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We studied the relationship between segmental dynamics of matrix polymers and tracer diffusion of low mass compounds by the use of forced Rayleigh scattering and dielectric spectroscopy. Specifically poly(methyl acrylate), poly(ethyl acrylate) and poly( n -butyl acrylate) were used as the polymer matrices and six azobenzene derivatives with various substituents as the diffusant. The temperature dependence of the tracer diffusion coefficient D was measured on methylyellow (MY)/polyacrylate blends at the MY concentration of 1 wt%. The results indicate that the temperature dependence of D is weaker than the dielectric loss maximum frequencies f m for the α processes of the matrices. The effect of volume of the dye molecules on D was also investigated at 305 K. Comparison of the tracer diffusion coefficients among various dye/polymer systems indicates that log D in the same matrix decreases linearly with the molar volume of the dyes.

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.

We investigated the interfacial tension γ between poly(ethylene oxide) (PEO) and polystyrene (PS) focusing our attention on the dependence of γ on the molecular weight ( M ) of PEO and the surfactant effect of poly(ethylene oxide- b -styrene) diblock copolymer [P(EO- b -S)]. Measurements of γ were carried out by observing electric deformation of droplets of PEO suspended in bulk PS or in a concentrated solution of PS in dioctylphthalate (DOP). The results indicate that γ between PEO and PS is almost independent of M of PEO in the high molecular weight region, but exhibits a minimum around M = 500. Addition of 1 wt% of P(EO- b -S) to the PEO/PS system causes a decrease of γ due to the surfactant effect of the copolymer, but γ is almost independent of further addition of the copolymer. The decrement of the interfacial tension Δ γ increases with increasing molecular weight of P(EO- b -S).

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(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.

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 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.

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...

Relationship between segmental relaxation and normal-mode relaxation has been studied for molten poly(butylene oxide)s having various molecular weights by broadband dielectric spectroscopy over a wide temperature (T) range. We found that T dependence of the segmental relaxation time, τs, was weaker than the normal mode time, τn, at high T(>250 K ∼ Tg + 50 K), and the τn/τs ratio systematically decreased with increasing temperature. This high temperature complexity, whose mechanism has not been discussed in detail so far, was quantitatively explained by assuming the two step processes: local conformation change of polymers (elementary process) occurs first, and then the motion of a segment unit (second process) occurs. It was also found that the elementary process was strongly correlated with the experimentally observed β-relaxation.

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.

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...

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.

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 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 composition, f, and concentration, ϕ, dependence of the self-diffusion coefficients of diblock copolymers in solutions in a common good solvent have been investigated by pulsed-field-gradient nuclear magnetic resonance and photon correlation spectroscopy. The difference in the entanglement characteristics of the parent homopolymers was found to be very important in determining the diffusion coefficients. The investigation on toluene solutions for a series of poly(styrene-b-isoprene) diblocks, possessing almost similar molecular weights and compositions ranging from 0.18 to 0.74, showed that the dependence of the diffusivity on diblock composition f conforms with the progressive transition from the Rouse to the entanglement regime at different concentrations due to the different critical molecular weights for entanglement of the parent homopolymers. The same idea can account for the diblock composition dependence of the self-diffusivity for poly(styrene-b-butadiene) diblocks. Moreover, the self-diffusivities for three poly(styrene-b-methyl methacrylate) diblocks in toluene are insensitive to copolymer composition (0.35 to 0.69) in accord with the very similar entanglement characteristics of the two blocks.

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...

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

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.

Alternating current conductivity σac, shear moduli G′, and ultraviolet-spectra (UV) were studied for gels consisting of two polydiacetylenes i.e., poly[4,6-decadiyn-1,10-diol-bis(n-butoxy-carbonylmethyl urethane)] abbreviated as P(3BCMU) and poly[5,7-dodecadiyn-1,12-diol-bis(n-butoxy carbonyl methylurethane)] abbreviated as P(4BCMU). As a common solvent of these polydiacetylenes, a mixed solvent p-dichlorobenzene (p-DCB)/toluene (TOL) (62/38) was used. Shear moduli G′ of blend gels decreased stepwise around 340 and 385 K which coincided with the gel-to-sol transition temperatures of pure P(4BCMU) and P(3BCMU) gels, respectively. At 385 K the blend gels transformed completely into sol. Observed G′ of blend gels conformed approximately to the additivity law with respect to the weight fraction of P(3BCMU) and P(4BCMU). This indicates that in the range of T

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.

We report the effect of phenol on the phase behaviour and physical properties of polydiacetylene gels. Specifically, they are o -dichlorobenzene ( o -DCB) solution of poly[4,6-decadiyne-1,10-diol-bis(n-butoxycarbonylmethylurethane)], abbreviated as P(3BCMU), and toluene (Tol) solution of poly[5,7-dodecadiyne-1,12-diol-bis(n-butoxycarbonylmethylurethane)], abbreviated as P(4BCMU). The polymer concentration was 0.1 to 2 wt%, and the molar ratio z of phenol to the monomer unit of the polydiacetylenes was regulated within 20. The gel-to-sol transition temperatures T t were determined by measurements of shear modulus for the P (3 BCMU ) o- DCB system and by a falling ball method for the P(4BCMU)/Tol systems. T t decreased with increasing z and the systems with polymer concentration of 1 wt% turned into a sol at room temperature in the range of z ≳ 10. The temperature dependence of alternating-current (a.c.) conductivity σ ac at 1 kHz exhibited a maximum at a temperature ca. 20 K below the transition temperature. The value of σ ac decreased steeply at the electrical transition temperature T σ , which also decreased with increasing z . Ultra-violet and visible-light spectra for the P (3 BCMU ) o- DCB and P(4BCMU)/Tol systems shifted to the short-wavelength side with increasing z . The infra-red spectra indicate that the intramolecular hydrogen bonds between the NH and CO groups of the side groups are cleaved by phenol. These results indicate that the conjugated rod-like conformation is made unstable by phenol. To clarify the mechanism of crosslinks of the gel network, the crystallinity of concentrated P(3BCMU) gels was determined by wide-angle X-ray diffraction. No crystallinity was observed in the gels of C less than 30 wt%.

