Tatsuya Kawaguchi

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...

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 ...

Inelastic neutron scattering study of low energy excitations in glassy 1‐butene

Glassy 1‐butene (CH2=CHCH2CH3) was studied by incoherent inelastic neutron scattering below 10 meV in the temperature range 18≤T≤80 K covering the glass transition temperature (Tg=60 K). A broad excitation peak due to the low‐energy excitation was found at 3–4 meV. The spectra corrected for the Bose factor could be scaled to a unique curve for temperatures below Tg. The absolute density of vibrational states was derived from the spectrum at 18 K and the previously measured heat capacity data. The number of vibrational states associated with the low energy excitation was 1.4 per molecule. This is much larger than those for SiO2 and other amorphous materials studied so far. The density of vibrational states was well reproduced by the soft potential model originally conceived for network glasses.Glassy 1‐butene (CH2=CHCH2CH3) was studied by incoherent inelastic neutron scattering below 10 meV in the temperature range 18≤T≤80 K covering the glass transition temperature (Tg=60 K). A broad excitation peak due to the low‐energy excitation was found at 3–4 meV. The spectra corrected for the Bose factor could be scaled to a unique curve for temperatures below Tg. The absolute density of vibrational states was derived from the spectrum at 18 K and the previously measured heat capacity data. The number of vibrational states associated with the low energy excitation was 1.4 per molecule. This is much larger than those for SiO2 and other amorphous materials studied so far. The density of vibrational states was well reproduced by the soft potential model originally conceived for network glasses.

Genotoxicity of substances in the nightsoil and its biologically treated water

Genotoxicity was evaluated in the performance of nightsoil treatment plants, because the human feces and urine would contain some genotoxic compounds. A newly developed assay, Salmonella typhimurium NM strains in umu test, were applied to the samples to detect highly sensitive activities induced by nitroarenes and aromatic amines. Strong genotoxicity could be observed in the influent of a nightsoil treatment plant and the effluent from biological reactor by both of parent strain and new strains. The quantitative analysis using the genotoxic intensity, that is, the slopes of dose-response was conducted to compare the genotoxicity on a group of some compounds included in complex samples such as nightsoil. The genotoxicity on aromatic amines was converted to the potency by aminofluorene represented as mg aminofluorene/mg dry weight. The genotoxicity could not be removed by biological treatment process and ultra filtration, and reduced around 90% by coagulation-sedimentation process. While the potency on nitroarenes which was converted to 1-nitropyrene, mg nitropyrene/mg dry weight, could not be removed sufficiently through the treatment process.

Microscopic view of glass transition dynamics: A quasielastic neutron scattering study on trans‐1,4‐polychloroprene

We have studied the glass transition dynamics of trans‐1,4‐chloroprene from microscopic view points using a quasielastic neutron scattering technique in a time range of ∼4×10−13 to ∼4×10−10 s. It was found that the so‐called fast process of picosecond order appears at around the Vogel–Fulcher temperature T0, similarly to cis‐1,4‐polybutadiene having no large side groups [J. Chem. Phys. 98, 8262 (1993)]. It is considered that the onset temperature at around T0 must be characteristic to polymers having no large side groups or no large internal degrees of freedom. In addition to the fast process, the slow process of subnanosecond order sets in at around the glass transition temperature Tg and the activation energy of the relaxation time was found to be ∼2.5 kcal/mol. The nature of the slow process is discussed in terms of conformational transition near Tg.

