Toshiji Kanaya

Structural formation of poly (ethylene terephthalate) during the induction period of crystallization: 1. Ordered structure appearing before crystal nucleation

Abstract A new finding is reported concerning some structural change in the amorphous state of the polymer which occurs during the so-called induction period before the start of crystallization. Annealing of poly(ethylene terephthalate) (PET) at 115°C, or 40°C above the glass transition temperature, Tg, has been investigated by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. At a very early stage of the induction period the SAXS intensity starts to increase in the range of Q = 0.02–0.04 A −1 , where Q is the length of the scattering vector (Q = 4π sin θ/λ), and continues to increase until the beginning of crystallization. Corresponding to the initation of crystallization, another strong peak, caused by the usual long-period structure, appears in the vicinity of Q = 0.05 A −1 . It is confirmed from the WAXS measurements that no local ordering takes place during the induction period. To clarify the crystallization process, distance distribution analysis is also carried out.

Structural formation of poly(ethylene terephthalate) during the induction period of crystallization: 2. Kinetic analysis based on the theories of phase separation

Abstract Crystallization processes of poly(ethylene terephthalate) (PET) when annealed at 80°C, or 5°C above the glass transition temperature, Tg, have been investigated by a small-angle X-ray scattering (SAXS) technique. At a very early stage of annealing, a scattering maximum appears at around Q = 0.04 A −1 , where Q is the length of the scattering vector (Q = 4π sin θ/λ). During the so-called induction period of crystallization, this maximum intensity increases with annealing time and the maximum position shifts towards the low Q side. These results confirm the previously reported new finding that the long-range ordered structure is formed in the induction period before crystallization. These ordering processes can be divided into two stages: an early and a late stage. The scattering behaviour in the early stage is in accordance with the prediction of Cahns linearized theory for spinodal decomposition. The scattering profiles in the late stage can be described in terms of Furukawas scaling theory for the cluster growth regime. From these experimental results, we conclude that the growth process of the density fluctuation occurs in the induction period and this process is very similar to the spinodal decomposition type of phase separation process. It is considered that after this dense domain grows to a certain size, crystallization begins.

Determination of intrinsic viscosity of polyelectrolyte solutions

Abstract Intramolecular hydrodynamic contribution ηintra/C to the reduced viscosity ηSP/C of polyelectrolyte solutions is derived as a function of polymer concentration C by separating the theoretically calculated intermolecular electrostatic contribution ηinter/C from the observed reduced viscosity, assuming an additivity, ηSP/C=ηintra/C+ηinter/C. The resulting intramolecular part ηintra/C reflects nearly the net effect of the polyion conformation; it increases monotonously with decreasing polymer concentration and levels off to a constant in sufficiently dilute concentrations. The leveling-off value of ηintra/C corresponds to the intrinsic viscosity [η]. From the estimated values of [η], the ionic strength I dependence of the polyion conformation has been visualized, resulting in a similarity between two relations, ηintra/C vs. C and [η] vs. I.

Late stage dynamics of phase separation processes of binary mixtures containing surfactants

Late stage dynamics of phase separation processes of immiscible binary mixtures containing surfactants (amphiphilic molecules) is investigated by computer simulations on the hybrid model proposed by the present authors [T. Kawakatsu and K. Kawasaki, Physica A 167, 690 (1990)]. With use of this hybrid model, one can investigate large scale phenomena while retaining the intramolecular structures of surfactant molecules. Simulations are performed both for irregular bicontinuous and micellar domain formation processes taking the thermal fluctuation effects into account. In the very late stage, the coarsening of the domain structures is considerably slowed down both for bicontinuous and micellar domain formation processes due to the low interfacial tension of the surfactant–adsorbed interfaces. Scaled scattering structure functions are also calculated, which possess the characteristic features of the experimentally observed scattering functions of microemulsions and polymer blends containing amphiphilic block ...

Low-energy excitations in amorphous polymers

In order to investigate low‐energy excitations below 10 meV, inelastic neutron‐scattering measurements have been carried out on various organic amorphous polymers at 10 and 50 K and three inorganic glasses at 150 and 295 K. It was found that a broad excitation peak is observed for all amorphous materials in the ω range of 1.5–4.0 meV irrespective of different chemical structures. On the other hand, highly crystalline polyethylene with a degree of crystallinity 0.96 shows no such broad peak, indicating that the low‐energy excitation is characteristic of amorphous materials. We have employed an asymmetric double‐well potential as a common origin for the low‐energy excitation in amorphous materials and analyzed the results of amorphous polyisobutylene to confirm validity of this model and alternatively to determine parameters of the potential. Analysis of the temperature dependence of the inelastic‐scattering intensity of the low‐energy excitation leads to a concept of phonon‐assisted tunneling in the asymmetric double‐well potential.