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

Deformation of droplets under an electric field was studied on aqueous poly(acrylamide) solutions suspended in poly(dimethylsiloxane).

Deformation of viscoelastic droplets in an alternating current electric field of 60 Hz was studied on aqueous solutions of cetyltrimethylammonium bromide-sodium salicylate complex suspended in poly(dimethylsiloxane).

We investigated the dielectric normal mode relaxation of the polyisoprene (PI) block chain of styrene-isoprene diblock copolymer (SI) and styrene-isoprene-styrene triblock copolymers (SIS) in semi dilute and concentrated solutions. Solvent was a common good solvent toluene (TOL). The order-disorder transition (ODT) was reflected on the dielectric loss curves ɛ″: In the ordered state, SI solutions exhibited a bimodal ɛ″ curve but a single peak in the disordered state. In this paper we investigated the molecular mechanism of the bimodal relaxation spectra in the ordered phase using solutions of non-symmetrical SI, triblock copolymers SIS, and styrene-butadiene-isoprene triblock copolymers (SIB and SBI). In order to detect the ODT we also carried out the measurements of heat capacity on an SI/TOL system. The bimodal relaxation spectra in the ordered state was ascribed to the difference in mobility of the chain ends of the PI block. From the dielectric data for solutions of SIS, SIB, and SBI in TOL, we concluded that the high and low frequency peaks of the ɛ″ curves can be ascribed to the motion of the end at the interface and that of the free end, respectively.

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

The dielectric normal mode process was investigated on semi-dilute and concentrated solutions of poly(2,6-dichloro-1,4-phenylene oxide)(PDCPO-M) in a good solvent, chlorobenzene, at 300 K. Four linear, short chain samples with molecular weight M less than 20×103, two nearly linear samples of intermediate M, and a high M, randomly branched sample (PDCPO-380) of M=380×103 were used. The dielectric relaxation time τ for 40 wt% solutions of the linear samples was approximately proportional to M2, indicating Rouse behavior of non-entangled chains. The loss curves of the PDCPO-17 solutions were symmetrical in shape, and the half width A increased slightly with increasing concentration C due presumably to the increase in the local friction constant ζ. On the other hand, for the branched, high M PDCPO-380 sample, its loss curve not only became broader with increasing C, but split into two peaks at about C=30 wt%. This is presumably because the relaxation time of longer branches of the sample were retarded more strongly by entanglement. From the relaxation strength, the mean square end-to-end distance ‹r2› was determined as a function of C for PDCPO-17 solutions. The slope of the log‹r2› vs. logC plot was approximately −0.08 in the range of 0.2

The dielectric, mechanical and thermal properties were investigated for poly(2,6-dichloro-1,4-phenylene oxide) (PDCPO), poly(2-chloro-6-methyl-1,4-phenylene oxide) (PCMPO) and poly(2,6-dimethyl-1,4-phenylene oxide) (PDMPO). PDCPO exhibited two dielectric secondary relaxations designated as β and γ processes around 160 and 100K, respectively. The γ process was assigned to the motion of a trace of chloroform included in the PDCPO film. A blend film PDMPO/PCMPO ( 9 1 mixing ratio) exhibited dielectric relaxation around 330K and the process was assigned to the rotation of phenyl group with respect to oxygen-phenyl-oxygen axis. No dielectric relaxation was observed for the PDMPO film dried carefully, while the PDMPO film kept under an atmosphere of water vapour exhibited dielectric relaxation due to the motion of the water molecules at about 180K. Tensile stress at break measured on PDCPO prepared by Stamatoff's method was 38 MPa and was much higher than that for PDCPO prepared by the method reported by Blanchard et al. Temperature dependence of the dynamic Young's modulus for PDCPO measured at 110 Hz exhibited no appreciable loss peak in the range below 480K. Glass transition temperatures for PDCPO, PCMPO and PDMPO were determined to be 490, 445 and 500K, respectively, by differential scanning calorimetry.

A study was carried out on the effects of thermal aging on specific volume V and specific enthalpy H of polystyrene below the glass transition temperature. The dependence of V and H on annealing time was similar. No significant effect of the distribution of molecular weight on the relaxation behavior was found. The behavior of V and H reaching a maximum after a double-step temperature-jump was also investigated. The time for the maximum V and H varied in proportion to the period of pre-annealing. The time for the maximum volume was slightly longer than that for the maximum enthalpy. These facts indicate that the dependence of V and H on the order parameters specifying the glassy state are similar but not exactly the same. From the enthalpy and volume relaxation curves, the enthalpy required for creating free volumes in polystyrene was calculated to be 2.0 kJ cm−3. The behavior of the volume relaxation was discussed by assuming a wide distribution of relaxation time.