On the occasion of receiving SRJ Distinguished Service Award for 2017, I record our activity and events for the enlightenment and the spread of polymer rheology, with my precious memories of the people involved.

Shear flow can change not only the structure of soft matter but also the nature of fluctuation and response by breaking the time-reversal symmetry. We constructed a system combining a rheometer and a confocal laser scanning microscope to observe three-dimensional structure under shear flow and measure shear stress at the same time. Here, we present our results. First, we investigated the structural change of an immiscible blend subjected to a step electric field under shear flow. The relation between the structural change and the transient shear stress was discussed in terms of the interface tensor charactering the orientation distribution of interfaces. Next, Brownian motion in a simple shear flow was investigated by using a new method for observation and analysis. We found that the mean-square displacement consists of an anomalous t³ term in addition to the normal Einstein diffusion term linear in t. Last, we investigated the linear response of shear stress to ac electric fields under shear flow in a nematic liquid crystal. Although the Debye-type response was obtained at low shear rates, discrepancies were observed at high shear rates. Nonconservative forces were found to play an important role in determining the fluctuation dynamics.

We have developed and commercialized novel polyurethane (PU) with high elasticity and durability based on a cycloaliphatic diisocyanate controlled the stereoisomer structure. The diisocyanate is called FORTIMO^TM trans-1,4-bis (isocyanatomethyl) cyclohexane (1,4-H₆XDI). FORTIMO^TM 1,4-H₆XDI controlled with high trans isomer structure forms a well-organized hard segment phase. Therefore a micro-phase separation structure between soft segment and hard segment phases is progressed, resulting in an improved elasticity and heat resistance of PU elastomer. In addition, the light stability for long term of this PU is excellent due to an aliphatic structure. FORTIMO^TM 1,4-H₆XDI based PU achieve superior elasticity and durability which was not able to be realized with the existing diisocyanate. FORTIMO^TM 1,4-H₆XDI is applicable to various PUs, for example, not only thermoplastic, thermoset PU elastomers, but also water dispersed PU, micro-cellar and flexible PU foam with these advantages. This paper will describe the concept and examples of application of FORTIMO^TM PU to industry.

Formation of polymer aggregates in solutions or gels can induce drastic changes of their rheological properties, and rheological measurements can elucidate the structure of polymer aggregates in solutions or gels. In this manuscript, some recent researches on thermal renaturation of a double helical polysaccharide (xanthan), which forms aggregates by unwinding and rewinding its double helices, gelation of poly(L-lactic acid) which forms a fibrous structure preventing solvent flow by complex crystals of PLLA and solvent molecues, and inter-polymer aggregation of a biocompatible polymer (poly(2-ethyl-2-oxazoline)) and poly(methacrylic acid) which is induced by the hydrogen bonds between these polymers, were summarized. In these researches, intrinsic viscosity, storage modules, and loss tangent of the samples were measured to obtain the rheological characteristics. By the results of these measurements and some other experiments, such as light scattering, X-ray diffraction, scanning electron microscopy, and infrared spectroscopy, the structures of the aggregates in solutions or gels were estimated.

We review coarse-grained models of meso-scale structures for dynamics and rheology in polymeric systems. Polymeric systems often exhibit hierarchically self-assmebled structures from micro-scale structures to macro-scale structures. The rheological behavior of polymeric systems reflect the dynamics of hierarchical structures. In meso-scale coarsegrained models, characteristic structures with characteristic time and length scales (such as the end-to-end vectors and density fields) are utilized as the basic units. Such coarse-grained models are useful both for numerical simulations and analyses of experimental data. In this article, we consider basic properties and applications of several meso-scale coarsegrained models developped by the author, including the dynamics models for calculation of rheological properties, the structural models for polymeric solids, and the models for block copolymer micelles.

