Taichi Hirano

Electromagnetically Spinning Sphere Viscometer

We have developed a simple system for viscosity measurement in the range of 10-3 to 101 Pas. An aluminum sphere revolves in a sample cell under a rotating external magnetic field, and the rotational speed of the sphere gives the sample viscosity. Low viscosities can be measured by using a micro-probe sphere, since the viscous torque applied to the sphere overcomes the frictional force at a sufficiently small sphere radius. The system is free from contamination and can be easily applied to medical and biological studies.

Friction torque reduction by ultrasonic vibration and its application to electromagnetically spinning viscometer

The technology of using ultrasonic vibration to reduce friction was applied in our experiment to improve the accuracy of viscosity measurements. The electromagnetically spinning (EMS) viscometer we developed has a remarkable feature: the sample viscosity can be measured in an entirely noncontact manner. Although the apparatus enables low-viscosity measurements of less than 10 mPa·s, which has been difficult to achieve using conventional rotation viscometers, the accuracy has been limited to 10% because of the harmful effect of mechanical friction. We made a new EMS system equipped with piezoactuators to excite ultrasonic vibration to the sample cell, thereby successfully reducing the mechanical friction to one-third that in the previous system. A theory to describe the mechanical friction between the rotating probe and oscillating substrate was also proposed and examined in comparison with the experimental results.

Low-Viscosity Measurement by Capillary Electromagnetically Spinning Technique

We study sphere rotation against viscous torque confined in a small space. Our new invention, the electromagnetically spinning sphere (EMS) viscometer measures liquid viscosity through the observation of sphere rotation driven by electromagnetic interaction in a noncontact manner. The lower limit of the measurable viscosity is determined from the ratio between the viscous torque and the mechanical friction, and the apparent increase in the contribution of the viscous term leads to the improvement of the accuracy of low-viscosity measurement. We propose a theoretical expression of the torque applied to a sphere rotating in a cylinder and obtained the power law with respect to the gap in between. The results of the numerical simulation and experiment provide evidence of the validity of the theory.

Accurate Viscosity Measurement of Ethanol Solution for Determination of Ultrasonic Relaxation Parameters

We demonstrate the performance of a newly developed viscosity measurement system, especially designed for liquid samples with low viscosities. The electromagnetically spinning (EMS) viscometer operated with a floating disk rotor enables the determination of viscosity with 1% accuracy for dilute aqueous solutions of various materials. In the article, we report the concentration dependence of the viscosity of a water/ethanol mixture. Accuracy required for a viscometer from the viewpoint of ultrasonic spectroscopy is also discussed.

Accurate Viscosity Measurement using Disk-Type Electromagnetically Spinning System

We introduce an accurate viscosity measurement method that is especially effective for low-viscosity (<10 mPas) samples. The combination of an electromagnetically spinning system and a disk-type rotor remarkably reduces mechanical friction, thus making possible rapid, noncontact viscosity measurements with accuracy better than 1%. The influence of a large Reynolds number on viscosity measurement is also examined.

Induction of Orientational Order through Coupling with Hyper Shear Flow

We directly observed the molecular orientation induced by a hyper shear strain rate of 106 s-1 during the head-on collision of microdroplets. The magnitude of the induced orientational order can be almost equal to that in the nematic state with a spontaneous director. The actual orientational order estimated from microscopic images agreed with the anisotropy determined theoretically from our previous experiments.

Simple and accurate determination of sol–gel phase transition point using disk-type electromagnetically spinning viscosity measurement system

We performed viscosity measurements with ultrahigh sensitivity by combining our original electromagnetically spinning technique and a newly developed floating disk probe. This system is, in principle, a torque-control-type viscometer with a noncontact function that can apply an arbitrary low torque, and therefore, enables us to clearly distinguish between liquids and solids from the viewpoint of the mechanical property of materials. In our measurements, we examined the difference in the thermoreversible sol–gel transition of a methylcellulose solution to determine the precise transition points, and successfully observed the hysteresis behavior of the gelation and solation processes.

Gas viscosity measurement with diamagnetic-levitation viscometer based on electromagnetically spinning system.

Utilizing a graphite-disk probe attached with a thin aluminum disk, we have developed a friction-free viscosity measurement system. The probe is levitated above a NdFeB magnet because of diamagnetic effect and rotated by an electromagnetically induced torque. The probe is absolutely free form mechanical friction, and therefore, the accurate measurements of the viscosity of gases can be achieved. To demonstrate the accuracy and sensitivity of our method, we measured the viscosity of 8 kinds of gases and its temperature change from 278 K to 318 K, and we confirmed a good agreement between the obtained values and literature values. This paper demonstrates that our method has the ability to measure the fluid viscosity in the order of μPa ⋅ s.

Spontaneous Ordering of Spherical Particles by Electromagnetically Spinning Method

The authors propose a technique to arrange particles into a two-dimensional crystalline structure with an arbitrary lattice constant. The electromagnetically spinning (EMS) technique can apply parallel torques to spherical particles in a noncontact manner. Among the spinning spheres dispersed in a fluid, the interactions due to the electromagnetic and hydrodynamic effects are expected to work in an opposite manner, being attractive and repulsive, respectively. To discover the fundamental basis of the interactions, we investigated the details of the hydrodynamic effect both experimentally and by numerical simulations, and clarified the dependence of the repulsive force on hydrodynamic conditions.

Measurement of Rheological Properties under High Shear Rate Induced by Collision of Micro‐Droplets

A new experimental technique for the measurement of fundamental properties of fluids under high shear rate up to 106 s−1 has been developed. The dynamic behavior of colliding two micro‐droplets was directly observed with microscope in a stroboscopic method. The oscillation after the collision is regarded as a damping vibration and we obtained the surface tension and viscosity for water from the oscillation frequency and damping constant, which agree with the static values. The molecular orientation in liquid crystal particle was also observed in crossed polars. The transmitted light was observed at the moment of the collision even in the fluid particles of isotropic phase. The result indicates that the corporative orientational order is induced by the large‐amplitude shear flow through the coupling interaction between the molecular internal degrees of freedom.