Evaluation of toxic substances in effluents from a wastewater treatment plant

Abstract The experimental investigation of effluent from municipal wastewater treatment plants and nightsoil treatment plants was conducted from the viewpoint of safe effluent water quality to evaluate the strategies and regulations for wastewater reuse. A bacterial assay named umu-test, which can detect error-prone repair dependent on DNA damage by some chemicals, was applied to samples from treatment plants. Concentrates of secondary effluent of municipal sewage treatment plant revealed strong genotoxicity, and its activity could be observed every day of the week. Also, the samples from secondary effluent separated by ultrafiltration in a nightsoil treatment plant showed positive genotoxicity. Newly developed strains which are Salmonella typhimurium in umu-test are highly sensitive to aromatic amines and can detect the genotoxic activity induced by these compounds. By using this method, the genotoxic potency of above samples was examined. The toxicity on aromatic amines could be detected in the matter contained in raw nightsoil. This shows that human feces involve some genotoxic substances and the genotoxicity could not be reduced through the biological treatment with nitrification and denitrification, nor removed by the ultrafilter separation process. A coagulation-sedimentation process could partially remove the toxic substances from the solution and activated carbon adsorption could almost remove the substances. The liquid chromatography column was applied to fraction the concentrated substances to elute the toxic substances from samples. Some genotoxic fractions related to aromatic amines would be observed more clearly by this method. In order to reuse the effluent from the treatment plant of the very close side to human body, the reduction of those genotoxicities is expected from the viewpoint of human health. From the results of ozone application to the effluent, it was found that the genotoxicity could be clearly reduced to a negative level at the ozone consumption ratio of 1 mgO 3 consumed mgC .

Local dynamics of cis-1, 4-polybutadiene near the glass transition temperature Tg

Local dynamics of cis-1, 4-polybutadiene near the glass transition temperature T g (=170K) has been investigated by quasielastic neutron scattering in the energy range of 0.01 meV to 10meV. It was found that two models of motions appear near the T g in the energy range of ca. 1 meV and 10 ∽ 30 μeV. The fast mode arises ca. 50 K below T g which corresponds to the so-called Vogel temperature T 0 . On the other hand, the slow mode appears just above T g . The natures of the two modes are discussed from viewpoints of glass transition.

Fast relaxations of amorphous polystyrene

Abstract The local dynamics of amorphous polystyrene have been investigated by incoherent inelastic and quasielastic neutron scattering in a temperature range of 20 to 300 K, below the glass transition temperature T g ( = 373 K). The elasticscattering intensity shows an anomalous decrease at temperatures above 200 K. Corresponding to the anomalous decrease, the shape of the dynamic scattering law S ( Q,ω ) changes from inelastic-like to quasielastic-like, suggesting the onset of a fast relaxation process. On the basis of the results from hydrogenated polystyrene and polystyrene with a deuterated phenyl ring, the fast relaxation process occurring far below T g has been assigned to motion of the phenyl side chains.

Low energy excitation and fast motion near Tg in amorphous polymers

Abstract Dynamics of amorphous polymers have been studied below and above the glass transition temperature, T g , by inelastic and quasielastic neutron scattering technique in the energy range of 0.02 to 10 meV. All the amorphous polymers examined show a broad excitation peak, the so-called ‘low energy excitation’ peak, at 1.5–4 meV below T g , irrespective of differences in chemical structures. As temperature increases, neutron spectra become quasielastic-like (spectral softening) due to onset of a very fast motion of ps order. The fast motion appears at about 50 K below T g for cis-1,4-polybutadiene, which is close to the Vogel-Fulcher temperature, T 0 . On the other hand, atactic polystyrene (a-PS) shows the spectral softening at about 200 K, being about 170 K below T g . The origin of the spectral softening of a-PS was assigned to onset of side chain motion.

Influence of the microstructure on the incoherent neutron scattering of glass‐forming polybutadienes

This paper presents the first neutron scattering measurement of 1,2‐1,4‐polybutadienes with varying microstructure. Incoherent inelastic scattering experiments have been performed in the range of moderate (ΔE≊300 μeV) and high (ΔE≊20 μeV) energy resolution. For the moderate resolution experiments the vibration–relaxation model has been used as a guideline for interpretation. The most striking influence of the microstructure variation can be found in the position of the boson peak. Its position at low temperature as well as its temperature dependence is significantly different among the measured samples. The high resolution data have been Fourier transformed into the time domain yielding the intermediate incoherent scattering function in a time range of 5,...,150 ps. There, the basic properties found for 1,4‐polybutadiene earlier could be reproduced (separation of α and βslow regimes of the slow relaxation, Kohlrausch–Williams–Watts function with β≊0.4). On the basis of the new data, no microstructure indu...