Fluidity of complex fluids such as dilute polymer solutions and threadlike micelle solutions is highly affected by its inside structure. The complexity of the fluid is that a key factor affecting the fluidity can be different at each length scale. We have been trying to investigate effects of polymers on turbulent drag reduction. In order to extract effects of extensional rheology of polymer solutions on a turbulent flow, we use wall-free two-dimensional(2D) turbulence. 2D turbulence was visualized and analyzed by interference patterns of the flow and PIV analysis. Polymers were found from the results to induce vortex deformation, which prohibits the energy transfer in the 2D flow. The phenomena were significantly affected by a relaxation time of polymer solution. We also studied effects of mixed solution of polymers and threadlike micelles on fluidity and on a sedimentation phenomenon of latent-heat fine particles in a latent heat transportation system. At a certain concentration, the particles were highly dispersed for several days. Inner structures of the solution were measured by a dynamic laser scattering system, which indicated the combined effects of polymers and threadlike micelles.

Transient single relaxation time τ_SS of glassy polymers was evaluated by using a nonlinear single relaxation model during uniaxial compression processes in which the compression rate changed stepwise from ε_n1 to ε_n2. After the change of compression rate, stress showed an undershoot (ε_n1 > ε_n2) or an overshoot (ε_n1 < ε_n2) before reaching the same value as the constant-rate compression at ε_n2. After a decrease of compression rate, τ_SS increased monotonously to the steady value at ε_n2. When the compression rate increased, τ_SS showed a discontinuous increase right after the acceleration, then steeply decreased to the steady value at ε_n2. Transient values of τ_SS after a decrease of compression rate as a function of the nonlinear flow rate ε_η of the dashpot in the model were almost the same function as the steady value of τ_SS, which was almost inversely proportional to ε_η. After an increase of compression rate and also in the transient state under the constant rate compression, τ_SS (ε_η) showed a higher value than those in the steady flow state. This observation indicates that, when glassy structures are getting unstable due to deformation, the nonlinear flow requires larger stress than the steady flow.

Blood flow analysis in the coiled cerebral aneurysm using computational fluid dynamics (CFD) simulation has been conducted to evaluate the extent of blood flow stagnation leading to aneurysm occlusion. However, few studies have considered the non-Newtonian feature of the blood, which might be associated with flow stagnation and subsequent thrombus formation. The present study investigated the non-Newtonian effect of the blood on the extent of flow stagnation in the coiled aneurysm. Two patterns of CFD simulations of the blood flow in the aneurysm with realistic coil configurations were performed using the Newtonian and non-Newtonian models for comparison. Both models showed similar flow patterns in the coiled aneurysm. However, the Newtonian model remarkably underestimated the degree of shear rate reduction especially in the low shear rate region (< 5 to 20 s⁻¹ ), which is a known trigger of thrombus formation. This finding suggests that the non-Newtonian effect of blood should be considered for the analysis of blood flow stagnation, which leads to thromboembolic events in coiled aneurysms.

Analytical solutions for shear stress in large-amplitude oscillatory shear flow (LAOS), for continuum or molecular models, often take the form of the first few terms of a power series in the shear rate amplitude. For corotational models, we get this truncated series using the Goddard-Miller integral expansion (GIE). Our previous work shows that the best Padé approximants for this truncated series, and specifically for the corotational Maxwell model in LAOS, can agree closely with the corresponding exact solution. We observe this close agreement, even for the Padé approximant for the series truncated after the fifth shear stress harmonic. In this paper, we begin with the extension of the GIE truncated after the next, seventh, order in the shear rate amplitude [Phys. Fluids 29, 043101 (2017)], and we then explore its Padé approximants. We uncover its best approximant, the [2,4], and compare it with both the GIE and the exact solution [Macromol. Theory Simul. 24, 352 (2015)]. We use Ewoldt grids to show the stunning accuracy of the [2,4] approximant in LAOS. We quantify this accuracy with an objective function and then map this function onto Pipkin space. We find the [2,4] approximant (from the GIE truncated after the seventh order in the shear rate amplitude) to be a simple accurate expression for the shear stress in LAOS. Our worked examples illustrate how researchers can use our new approximant reliably. For this, we use the Spriggs relations to extend the Padé approximant to multimode.

