Hiroyasu Nomura

Effect of ultrasonic frequency on polymerization of styrene under sonication

The effect of ultrasonic frequency on polymerization of styrene under sonication at 50 degrees C was studied at the frequencies of 23.4, 45.7, 92, 518 kHz and 1 MHz. Polymerization under sonication was carried out at the ultrasonic intensity that gives the same reaction rate of decomposition of porphyrin. The magnitude of the polymerization rate increases in the order of 92, 45.7 and 23.4 kHz. At the high frequencies of 518 kHz and 1 MHz, no polymerization was observed. These facts mean that there is an optimum frequency in the range from 92 to 518 kHz for effective polymerization. The average-number molecular weights at the sonication time of 3 h are 5.5 x 10(4), 8.0 x 10(4) and 11.5 x 10(4) for the irradiated frequencies of 92, 45.7 and 23.4 kHz, respectively. Sonication for 3 h at 92 kHz gives polystyrene with very high polydispersity, about 5.0, in comparison with the results obtained at 23.4 and 45.7 kHz. These observations indicate that polymerization under sonication is influenced by the irradiated frequency.

Dynamics and hydration of trehalose and maltose in concentrated solutions

Viscosity, dielectric permittivity spectra and ultrasonic velocity in the aqueous solutions of trehalose and maltose were measured as a function of their concentration and temperature. The dielectric relaxation and ultrasonic relaxation were observed and were assigned to the structural relaxation. The values of viscosity and relaxation time of trehalose solutions are larger than those of maltose. The differences in the relaxation time for the two saccharides were discussed in terms of the larger hydration number of the trehalose.

Simple quantification of ultrasonic intensity using aqueous solution of phenolphthalein.

Aqueous phenolphthalein solution under sonication was investigated for use as a chemical dosimeter. The fading time of aqueous phenolphthalein solution under sonication depended on the concentration of phenolphthalein and the pH values of solutions. The fading time was correlated to the ultrasonic intensity in a reaction vessel that is estimated on the basis of decomposition of porphyrin. The relation between the fading time and the ultrasonic intensity for different frequencies is expressed by a single curve. From these results, it is indicated that aqueous solutions of phenolphthalein is useful for simple quantification of ultrasonic intensity for practical use, and one can regard it as one of the ultrasonic intensity indicators.

Effect of sonication on nitroxide-controlled free radical polymerization of styrene.

Effect of sonication on the autopolymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidinyl-1-oxy as the mediating radical was investigated at 110-135 degrees C. The thermal polymerization under sonication proceeded in the manner of a living radical polymerization to afford well-defined polystyrene. The sonication was found to decrease the induction period and increase the polymerization rate.

Ultrasonically induced birefringence in polymer solutions

For ultrasonically induced birefringence in polymer solutions, both the linear sinusoidal birefringence and the nonlinear stationary birefringence were observed. The sign and value of the stationary ultrasonically induced birefringence depended on the molecular structure of segment and its anisotropy in polarizability. Furthermore, no molecular weight dependence could be observed above the molecular weight 104. The theory based on the viscoelastic ones using the Rouse-Zimm model could not explain our experimental results as a whole. These results strongly suggest that the stationary ultrasonically induced birefringence should be caused by the local segmental motion of polymer chain in solution. For all polymer solutions investigated here, the stationary birefringence per ultrasonic intensity decreased with increasing frequency. This frequency dependence is not consistent with the present treatment for the ultrasonically induced birefringence.

Morphology and Sound Velocity of Plasticized Polyvinylchloride Studied Using Scanning Acoustic Microscope

Morphology and sound velocity of plasticized polyvinylchloride were studied using scanning acoustic microscope. Pseudonetwork and well-dispersed domains were observed as acoustic images. The sound velocity of leaky surface skimming compressional waves in the two domains and the intermediate domain were evaluated by analysis of the V(z) curves. The sound velocity in the well-dispersed domains was faster than that in the pseudonetwork domains.

Linear and Nonlinear Ultrasonically Induced Birefringence in Polymer Solutions

Ultrasonically induced birefringence in polystyrene-toluene solution was measured as a function of intensities. The birefringence signal was observed by the nonbiased and biased detection techniques. The values of birefringence obtained by the nonbiased detection technique were proportional to the ultrasonic amplitude, that is, the square root of the ultrasonic intensity and their intensity dependence was in accordance with those obtained by Jerrard (Ultrasonics 2 (1964) 74). The birefringence signal was successfully observed by the biased detection technique and its value was proportional to the square of the ultrasonic amplitude, that is, the ultrasonic intensity. In polymer solutions, two types of birefringence were induced; one was due to linear and the other was due to nonlinear origins.

Rapid and Precise Measurement System for Ultrasonic Velocity by Pulse Correlation Method Designed for Chemical Analysis

We developed an automatic measurement system for ultrasonic velocity in the megahertz region particularly designed for materials science. The ultrasonic pulse method is fully supported by digital equipment and the correlation function of the 1st and 2nd pulse echoes is numerically obtained from the ultrasonic velocity precisely determined to a relative accuracy of 10-6. An ultrasonic corner reflector is also employed to realize the high reproducibility of the measurement without adjusting the parallelism of the countering transducer and reflector. The performance of the system is examined by determining the concentration dependence of sound velocity in an electrolyte solution in a dilute range.

Effect of chain structure and molecular weight on ultrasonically induced birefringence in polymer solutions

Abstract Ultrasonically induced birefringence in polystyrene(PS)-toluene and polycarbonate(PC)-chloroform solutions was investigated using biased detection technique, by which the stationary birefringence can be detected. The sign of the birefringence signal was positive for PS solutions but negative for PC solutions. At molecular weight smaller than 1×10 4 , stationary birefringence observed in PS solutions increased with increasing molecular weight but no molecular weight dependence was observed when it was larger than 1×10 4 . The results are discussed in terms of the polymer chain dynamics in solutions.

Measurement of Ultrasonic Velocity of Hydrogels in Low-Temperature Region

The temperature dependence of the ultrasonic velocities in the temperature range from 15 to -55°C was measured for the agarose and methylcellulose hydrogels with different water content. The velocity jump was observed due to the freezing of the free water and it decreased with a decrease in water content. The temperature dependence of the ultrasonic velocities below the velocity jump temperature was discussed.