In this paper, I introduce some kinds of measurement methods of mechanical properties of liquids utilizing electromagnetic interaction. In the conventional methods of viscosity measurement, almost all of the apparatus employ mechanical probes in touch with the sample materials, which is directly driven through the mechanical shaft. For the remote measurement of the rheological properties, my laboratory developed some methodology using electric and magnetic forces. First, I introduce the electric tweezers system to observe local mechanical information near the sample surface. A metal electric needle set just above the surface applies a local electric field, which slightly picks up the sample surface with the Maxwell stress. Second, I explain the high-speed measurement of the surface tension and the viscosity, in which a non-contact handling technique of the trajectory and shape of the flying micro liquid droplets are employed. Some related topics concerning the molecular dynamics are also given. Finally, the electro-magnetically spinning system is shown, in which an electrically conductive rotation probe is driven by inducing a temporally modulated magnetic field. Some industrial application utilizing the feature of remote sensing are also shown.

Coating workability is one of the most important requirements for paints. Namely, paints are demanded to exhibit no sagging after the coating process thereby allowing an easy operation to achieve good appearance of the paint films. Nevertheless, paints tend to exhibit a spatter in a fast roller-coating process, which requires a huge effort of protecting walls and floors with cover sheets and disturbs the easy operation. This spatter can be suppressed if paints are highly viscous, but the fast and easy operation is difficult for such paints. With this background, this study attempted to develop, from a rheological viewpoint, a high-performance paint free from this difficulty. Visual observation of the roller-coating process revealed that a paint thread formed between the roller and a substrate is stretched and then fragmented into droplets thereby giving rise to the spatter. Rheological analyses suggested that material parameters other than the viscosity, namely the storage modulus and first normal stress difference governing the elasticity of the thread, can be tuned to suppress the thread fragmentation and spatter without disturbing the easy operation. This rheological knowledge enabled development of spatter-less waterborne paints through a choice of additives optimizing the viscous and elastic properties of the paints.

I reviewed our studies of improvement of mechanical and optical properties in polymeric materials by addition of small-molecules based on orientation correlation and restriction of molecular local dynamics. Birefringence, which is one of important properties for optical applications, is induced by molecular orientation of polymer chains. In order to improve birefringence of stretched films by small additives, we investigated the orientation behavior of the additive molecules in polymer films during stretching based on the nematic interaction theory. We examined the modulus enhancement of polycarbonate (PC) by addition of rod-like small molecules. From the results of mechanical and dielectric relaxation measurements, the modulus improvement was caused by restriction of local dynamics of polymer and rotational motion of additives due to the filling the free volume of PC. Moreover, we found that, based on the photo-elastic theory, the enhanced modulus in PC reduced the photo-elastic birefringence, which must be decreased for optical films.

Rheological properties, especially shear thickening behaviors of high-concentrated slurries have been analyzed by using large amplitude oscillatory shear (LAOS) measurements. Concentrated slurries often exhibit shear thickening that is observed as viscosity increase with shear rate in addition to shear thinning as viscosity decrease with the shear rate. The LAOS measurement is useful for the analysis of these nonlinear rheological behaviors. In this study, we applied the LAOS measurement to two model slurries indicating continuous and discontinuous shear thickening behaviors and proposed new indices to quantitatively express the shear thickening/thinning and strain hardening/softening. These indices reflecting the phase and intensity of the third harmonic resulting from the Fourier transform of the time-dependent strain well described the continuous and discontinuous shear thickening.

In anticipation of that direct examination of the shear flow affection on the dynamic viscoelasticity might bring more comprehensive results than the LAOS method, a series of dynamic viscoelasticity measurements with parallel superposition of steady shear flow was planned. The measured values which are function of shear rate ̇γ, that is, storage and loss moduli G′(̇γ), G″(̇γ) and viscosity η(̇γ), are analyzed as three non-dimensional parameters G′(̇γ) / G′(0), G″(̇γ) / G″(0) and η(̇γ) / | η*(ω, ̇γ) |, where η* is complex viscosity.
A Couette rheometer ONRH-1b (OhnaTech) was employed, and for the samples, hydroxypropyl cellulose, xanthan gum, carboxyvinyl polymer and C24-hydrophobically modified ethoxylated urethane ware used.
All three analyzing parameters show clearly the differences of samples. It is found that the nature of their responses are subjected not by the shear itself, but by the value that divided shear rate with measure frequency (̇γ/ω). On the other hand, it is found that the properties that are subjected by the shear rate do exist. Observation of these results asserts that multifactorial rheological measurement including this superposition method is worthwhile.

Normalized extensional and shear viscosities, η_E/η_E0 and η/η₀ with the subscript “0” standing for quantities in the linear viscoelastic (LVE) regime, are theoretically analyzed for the FENE-dumbbell in the presence of isotropic friction-reduction under flow. The basic parameters in the analysis are the friction reduction factor r_ζ = ζ_sf/ζ_eq, FENE factor r_κ = κ_sf/κ_eq, and the Brownian force intensity factor r_B = B_sf/B_eq, with ζ and κ being the bead friction coefficient and spring strength of the dumbbell, B denoting the intensity of the Brownian force acting on the bead, and the subscripts “sf” and “eq” standing for the quantities under steady flow and at equilibrium, respectively: B_eq = 2ζ_eqk_BT with k_BT being the thermal energy, according to the fluctuation-dissipation theorem valid at equilibrium. The normalized viscosities were found to be analytically expressed as η_E/η_E0 = (r_B/r_κ){1−2(r_ζ/r_κ)Wi}⁻¹{1+(r_ζ/r_κ)Wi}⁻¹ and η/η₀ = (r_B/r_κ), with Wi being the Weissenberg number defined with respect to the LVE relaxation time. Both η_E/η_E0 and η/η₀ are proportional to the r_B factor, so that comparison of these quantities allows us to characterize the intensity of the Brownian force B_sf under flow. For example, for a test case of power-law decay of r_ζ with Wi, the above expressions of η_E/η_E0 and η/η₀ suggested a relationship 2ζ_sfk_BT < B_sf < 2ζ_eqk_BT
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