In this study, a novel statistical model on the ultrasonic irradiation dispersion has been developed. The model on the cluster break-up by ultrasonic irradiation was theoretically established with the ratio of ultrasonic power spent for the cluster break-up. The ultrasonic power was changed in three steps; 20, 40 and 60 W. The model estimation was compared with the experimental results. The experimental results show that the cluster size was found to take a certain asymptotic value for each irradiation power. With this steady state value, the ratio of ultrasonic power spent for the cluster break-up was determined. It was found that the ratio of ultrasonic power spent for the cluster break-up is very small and is proportional to the mean shear rate in the flow. The present model with this ratio was found well to evaluate the time-variation of the mean cluster size. Thus, the present ultrasonic dispersion model was concluded to estimate the effects of ultrasonic irradiation on the fine particle dispersion well.

Although chemistry dependence in the non-linear rheology of polymers has been rather established for uniaxial elongations, it has not been frequently discussed for fast shear. In this study, to see the effect of orientation-dependent monomeric friction on the shear rheology, we conducted primitive chain network simulations for a few poly(propylene carbonate) melts, for which we have determined the friction model from the uniaxial data recently [Yang et al., Nihon Reoroji Gakkaishi, 50, 127–135 (2022)]. The simulation qualitatively reproduced typical non-linear behaviors, such as shear thinning and stress overshoot, under fast shears. The agreement with experimental data became better when the friction was varied according to the segment orientation. In particular, the shear rate dependence of the peak position for the stress overshoot (i.e., the peak stress and the strain at the peak) was better reproduced. This result implies that chemistry-dependent friction may probably be discussed from the stress overshoot under high shear.

We derive the stress tensor of a rigid dumbbell by using the virtual work method. In the virtual work method, we virtually apply a small deformation to the system, and relate the change of the energy to the work done by the stress tensor. A rigid dumbbell consists of two particles connected by a rigid bond of which length is constant (the rigid constraint). The energy of the rigid dumbbell consists only on the kinetic energy. Also, only the deformations which do not violate the rigid constraint are allowed. Thus we need the dynamic equations which are consistent with the rigid constraint to apply the virtual deformation. We rewrite the dynamic equations for the underdamped SLLOD-type dynamic equations into the forms which are consistent with the rigid constraint. Then we apply the virtual deformation to a rigid dumbbell based on the obtained dynamic equations. We derive the stress tensor for the rigid dumbbell model from the change of the kinetic energy. Finally, we take the overdamped limit and derive the stress tensor and the dynamic equation for the overdamped rigid dumbbell. We show that the Green-Kubo type linear response formula can be reproduced by combining the stress tensor and the dynamic equation at the overdamped limit.

The thermal and flow behavior of nanofluids with rod-like particles in flows in a backward-step channel heated at its bottom wall was numerically analyzed. In the numerical simulations, the distribution of the volume fraction of nanoparticles was computed and both the viscosity and thermal conductivity were described as a function of the volume fraction. The viscosity and thermal conductivity of nanofluids were described by a model for suspensions of prolate spheroid particles and the Hamilton-Crosser model, respectively, and the translational diffusivity of nanoparticles was expressed by a model derived for rod-like macromolecules. The numerical simulations revealed that the average heat transfer coefficient was increased more by the addition of nanoparticles having a higher aspect ratio, whereas the power necessary for inducing nanofluid flow increased further. In addition, the increase in the average heat transfer coefficient saturated above a certain particle aspect ratio. It is therefore necessary to adequately select the nanoparticle shape and the volume fraction of particles in consideration of the trade-off between the improvement of thermal characteristics and loss of mechanical energy.

This study examined the validity of viscosity measurements in the frequency region of 10 MHz using a commercially available quartz crystal microbalance (QCM). Ethylene glycol aqueous solutions were used as model samples. From the changes in the resonant frequency and dissipation parameter before and after the introduction of the sample liquid, we determined dynamic viscosity through Johannsmann's equation and compared it with literature data for zero shear viscosity. As a result, the viscosity estimated by QCM was systematically higher. Based on the analysis of the electrical equivalent circuit of the resonator, we considered that such deviation is due to the energy loss inside the quartz resonator and the non-ideal nature of the interface in contact with the sample liquid. To avoid such non-idealities, we proposed a method of applying a calibration equation to the viscosity value obtained from the Johannsmann equation. This makes it possible to easily measure viscosity in the 10 MHz regions with an accuracy of ± 3 % error.

In this report, the 49th volume published last year (2021) is reviewed. The statistics show that the total number of published papers and the ratio of English manuscripts are 37 and 0.57, which are similar to the average of past volumes. The contents distribute among various fields of rheology. However, the distribution is not uniform and different from that observed in the meetings. For instance, in this specific volume, remarkable numbers of publications are seen on the topics related to polymer rheology, polymer processing, and computer simulations. Such a bias is due to the special issues and specific research groups that actively submitted their works to the journal.