse moleculaire elevee melange a 0,5-5% avec un cis-PI a masse moleculaire faible. Dans les melanges dilues, le cis-PI a une conformation allongee

We present a comparison of the Rouse theory with Monte Carlo results for the end-to-end vector time correlation function obtained in previous work and also with previously obtained experimental data for dielectric relaxation, in both the dilute and nondilute regimes

Relaxation dielectrique due a la fluctuation de la distance bout a bout de solutions dans le benzene et le dioxanne

Etude de la relaxation en mode normal du PI cis dans une solution de PB cis dans le benzene: diminution du temps de relaxation avec la fraction massique du PI hote, due aux variations du coefficient de frottement monomerique et de l'effet d'enchevetrement; variation du temps de relaxation avec le degre de confinement topologique du PI du aux chaines voisines. Distance bout a bout quadratique moyenne du PI inferieure a la dimension non perturbee

Mesure de la distance bout a bout dans l'hexadecane et l'eicosane et comparaison avec les valeurs obtenues dans le benzene et la dioxanne. Evaluation du parametre d'interaction κ selon la theorie de Flory a partir du facteur d'expansion des molecules de polymere. Courbe logarithmique de la distance /M en fonction de C montrant 4 regimes de variation: dilue, semi-dilue, semi-concentre et ion

Relaxation dielectrique due a la fluctuation de la distance bout a bout appelee «mode normal» et une autre due au mode segmental. Comparaison des temps de relaxation pour les deux processus

Relaxation dielectrique due a la fluctuation de la distance bout a bout des chaines du polymere dans le chlorobenzene. Influence de la masse moleculaire et de la ramification de chaine

Preparation du polybutadiene reticule par reticulation radiochimique en solution dans le toluene et etude du gonflement du PB dans des solutions de polyisoprene cis dans le benzene. Augmentation du taux de gonflement q et du taux d'absorption A par diminution de la concentration de reticulation Cx. Analyse des resultats en s'appuyant sur la theorie de Flory-Rehner

Proprietes dielectriques de solutions dans le toluene pour montrer l'influence de la microstructure sur le comportement dielectrique

Processus de «mode normal» de la relaxation dielectrique due a la fluctuation ou la polarisation bout a bout, pour un cis-polyisoprene absorbe sur un caoutchouc naturel reticule et sur un caoutchouc isoprene synthetique

Dynamic light scattering in the polarized geometry has been used to investigate the dynamics of composition fluctuations in solutions of two poly(styrene-block-1,4-isoprene) diblock copolymers in a nonselective, good solvent both far from and near to the ordering transition. Four different relaxation mechanisms were identified. One relaxation relates to the cooperative diffusion of copolymer chains, and it behaves similarly to that in semidilute homopolymer solutions. As concentration increases, two additional relaxations gain in amplitude: the wavevector-independent internal or breathing mode, predicted by theory, with amplitude increasing with scattering angle, and the recently established for copolymer melts diffusive relaxation; the relation times of both processes increase with copolymer concentration