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Time-resolved light-scattering measurements have been performed on poly(vinyl alcohol) (PVA) in mixed solvents of dimethyl sulfoxide (DMSO) and water with various mixing ratios after quenching from...

The effect of isotacticity on the mesomorphic phase-forming properties of isotactic polypropylene (iPP) is reported. Only iPP having high isotacticity (iPP-HT) can form the mesomorphic phase by a rapid quench, but iPP having low isotacticity (iPP-LT) cannot form the mesomorphic phase though it crystallizes by the same quenching rate. These results suggest that the mesomorphic phase of iPP is closely related to the stereoregularity of the polymer chain. The mesomorphic phase in the iPP-HT shows longer regular 3/1 helices than in the crystalline iPP-LT. The structure and formation mechanism of the mesomorphic iPP are considered analogous to those of liquid crystals since the average length of the long regular 3/1 helices in the mesomorphic iPP acting as rodlike segments is sufficiently large to fulfill a criterion for the formation of liquid crystalline phase. From this criterion, the minimum requirement of isotacticity to form the mesomorphic phase is also estimated.

The local dynamics of 10 substituted polyacetylenes in the glassy state have been investigated using a quasielastic neutron scattering technique in a time range of picoseconds to several tens of picoseconds to see a relationship between the local mobility and the gas permeability of these polymers. Even in the glassy state, these polymers show quasielastic scattering components, suggesting that certain stochastic motions occur in the glassy state. The dynamic scattering laws S(Q,ω) of the quasielastic components were well fitted to the sum of two Lorentzians, i.e., the narrow (slow) and broad (fast) components. It was found that both the relaxation rate Γn and the fraction An of the narrow (slow) component show positive correlations with oxygen permeability coefficient (PO2), suggesting that the local mobility of the matrix polymers plays an important role in gas permeability. We then defined local flux F, which is the product of Γn and An, as a measure of the local mobility to find that F is proportional...

The intermolecular correlation due to electrostatic repulsion in flexible polyelectrolyte solutions as a function of ionic strength has been studied using small-angle neutron and X-ray scattering (SAXS and SANS) techniques. The ionic strength was changed by adding low molecular weight salts at a fixed polyion concentration (C = 0.25 mol/L). To solve the controversy about the added salt effect on the characteristic maximum in small-angle scattering of polyelectrolyte solutions, separation of the total scattering function into the intra- and intermolecular parts has been performed. With increasing the ionic strength of the solution the maximum position qm in the total scattering function of SAXS and SANS slightly shifts toward the lower scattering vector and subsequently disappears, whereas the maximum position in the intermolecular scattering function slightly shifts to the higher scattering vector, but the peak itself does not disappear even for the highest ionic strength of the present study though it be...

Time-resolved light scattering measurements were performed on gelation processes of poly(vinyl alcohol) (PVA) solutions at 25 °C in mixtures of dimethyl sulfoxide (DMSO) and water (H2O) with volume ratios of 60/40 and 80/20. It was found that the scattering profile I(Q) from a 60/40 (DMSO/H2O) solution has a maximum whose position Qm is independent of time and that the intensity I(Q) at Q = Qm increases exponentially with time. These observations agree with the theoretical predictions for the initial stage of spinodal decomposition (SD) type phase separation, while the scattering profile I(Q) from a 80/20 solution has no peak. It is therefore concluded that the SD type microphase separation occurs before gelation in the 60/40 solution, but not in the 80/20 solution. On the basis of present, as well as past results, a possible mechanism of the gelation process for PVA solutions has been proposed.

Quasielastic neutron scattering experiments have been performed on polyisobutylene, trans-1,4-polychloroprene, and polyethylene in the energy range from 0.01 to 10 meV at temperatures far above the glass transition temperature T g and on cis-1,4-polybutadiene near Tg. Similar to the previously reported results on cis-1,4-polybutadiene far above T g , we observe in these polymers a slow process on a time scale from several tens to several hundreds of picoseconds which we term the E-process (or elementary process) as well as a fast process with a time scale of about a picosecond. We consider the relaxation time map of polybutadiene near and above the glass transition temperature to illustrate that the fast process is common for most glass-forming materials and that the E-process may be assigned to an elementary process involving local chain conformational transitions. Finally, we analyze the E-process in terms of a previously introduced jump diffusion model with damped vibrations, which is consistent with recent results of molecular dynamics simulations for bulk amorphous polymers, and we discuss the possible mechanism of the conformational transitions.

Aiming to clarify the mechanism of crystal nucleation of polymers, we have made a quantitative investigation about the conformational change of syndiotactic polystyrene (sPS) during the induction period (ca. 30 min) when crystallized at 120 °C, 25 K above the glass transition temperature Tg = 95 °C, from the glassy state, i.e., for the so-called glass crystallization by time-resolved Fourier transform infrared (FT−IR) spectroscopy. It was found that even in the induction period, the absorbance of trans conformation bands begins to increase and it continues to increase not only through the induction period but also after crystallization. This suggests that the length of rodlike segments consisting of trans sequences starts to increase in the induction period. In this connection, Doi's theory on the isotropic-to-nematic transition of polymer liquid crystals has predicted that the extension of these segments triggers the orientation fluctuations of the rod segments because the increase of their excluded volu...

