Some topics in nonlinear rheology are discussed for polymeric systems: constitutive equation for dilute solutions; strain hardening in elongational flow; chain retraction in entangled systems; stress overshoot of non-entangled systems; entanglement molecular weight.

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Zero-shear viscosities η₀ of aqueous solutions of sodium hyarulonate were compared with the fuzzy-cylinder model theory, a typical theory for semiflexible polymer solutions. Taking into account electrostatic contributions to the chain-stiffness and excluded-volume effect, the theory quantitatively describes the concentration dependence of η₀ at molecular weights lower than 10⁶. On the other hand, the theory predicts too strong concentration dependence of η₀ at molecular weights higher than 10⁶ at high polymer concentrations. These results indicate that the flexible-chain dynamics (e.g., reptation motion), neglected in the fuzzy-cylinder model theory, are not important in solution viscosity for lower molecular weight sodium hyarulonate, but become important with increasing the molecular weight.

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Since the micro-structure of sintered film of ceramics strongly depends on the geometrical distribution of particles and the interparticle attractions in slurry, it is important to control the rheological properties of ceramic slurries for formation of thin sintered film with high density. The relationship among the rheology of slurries, film forming properties, and micro-structure of sintered film were studied to establish the technology of producing thin ceramics films by casting and sintering. The rheological properties of PZT slurries were controlled by the additions of surfactant and binder polymer. The polymer chain may attach to the surface at many points and not be able to desorb simultaneously from all sites. Hence, bridging flocculation is essentially irreversible in ordinary conditions. When the polymers do not have strong affinity for the particle surface, the adsorption-desorption and reversibly takes place by thermal energy. Therefore, the slurries behave as liquids at long times. The sintered films of PZT(lead zirconate titanate) at a thickness of about 10μm were formed by formulating the slurries in which the particles are weakly flocculated by reversible bridging.

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Structural factors controlling tensile deformation of crystalline polyolefins such as polyethylene (PE) and polypropylene (PP) as well as various polyolefin blends were investigated. It was found that the miscibility of the amorphous region of PP with rubbery polyolefin materials strongly affects the mechanical behavior. Furthermore, we introduced a new structural unit, i.e. the lamellar cluster, which is several stacked lamellae bound by some tie molecules to describe the yielding behavior of spherulitic polymers. It was shown that the tie molecules between the adjacent lamellar clusters plays a central role in tensile yielding process.

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Rheological properties of aqueous suspensions and rheometry for viscoelastic measurements over a wide range of frequency were investigated. The raised cosine pulse method for the measurements was improved by using rectangular pulse strain including high-frequency Fourier components. For further extension of the frequency range, a new rheometer was also developed on the basis of the surface loading method. These methods as well as a conventional dynamic method were utilized to determine rheological properties of aqueous solutions of an end-associating polymer (suspending media for resin particles). The relaxation behavior of these solutions was in good agreement with predictions of the Tanaka theory for transient networks. Aqueous suspensions of poly(acryl-co-styrene)(AS) particles with radius a₀=45nm showed linear viscoelastic relaxation behavior, and the time-volume fraction superposition was found to be valid. In the linear regime, AS particles behaved as the Brownian hard particles having an effective radius a_eff = a₀ + ξ with ξ being a thickness of the electric double layer, and the dependence of their zero-shear viscosity η₀ on an effective volume fraction φ_eff (= {a_eff /a₀}³ φ ) agreed with the dependence of η₀ of ideal silica suspensions on the bare volume fraction φ . In the range of φ_eff < φ _m (φ _m ; random close packing volume fraction), η₀ was well described by the Brady theory for Brownian particles. In the range of φ_eff > 0.6, a repulsive force due to overlapping electric double layers also contributed to the viscoelastic behavior of AS suspensions. In aqueous suspensions of polystyrene (PS) particles, flocculation and sedimentation of PS particles occurred on addition of a small amount of the associating polymer. Analysis of the polymer conformation at the particle surface suggested that the polymers formed interparticle bridges thereby inducing of the flocculation and sedimentation.

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A particle simulation method is proposed for computing the dynamics of fiber and platelike particle dispersed systems. In this method, a particle is modeled by using arrays of spheres. Considering the deformation of the particle, each pair of adjacent spheres is connected with three types of springs; stretch, bend, and twist. The motion of the particles in flow is followed by solving the translational and rotational equations of motion for each constituent sphere. The mobility matrix for each particle is calculated to obtain the hydrodynamic force and torque exerted on each sphere. For the hydrodynamic interaction among particles, the near-field lubrication force is considered when the separation between spheres belonging different particles is close, but the far-field part is neglected. The method was applied to predicting the rheological properties of particle dispersed systems and the motion of fillers during an injection molding process of thermoplastics.

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Multi-arm star polystyrenes with various lengths and number of arms were synthesized, and their dynamic viscoelastic properties were investigated in the molten state. The master curves of the storage modulus for the multi-arm stars showed a shoulder at low frequencies, suggesting that a new mechanical relaxation exists at the long time scales after completion of entanglement relaxation. The enhancement of the zero-shear viscosity compared with the regular star polymers was also observed for the multi-arm star polymers.

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Deformation mechanisms under large deformation and spinning rheology of segmented poly(urethane-urea) were studied with the object of achieving ideal rubber elasticity, excellent elastic recovery and dye-affinity. The hysteresis behavior was verified by the fact that the irreversible transverce orientation of the hard segments occurred at low extension due to formation of spherulites structures. Copolymerization of hard segment was shown to improve hysteresis behavior and give rubber-like stress-strain relation. In order to improve elastic recovery at low temperatures, copolymerizing soft segment was found to be effective in preventing crystallization in its fixed state.@The tertiary nitrogen group copolymerized in soft segment had the greatest effect on dye-affinity. Furthermore introducing tertiary nitrogen group into soft segments had the effect on elastic recovery at low temperatures. Spinning stress computed at the take-up point was found to be useful for describing the segmental orientation and the aggregate structure of the hard segment. Adequate spinning conditions were provided by simulation of the dry spinning process in relation to microstructure and orientation.

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