Atsushi Nakamura

Raman Scattering Study during the Dehydration Process of Polyacrylamide Gel

Raman scattering experiment was carried out simultaneously with weight measurement during the dehydration process of polyacrylamide (PAAm) gel. Anomalies in the Raman spectrum were observed when the time dependence of the weight altered: around the first characteristic time, a shoulder emerged on the skirt of the low-lying diffusive central mode, and then around the second one, the shoulder changed into a peak (which resembled the boson peak commonly observed in glass) in addition to the disappearance of the central diffusive mode and an O–H stretching mode. The correlation between the spectral change and the time dependence of the weight demonstrated the effect of increase in the polymer chain interaction on the gels dynamical properties.

Microphase separation in dehydrated N-isopropylacrylamide/sodium acrylate gel

The first small-angle X-ray scattering (SAXS) measurements were carried out in order to examine the mesoscopic structure in the N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel. By the SAXS measurements, a prominent peak was found in the dehydrated gel around 0.026 A-1. Taking into account of the cross section magnitude against X-ray, the concentration fluctuation of Na+ ions was a probable candidate for making contrast for the SAXS profile, which depends on the distribution of the hydrophilic group. Therefore, it was concluded that the mesoscopic structure found in the present study is due to the hydrophilic domains in the dehydrated gel which capture the Na+ ions and the remnant water inside the gel.

Elastic Anomaly and Glass Transition in Dehydrated Egg White Gel

Evolution of the complex elastic stiffness of dehydrated heat-treated egg white gel (DHTEWG) was measured with increasing temperature, from -30 to +170°C, at the rate of 8°C/min. In the measurement, the real component of the complex elastic stiffness decreased markedly and the imaginary component showed a broad peak around the temperature where a thermal anomaly had been observed (Tg; 50°C); furthermore, the elastic loss tangent showed a sharp peak at higher temperatures. Because these characteristics are usually observed in noncrystalline polymers around the glass transition temperature, the occurrence of glass transition in DHTEWG around Tg was confirmed.

Raman peak in low-frequency region of dehydrated egg-white gel

A new low-lying Raman mode was found in dehydrated heat-treated egg-white gel. The peak position and spectral profile were similar to those observed in polyacrylamide gel. The new mode may be the boson peak which is commonly observed in amorphous materials.

Low frequency Raman peak and elastic anomaly of dehydrated heat-treated egg-white gel

Abstract The viscoelastic stiffness of dehydrated heat-treated egg-white gel (DHTEWG) was measured with increasing temperature. The storage modulus decreased remarkably and the loss modulus showed a broad peak around the temperature where a thermal anomaly had been observed. Because these features are usually observed in the noncrystalline polymers around the glass transition temperature, the occurrence of the glass transition was confirmed in DHTEWG around Tg, which meant that DHTEWG could be regarded as a glass. Moreover, we also observed the low frequency Raman spectra of dehydrated egg-white (DEW) without the heat treatment and compared with those of DHTEWG. From this investigation, a notable difference has been revealed in the low-lying band frequency; in DEW, it was approximately the same as that of the boson peak reported on many amorphous materials or glasses, on the other hand, in DHTEWG, the frequency was 2–3 times as much as that value.

Change in the Low-Lying Raman Scattering Spectrum in the Glass Transition of Dehydrated Polyacrylamide Gel

The low-lying Raman scattering spectra were observed in the glass transition of a dehydrated polyacrylamide (PAAm) gel after examination of the transition by the differential scanning calorimeter (DSC) measurement. With increasing temperatures, a marked decrease in the scattering intensity of the Boson peak was observed. However, the peak could be still distinguished at temperatures much higher than the glass transition temperature. This feature could be due to the cross-linking of the polymer chains in the gel.

Evolutions of low-frequency Raman scattering spectrum, thermal and elastic properties of dehydrated polyacrylamide gel with increasing temperature

Abstract Dehydrated polyacrylamide gel was investigated by measuring Raman spectrum, thermal and elastic properties with increasing temperature. The elastic stiffness showed remarkable change around the temperature where a thermal anomaly occurred (Tg), demonstrating occurrence of the glass transition at Tg. However, a low frequency Raman peak could be still distinguished even far above Tg, indicating the complex structure of the network and solvent in the dehydrated gel.

Difference in Low Frequency Raman Spectra between Dehydrated Egg White and the Dehydrated Heat-Treated Gel

Low frequency Raman spectra of dehydrated egg white (DEW) and dehydrated heat-treated egg white gel (DHTEWG) were investigated in order to distinguish characteristics spectroscopically. A notable difference has been revealed in the low-lying band frequency; in DEW, it was approximately the same as that of the boson peak reported on many amorphous materials or glasses, on the other hand, in DHTEWG, the frequency was 2~3 times that in the conventional ones. This feature was considered the result of the crosslink of the polymer network in DHTEWG formed before dehydration.

Low-energy excitation in dehydrated gel

Abstract A low-energy excitation of dehydrated PAAm gel has been observed in the Raman and inelastic neutron-scattering measurements. The low-lying mode in the dehydrated gel could be distinguished even far above the glass-transition temperature with remarkable intensity decrease.

Structure Investigation of Metal Ions Clustering in Dehydrated Gel Using X-ray Anomalous Dispersion Effect

The structure of copper ion clusters in dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel has been studied by means of small angle X-ray scattering (SAXS) method. In order to distingui...