Rheological behavior was examined for aqueous suspensions of a mixture of monodisperse polystyrene (S) particles having different radii, 42 nm and 103 nm. The bare volume fraction of the particles, φ, was almost identical in all suspensions examined (φ = 0.42−0.43), and the mixing ratio of the small particles, w_s, was varied. The particles had an electrostatic shell due to the surface charges, and the shell thickness was different for the small and large particles in respective unimodal suspensions. Thus, the viscoelastically effective volume fraction φ_eff (including the shell volume) of the particles, being larger than φ, changed with w_s. In the linear viscoelastic regime, the suspensions exhibited terminal relaxation attributable to Brownian motion of the particles, and the terminal relaxation time τ and zero-shear viscosity η₀ first decreased and then increased with increasing w_s. These viscoelastic features were compared with predictions of the Shikata-Niwa-Morishima (SNM) model considering the Brownian motion of hypothetical unimodal particles with a radius being equal to an average of the radii of the large and small particles. The w_s dependence of τ and η₀ of the aqueous S suspensions was well described by this model, given that the change of φ_eff with w_s was accounted. Under steady flow, the suspensions of the S particles exhibited shear thinning of the viscosity. This thinning, attributable to nonlinearity of the Brownian stress, was less significant for the bimodal suspensions (in particular for the suspension with w _s = 0.25) than for the unimodal suspensions (w_s = 0 and 1). This difference resulted from a difference of the strain γ_col required for particle collision under flow: γ_col was the largest for the bimodal suspension with w_s = 0.25 thereby inducing the weakest thinning in this suspension. In fact, the unimodal and bimodal suspensions exhibited an universal relationship between the normalized viscosity and normalized strain γ / γ_col (with γ being the strain effectively imposed through the flow) irrespective of the w_s value.

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Effects of alkaline metal salts on zero-shear viscosity (η₀) of gellan aqueous solutions were investigated. The temperature (T) dependence curves of η₀ showed a steep change due to the coil-helix transition of the gellan molecules. The transition temperature (T_Tr) depended on the salt concentration while it was independent of the cationic species. At temperatures higher than T_Tr, η₀ decreased with increasing salt concentration. At temperatures lower than T_Tr, T-η₀ curves at various salt concentrations produced a kind of envelope corresponding to the T-η₀ curve for gellan with double-helical conformation. The addition of alkaline salts enhanced the aggregate formation at temperatures lower than T_Tr, and the efficiency for the aggregate formation depended on the cationic species used. At a fixed salt concentration, the degree of aggregation increased in the order of Cs ^{+>Rb+>K+>Na +} >Li. Defining the temperature at which the double helices start to aggregate as T_a, both T_Tr and T_a were not affected by the type of halogens, Cl ^{−, Br− and I−}.

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The rheological properties of pulp and PET fiber suspensions were measured with a parallel-plates type rheometer. A high speed CCD camera was used to observe the changes in the floc structures that were produced during the rheological measurement. The flow curves of the pulp fiber suspensions showed Newtonian flow in the low shear rate range. With increasing shear rate, the shear stress increased and then became unstable, namely, jumps in the flow curves were observed, which are due to the formation of fiber flocs. At a higher shear rate, the flocs disappeared and the systems showed Newtonian flow again. The flow curves of the polyethylene terephthalate (PET) fiber suspensions showed non-Newtonian flow even in the low shear rate range. We found that the uniform distribution of fibers became uneven and then the flocs began to form at the critical shear rate; and over the critical shear rate, the fibers began to uniformly disperse again, i.e., the flocs disappeared. The two-dimensional fast Fourier transform (FFT) technique and Guinier approximation were used to obtain the radius of gyration, R_g, of the flocs. It is considered that the R_g of the flocs is useful to characterize the mechanism of fiber flocculation.

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The steady flow and the dynamic viscoelastic properties of cellulose fiber suspensions were investigated as functions of the suspension concentration and the fiber shape using a parallel-plate type rheometer. Various concentrations of the suspensions were made from various types of cellulose fibers, i.e., microcrystalline cellulose, bacterial cellulose, and fibrillated cellulose fibers. All the suspensions showed non-Newtonian flow even at very low concentrations. The flow property of each suspension showed a plateau of the shear stress, i.e., the yield stress, over a critical concentration. The critical concentration obtained from the experiment agreed well with the value theoretically calculated from the axial ratio of the fibers. The dynamic moduli of the suspensions were almost independent of the angular frequency, and they increased with the fiber concentration. The dynamic storage moduli increased in proportion to the 9/4th power of the fiber concentration. This power of 9/4 is coincident with that theoretically required for polymer gels. This fact suggests that the rigidity of the suspensions has appeared by the same mechanism from the order of cellulose fibers to microcrystalline cellulose fibers, and even to polymer molecules.

