The composite technology is very important for production of high-functional or high-quality materials and products. We have studied the composite technology in processing of polymers and glasses. In this paper, I mainly present the research topics of mixing process of polymeric materials and multi-layered process of polymer films. For the mixing process of polymeric materials, we have developed the computer simulation techniques to predict the materials behavior in a twin-screw extruder and have proposed the methods to evaluate the mixing performance in melt mixing based on the simulation results. Such techniques and methods were applied to the melt mixing in engineering problems. For multi-layered process of polymer films, we have developed the simulation techniques of multi-layered flow for viscoelastic fluids and discussed the unstable problem and encapsulation phenomena at interface from the case studies considering die configurations, rheological properties, etc. The neck-in phenomena of multi-layered film could be also understood from simulation results in a die. We also studied the method to evaluate viscoelasticity of interfacial layer for multi-layered film using the parallel plate rheometer experimentally. We proposed the non-stick length of interface as an evaluation index. For processing of glasses using polymer-inorganic composites, we proposed processing method to give functions to glass products by using the formable polymer-inorganic composit as a precursor.
Well-controlled molecular design of supramolecular polymer gels, which can be prepared by incorporating noncovalent cross-links strategically, was proposed. In fact, supramolecular polymer gels were prepared by blending poly(2-vinylpyridine)-b-poly(ethyl acrylate)-b-poly(2-vinylpyridine) triblock copolymer (V-EA-V), poly(4-hydroxystyrene) homopolymer (H), and a nonvolatile ionic liquid (IL), where the two polymers were synthesized via reversible addition fragmentation chain transfer polymerization. The supramolecular polymer gels contained an IL as a solvent; therefore, they were called supramolecular/supramacromolecular ion gels. The supramolecular ion gels represented gel-like behavior at lower temperatures whereas they flowed within a normal timescale (several seconds) at higher temperatures. Such behavior was found to be thermoreversible. Master curves prepared from frequency-dependent viscoelastic spectra on the basis of time-temperature superposition principle exhibit the plateau modulus with approximately 10 orders of magnitude in reduced frequency. It was also revealed from temperature dependency of shift factors that the longest relaxation time at a low temperature such as 50°C was as long as 109s. Decrement of shift factors at lower temperatures was smaller than that of shift factors at higher temperatures. This is because the origin of relaxation is formation/dissociation of hydrogen bonds. When the concentration of H in solution blends was varied and that of V-EA-V was kept almost the same, the temperature at G' = G" (TG'=G") increased with an increase in H concentration. The sharpness of the change in G' against the temperature near TG'=G" depends on the phenol/pyridine stoichiometric ratio and the number of branches of V end blocks from one H polymer. Furthermore, it was also revealed from small angle X-ray scattering measurements that supramolecular gelation/supramolecular cross-linking was associated with formation of nanophase-separated structure. Knowledge acquired here is useful for development of novel/functional soft materials and analysis/interpretation of viscoelastic behavior of such materials.
Applicability of a bi-directional magnetic field is investigated on lowering the temperature of hot spots formed on the surface of a porous macrophage plaque typical of stenosis arteries. Having assumed that the blood obeys the Carreau model for shear-thinning fluids, the governing equations are derived for a two-dimensional, partially-constricted channel representing a stenosis artery. Treating the macrophage layer as a heat source, the coupled Cauchy, Brinkman-Forchheirmer, energy, and Maxwells equations are numerically solved using the finite-volume method based on the SIMPLE and ADI algorithms. The main objective of the work is to investigate the combined effect of electromagnetic force, the physiological parameters of the blood, and the geometrical properties of the constriction on the temperature distribution along the plaque’s surface. Based on the numerical results obtained in the present work, the shear-thinning behavior of the blood is predicted to play a negative role as it increases the temperature of the hot spot. A bi-directional magnetic field can lower the temperature of the hot spot (say, by roughly 0.4°C) through suppressing vortex formation in the rear side of the plaque. The magnetic field is also shown to lower the wall shear stress distributions on the lee side of the plaque.
It is known that conventional crystalline rice batter without gluten does not keep high void fraction after fermentation. In this study, the rice batter with amorphous rice flour provided a higher void fraction than that without amorphous rice flour. The void fraction of the rice batter increased with increasing content of amorphous rice flour. The uniaxial elongational property of the batter without amorphous rice flour did not show a strain hardening. On the other hand, addition of amorphous rice flour caused a strain hardening behavior in uniaxial elongational measurement. When amorphous rice flour content exceeded 60 wt%, we observed a strain hardening for the rice batter.