Local chain dynamics of atactic polypropylene, a typical amorphous vinyl polymer, has been studied by both quasielastic neutron scattering and macroradical decay measurements by electron spin resonance to detect the fast process of picosecond order observed for most amorphous materials. It was found that the fast process sets in at the Vogel-Fulcher temperature T 0 , similar to observations for other simple polymers, suggesting that the fast process is a precursor of the glass transition. In coincidence with the onset of the fast process, the acceleration of the macroradical decay is also observed in the vicinity of T 0 , indicating a close connection of both phenomena. This is the first experimental evidence for the fast process from two independent measurements.

We have investigated the growth shape of two-dimensional (2D) poly(ethylene terephthalate) spherulites using a transmission electron microscope technique in order to examine the role of a diffusion-controlled mechanism in the growth process. At the growth front of the 2D spherulites, we found a terrace-like morphology having a single crystal structure. The growth front of the terrace shows instabilities of periodic or groove patterns which can be explained by the diffusion-controlled theory for crystal growth.

The effect of long-range density fluctuations on the primary (α-) relaxation in poly(methyl-p-tolylsiloxane) (PMpTS) was studied by means of light scattering. It is shown that the long-range density fluctuations (clusters) contribute only to the polarized (VV) and not to the depolarized (VH) correlation functions and make the system apparently nonergodic in the time scale of the α-process. Samples with different amounts of clusters were obtained by annealing at 55 °C for different time intervals in temperature jump experiments : +120 → +55 → -2.6 °C. The mean relaxation times and their distribution of the α-process obtained from the VH correlation functions (sample with clusters) and both VV and VH correlation functions (cluster-free sample) were equal and did not depend on the amount of clusters, indicating no coupling between the long-range density fluctuations and the primary α-relaxation.

The authors report small-angle neutron scattering (SANS) and light scattering (LS) studies on poly(vinyl alcohol) (PVA) gels formed in a mixture of deuterated dimethyl sulfoxide (DMSO-d{sub 6}) and heavy water at 23 C. It was reported in a previous paper that the SANS intensity I(Q) of the PVA gels is well described by the Ornstein-Zernike (OZ) formula I(0)/(1 + {zeta}{sup 2}Q{sup 2}) and Porod`s law Q{sup {minus}4} for 0.01 {angstrom}{sup {minus}1} < Q < 0.035 {angstrom}{sup {minus}1} and 0.05 {angstrom}{sup {minus}1} < Q < 0.1 {angstrom}{sup {minus}1}, respectively. In this work, the authors extended the Q range down to 3 {times} 10{sup {minus}3} {angstrom}{sup {minus}1} and found that I(Q) turns up for Q < 8 {times} 10{sup {minus}3} {angstrom}{sup {minus}1} to deviate from the OZ formula. This upturn has been assigned to structure due to phase separation based on the results of SANS and LS measurements. In order to investigate the gelation process, time-resolved SANS measurements were carried out on the PVA solutions after quenching to 23 C from 100 C. It was found that the correlation length {zeta} evaluated by the OZ formula in a Q range of 0.01--0.035 {angstrom}{sup {minus}1} is dominated by concentration fluctuations in the earlymore » stage of the gelation before crystallization (t < 200 min) while, after the crystallization initiates, the average correlation distance between the nearest-neighboring crystallites becomes a dominant factor in {zeta}. Distance distribution function P(r) which is defined by inverse Fourier transformation of the scattering intensity was calculated to see the size and the distribution of the crystallites.« less

On the basis of a new finding reported in previous studies that the structural formation in the induction period of crystallization involves a kind of phase separation of spinodal decomposition due to the orientation fluctuations of polymer segments, we have investigated the structural change of PET from a structure size point of view using a SAXS technique when it was crystallized at 80 or 5°C above the T g from a melt-quenched glass. A spatial density correlation analysis of the SAXS intensities reveals that the size of the dense domains caused by the density fluctuations in the induction period is fairly large compared with the lamellar thickness after crystallization, indicating that these dense domains are not the embryos predicted by the classic nucleation theory

The structure of poly(vinyl alcohol) (PVA) gels formed in a mixture of deuterated DMSO and heavy water at 23°C has been investigated. It was directly confirmed from the wide-angle neutron scattering measurements that cross-linking points or junction points in the gels are crystallites. In the small-angle scattering measurements, it was found that the scattering intensity I(Q) decreases with Q according to the -4th power law (Porod's law) in the Q range above 0.05 A -1 where Q=4π sin θ/λ (2θ and λ are scattering angle and wavelength of neutron, respectively), suggesting that the surface of the crystallites has a clear boundary

Local motions are investigated in the time range 10 −13 to 10 −10 s. Two modes are found in this time range. The faster and slower modes are assigned to damped vibrational motion and local conformational transition, respectively. The latter is analyzed in terms of a jump diffusion model with the damped vibrational motions on the jump sites. The observed conformational transition rate is compared with the Kramers' rate theory, and the spatial scales of the motions are discussed based on the molecular structure of cis-1,4-polybutadiene

Etude de solutions de polyhydrogenesulfate de vinyle et de ses sels de lithium, sodium et potassium

La transition entre la region diluee et la region semidiluee se produit a une masse moleculaire critique. Etude avec du polystyrenesulfonate de sodium sans addition de sel