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Dynamic viscoelastic properties, steady shear and biaxial extensional flow behaviors have been investigated for melts of potassium titanate whisker filled polyoxymethylene. A second plateau appears in the low frequency region of the storage modulus G', and the plateau value increases with whisker content. Addition of the whisker also increases the steady shear viscosity and the low strain rate asymptote of the biaxial extensional viscosity. The upturn of biaxial extensional viscosity from the low strain rate asymptote decreases by the addition of whisker due to suppression of polymer chain extension. Change in whisker dispersion and orientation in the melts was observed with scanning electron microscopy after quenching the samples in biaxial extensional flow. The degree of whisker orientation to the flow direction decreases with increasing strain rate in the range where the strain rate is much greater than the rate of whisker orientation and it is smaller than or comparable with the relaxation rate of the matrix chain. It is suggested that the matrix does not have enough power to orient the whisker in this range of strain rate.

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Flow-induced phase separation behavior of poly (α-methylstyrenes) in a θ solvent, n-undecyl anisitate and the related viscoelastic properties were studied by rheological and light scattering measurements. The critical shear rate for flow-induced phase separation was consistently determined from integrated intensity of light scattering under the flow and its change after the cessation of flow, as well as from time dependency of dynamic modulus measured after the cessation of flow. It was observed that first normal stress difference and excess shear stress are proportional to shear rate at the shear rate region higher than the critical ones for phase separation. These results are qualitatively consistent with the theories of Onuki (Phys. Rev. A, 35, 5149 (1987)) and Doi and Ohta (J. Chem. Phys., 95, 1242 (1991)). The relative magnitude of excess stresses can be explained if we assume existence of domain structure elongated in the flow direction. At the higher shear rate end of measurement, it was observed that the stresses become not stable and show tendency to diverse. Together with direct observation results of the sample under the flow, it was speculated that the flow-induced gelation occurred at such high shear rates.

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We observed collision and coalescence after application of large step shear strains for two polyisobutylene (PIB) droplets in polydimethylsiloxane (PDMS) matrix using a stereo microscope. When coalescence occurred, interface vanished in an overlapped area of deformed droplets. Then a single droplet recovered to spherical shape. Time necessary for recovery to spherical shape with coalescence was longer than that without coalescence. Coalescence was easy to occur for larger strain and smaller d₀/r ₀, where d₀ and r₀ represent initial distance between centers of droplets and initial droplet radius, respectively. In the case of shape recovery without coalescence, the distance between the centers after shape recovery was smaller than d₀. Time dependence of shape of droplets was similar in both cases with coalescence and without coalescence. Ratio of length of overlap, l_ov', to length of semi major axis, a', in view perpendicular to shear plane determines occurrence of coalescence.

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A new graph-theoretical method for calculating the dynamical properties of Rouse-Ham chains with any branches is presented. The characteristic polynomial for its line graph, which has the bonds of a molecular graph as its beads with adjacency of bonds as in the graph, makes it possible to provide us with the relaxation spectrum of any tree-like chain.

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Branched nylon12 was prepared by polycondensation of 12-aminododecanoic acid with iminodidodecanoic acid as a branching agent. Dynamic viscoelasticity, step large deformation and uniaxial extensional flow behaviors in melt and creep behaviors in solid for branched and linear nylon12 were measured. The creep behaviors under high load for branched nylon12 were superior to those for linear nylon12.

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Nonlinear relaxation modulus G(t, γ) was examined for two types of ABS polymers, the ABS-T(1) system containing agglomerated network of rubber particles and the ABS-T(3) system in which the rubber particles were randomly dispersed. Both systems exhibited fast and slow relaxation processes, the former reflecting the relaxation of the SAN chains and the latter being attributed to motion of the network and/or dispersed rubber particles. The relaxation modulus of the chains, G_chain(t,γ), was evaluated by subtracting the modulus for the slow process from the G(t,γ) data. This G_chain(t,γ) exhibited the time-strain separable damping, and its longest relaxation time τ_g-SAN was attributed to the entanglement relaxation of the SAN chains grafted on the rubber particles. For the ABS-T(1) system, τ_g-SAN rapidly increased with the volume fraction of the gel components φ_gel (@ volume fraction of the particles) for small φ_gel (< 0.2) and then leveled off at larger φ_gel (≥ 0.2). This behavior was related to rapid increase and saturation of the entanglement density for the grafted SAN chains on full development of the tightly connected network occurring at small φ_gel. In contrast, the τ_g-SAN of the ABS-T(3) system increased gradually with φ_gel, reflecting gradual increase of the entanglement density for the SAN chains grafted on the randomly dispersed rubber particles. Thus, the difference in the dispersion state of the rubber particles in the ABS-T(1) and ABS-T(3) systems naturally resulted in the difference in the entanglement relaxation time of the grafted SAN chains.

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The first and second normal stress differences, N ₁ and N₂ in steady shear flow are calculated using differential constitutive equations proposed by Leonov and Giesekus. At low shear rates, the Leonov model gives -N₂/ N₁=0.25 for both single and multiple relaxation modes. In the Giesekus model, −N₂/ N₁ increases with increasing anisotropy mobility parameter α. Both models predict that −N₂/N₁ is a decreasing function of the shear rate at high shear rates. The shear rate dependence of −N₂/N₁ becomes weaker with increasing width of relaxation time distribution. The BKZ type integral constitutive equation is employed to investigate the effect of a model parameter b (=N₂/N ₁) on steady planar, uniaxial and biaxial extensional flows. It is found that the strain rate dependences of planar2 and biaxial extensional viscosities are very sensitive to the parameter b, where 2 in planar extension denotes the direction of constant width.

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