Trans-1,4-bis (isocyanatomethyl) cyclohexane (1,4-H₆XDI) has been newly developed as a novel cycloaliphatic diisocyanate with a high symmetric chemical structure. The PUEs were prepared with 1,4-H₆XDI, polyesterpolyol as a long chain polyol and 1,4-butanediol (BD) as a chain extender. As the representative aromatic and aliphatic diisocyanates, 4,4′-diphenylmethane diisocyanate (MDI) and dicyclohexyl methane-4,4′-diisocyanate (H₁₂MDI) were also used as the control. As a result, it was revealed that 1,4-H₆XDI-based PUEs achieved high elasticity such as higher impact resilience, lower compression set, improved heat resistant, and good light stability which was not able to be realized with the existing diisocyanates. The reason is explained that the hard segment chains of the 1,4-H₆XDI-based PUEs crystallized well with formation of hydrogen bonds in the PUEs due to the symmetric structure of 1,4-H₆XDI. Thus, the 1,4-H₆XDI-based PUEs can provide superior properties such as mechanical and thermal properties and excellent light stability compared to existing diisocyanate-based PUEs by rheological evaluation.

Relationships among tiger-striped flow mark patterns appeared in injection moldings, molecular characteristics, especially molecular weight distribution of polypropylenes (PP) and rheological properties of PP/talc compounds have been investigated. Usual tiger-striped flow mark pattern observed on one side of injection moldings of PP/talc compounds shows alternately bright and dark areas in the direction of flow and the pattern on another side reverses different phase pattern with brightness. But the flow mark patterns of some PP/talc compounds are quite different from the usual one. Those flow marks on both side of injection moldings revealed same phase pattern and/or changed halfway from same phase pattern to different phase one. We guessed the different flow mark patterns appeared in the injection moldings would result from the different flow, “slip flow”, behaviors of flow front during the injection stage of injection molding process. We also found that the flow mark of PP/talc compounds composed of PP with wide molecular weight distribution had almost same phase pattern. Therefore, we speculated slip behaviors of flow front are thought to be correlated with the content of critical molecular weight (M_c) for PP and also proposed M_c content should de decreased below 1 wt% to improve flow mark of PP/talc compounds with same phase pattern.

The relationship between the yield like behaviors and macroscopic and microscopic structures of the colloidal gels, which are consisted by silicone oil, hectorite and PEO, are examined from the rheological property, the anisotropic optical property and the flow behavior. These colloidal gels exhibit the yield behaviors in the stress ramp test and another yield like behavior is also observed in the high shear regime. From the motion of the oil droplets observed by the high-speed microscope and result of the flow birefringence measurements, the occurrence of the first yield behavior would be caused by generation of the thin shear layer and the other layers do not change their macroscopic structure for a while. During the flow after the first yield behavior, some part of the sample in the flow field becomes viscous thickening suddenly and it causes a large-scale flow fluctuation. The high viscosity region spreads to a whole area and a whoop stress appears. In this state, the flow birefringence shows the similar behavior of the polymer fluids. Therefore, we thought that the macroscopic structure related to the second yield behavior includes the entanglement like polymer fluids.

Waste polymer is thought to show poor mechanical property because of chemical degradation. However, from our recent studies, we have found that the main reason of the poor mechanical property is physically degraded and we can regenerate the mechanical property as virgin level. And this physical degradation is thought to be caused from crystalline inner structure. In this study, we prepared various samples by changing molding and heat treatment conditions. We also evaluated the relationship between long period and thickness of amorphous layer in the crystal structure by SAXS measurement and mechanical properties by tensile measurement of these samples. From this study, we found good relationship between these properties.