Gels of poly(vinyl alcohol) from dimethyl sulphoxide/water solutions

Abstract Sol-gel diagrams of atactic poly(vinyl alcohol) (at-PVA) in a mixture of dimethyl sulphoxide and water (60/40 vol/vol) have been investigated. The crosslinking points of the gels are crystallites of PVA. Gelation of seven samples of at-PVA having degrees of polymerization (Pn) ranging from 186 to 20 200 was observed at quenching temperatures (TQs) between −60°C and 80°C. Gelation time, which is defined as time required for gelation, decreases with decreasing TQ. In a temperature range below ∼ −20°C, the gels are transparent and the critical gelation concentrations ( C∗ s ) are independent of TQ for all the samples except the lowest Pn. Further, C∗ s in this temperature range are proportional to P−0.5n, suggesting that C∗ is determined by the polymer chain overlap concentration. On the other hand, gels formed above −20°C are not transparent, and the degree of transparency decreases with increasing TQ. The lowest C∗ which is lower than the overlap concentration for polymer chains with radius of gryration Rg is observed in the TQ range of −20 to 40°C. This may be explained by the effect of liquid-liquid phase separation or spinodal decomposition, which is supported by TQ and PVA concentration dependences of u.v. transmission.

Fast process of amorphous polystyrene below and above the glass transition temperature Tg as studied by quasielastic neutron scattering

The dynamics of atactic polystyrene (PS) has been studied by a quasielastic neutron scattering technique in a temperature range of 21–475 K covering the glass transition temperature Tg (=373 K). The so‐called fast process in picosecond order is observed similarly to other glass‐forming materials in supercooled states so far reported. However, the onset temperature of the fast process is ∼170 K below Tg in PS, which is far below Tg in contrast to the previous observations. This result implies that the fast process is not necessarily the β process predicted by the recently noted mode coupling theory. By comparing the result of hydrogenated PS with that of partially deuterated polystyrene (PS‐d5) where only phenyl rings were preferentially deuterated, the origin of the fast process occurring far below Tg has been assigned to librational motion of phenyl rings, which is coupled with main chain motion near Tg. Analysis of the spectra by curve fit has suggested that the nature of the fast process changes at a t...

Loosening xyloglucan accelerates the enzymatic degradation of cellulose in wood.

In order to create trees in which cellulose, the most abundant component in biomass, can be enzymatically hydrolyzed highly for the production of bioethanol, we examined the saccharification of xylem from several transgenic poplars, each overexpressing either xyloglucanase, cellulase, xylanase, or galactanase. The level of cellulose degradation achieved by a cellulase preparation was markedly greater in the xylem overexpressing xyloglucanase and much greater in the xylems overexpressing xylanase and cellulase than in the xylem of the wild-type plant. Although a high degree of degradation occurred in all xylems at all loci, the crystalline region of the cellulose microfibrils was highly degraded in the xylem overexpressing xyloglucanase. Since the complex between microfibrils and xyloglucans could be one region that is particularly resistant to cellulose degradation, loosening xyloglucan could facilitate the enzymatic hydrolysis of cellulose in wood.

Low-energy excitation and fast motion near Tg in amorphous cis-1,4-polybutadiene

Dynamics of amorphous cis‐1,4‐polybutadiene was studied by incoherent inelastic and quasielastic neutron scattering below 10 meV in a wide temperature range covering the glass transition temperature Tg. The spectra at low temperatures below Tg show a broad excitation peak at about 2–3 meV, which is the so‐called low‐energy excitation and believed to be an origin of anomalous thermal properties of amorphous materials at low temperatures. It was found that the temperature dependence of the low‐energy excitation intensity can be normalized by the Bose factor at temperatures low enough below Tg. With increasing temperature, a very fast motion appears in the energy range below ∼4 meV at around the Vogel–Fulcher temperature T0, which is ∼50 K below Tg. This fast motion is often interpreted as the β process predicted by the mode coupling theory. In this paper, both the low‐energy excitation and the fast motion were analyzed in terms of a common microscopic picture, i.e., an asymmetric double well potential. The ...

Dynamics in the Glassy State and Near the Glass Transition of Amorphous Polymers as Studied by Neutron Scattering

This review covers the recent progress of studies on dynamics in the glassy states and near the glass transition of amorphous polymers as revealed by inelastic and quasielastic neutron scattering, covering four topics: (i) low energy excitation (boson peak) in the glassy states; (ii) fast process in picosecond order; (iii) E-process related to conformational transitions; (iv) dynamical heterogeneity as revealed by non-Gaussian parameter.