We report the stress relaxation behavior of a highly entangled polyisobutylene (PIB) melt in shear and uniaxial elongation. In shear the damping function of the PIB melt agrees well with the Doi-Edwards (DE) prediction when an adhesive is applied to avoid a slip at the sample-fixture interface. The damping function in uniaxial elongation also agrees with the DE prediction. However, the PIB melt shows a stronger damping in shear than the DE prediction when no adhesive is used. In the transient zone before reaching to the preset strains for stress relaxation the stress growth curve for the melt without adhesive coincides with the curve for "with-adhesive" at small strains, but branching from the growth curve for "with-adhesive" occurs at a certain strain.
In the present work, the effect of a fluid’s yield stress is investigated on the hydroelastic instability in pressure-driven flow through a two-dimensional channel lined with a highly-compliant polymeric gel. Having assumed that the fluid obeys the Herschel-Bulkley model with the gel obeying the two-parameter Mooney-Rivlin model, analytical basic solutions were obtained for the fluid and solid sides at vanishingly-small Reynolds numbers. The stability of the basic solutions so-obtained was then investigated when subjected to infinitesimally-small, normal-mode perturbations. Having dropped all nonlinear perturbation terms, an eigenvalue problem was obtained which was numerically solved using the shooting method. The effect of the fluid’s yield stress was then examined on the growth rate of the most unstable modes. Based on the numerical results obtained in this work, it is concluded that the yield stress has a destabilizing effect on pressure-driven flows of Bingham fluids in two-dimensional channels lined with compliant gels. For Herschel-Bulkley fluids, the effect of yield stress can be stabilizing or destabilizing depending on the power-law exponent (i.e., the degree of the fluid’s shear-thinning).
A Clapeyron-type equation to estimate the thermodynamic properties of the volume phase transition under load have been derived on the basis of the triphasic equilibrium. The expression for the coefficient of performance is also derived for the transition process. Experiments by using a poly(N-isopropylacrylamide) gel are made to investigate the detailed nature of the volume phase transition of the gel under tension. The coefficient of performance at the transition process for the gel increases with increasing tension and is analyzed by the Clapeyron-type equation presented.
The effects of added sugar on the transition entropy for the sol-gel transition of k-carrageenan and gellan hydrogels were examined. The sol-gel transition temperature (Ttr) for the hydrogels under load was determined using a laboratory-made apparatus and the transition entropy was evaluated from a Clapeyron-type equation. It was obtained that the transition entropy per unit gel volume (ΔSV) for the k-carrageenan gels remained constant, regardless of the species and concentration of added sugars, although Ttr was obviously influenced by these factors. Similar effects of added sugar were obtained for the gellan gels. These results suggest that the structure of crosslink domains of the gel just before melting is independent of the species and concentration of added sugars, provided the polysaccharide is given. In addition, ΔSV for the k-carrageenan and gellan hydrogels were almost constant regardless of the added species, sugar or salt.
Large deformation, nonlinear stress relaxation behavior was examined for poly(vinyl chloride) in di-isononyl phthalate (PVC/DINP) system having PVC content of 45.5 wt% at 180, 190, and 200°C. The PVC/DINP system exhibited power law type relaxation modulus, G(t, γ) ∝ t-n’, over a wide range of time t. The slope n’ increased with elevating temperature T irrespective of step-strain γ. At 190°C, the n’ value of the system was 0.75 showing a critical gel temperature (Tgel), because 0.75 was in agreement with the values obtained from the linear dynamic viscoelasticity reported previously. Time-strain separability G(t, γ) = G(t)h(γ) is applicable over a wide range of t. Here, G(t) is linear relaxation modulus. The magnitude of damping depended strongly on T. Below Tgel, in other words, in a gel state, h(γ) exhibited very weak strain dependence like cross-linking rubbers. In a critical gel state, the magnitude of damping was a little larger than that for the gel state. Above Tgel, in a sol state, h(γ) showed still more stronger strain dependence similar to branch polymers. It was found that h(γ) of PVC/plasticizer system strongly depended on temperature near Tgel.