Brownian dynamics (BD) simulations of the steady and transient rheological behaviors of FENE dumbbell model for dilute polymer solutions in uniaxial extensional flow are reported. The simulations include examination of the effects of distributions of maximum allowable extension (FENE parameter b) and of relaxation time parameter α. Stretch-thickening and strain-hardening behaviors, which can be often observed in polymer solutions, are confirmed in the simulations either with or without the distribution of b or α. However, overshoot phenomenon in a start-up extensional flow can never be observed unlike the situation in a start-up shear flow. Curves of transient extensional viscosity vs. strain clearly show that the extensional viscosity is independent of the stretch rate in the regime of αλ₀ε>1~2 where polymer solutions exhibit significant strain-hardening. Furthermore, it is found that the distribution of b has little influence on extensional flow properties while the distribution of α can affect both the steady and transient extensional flow properties under the distribution condition used in the simulations. BD simulation can precisely predict the extensional viscosity even in the low stretch rate region.

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The dependence of physical aging kinetics on glass-forming histories and thermal treatments was examined for amorphous poly (ethylene terephthalate) (PET) glasses. The samples were subjected to two-step thermal treatment : first, temperature drop from equilibrium at 80°C to 60°C and then isothermal annealing ; second, temperature jump to aging temperature T_a. Isothermal volume recovery was measured after the second step to T_a (70°C> T_a>60°C) below the glass transition temperature (T). The volume recovery curves were represented by a plot of normalized fractional free volume (=(V-V_∞)/V_∞, where V_∞ is the equilibrium value of specific volume V) vs. logarithm of aging time. All curves, showing the well known “memory effect” characteristic, could be described nearly by a six-parameter phenomenological model postulating a multiplicity of independent relaxation modes with distinct relaxation times. The model parameters determined to fit the data were found to be greatly dependent on the glass-forming history, but weakly dependent on the thermal treatment conditions. Furthermore, the individual recovery curves could be superimposed by horizontal shifts along the logarithm axis of aging time.

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A contribution of the crosslinks changed in character by aging in oil-extended SBR vulcanizates to the stress-strain relation was examined with the following theoretical constitutive equation : f={G-B(1-1/α)+C(α²-1)+D(α+1/α²-2)+f(α⁴-1}(α-1/α²) where f is nominal stress at an extension ratio α, G corresponds to rigidity, B, C, D, and F are coefficients. The experimental stress-strain relations of oil-extended SBR vulcanizates aged for various periods of time at 100°C coincided with the above relation in the extension range almost up to the break. The dependence of each coefficient on the crosslink densities was examined and found that a part of the crosslink density in aged oil-extended SBR was effective on the stress. The rate of the effective crosslink densities for each coefficient was determined for each period of aging time. On the basis of the effective crosslink densities, a method estimating the stress-strain curves of aged oil-extended SBR vulcanizate was proposed.

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New procedure to couple glass beads with epoxy resin has been proposed. Bisphenol A type of epoxy resin (E828) cured with ethylenediamine (EDA) is reinforced by glass beads (GB's). GB's surface treated by silane coupling agents (SA) are mixed with E828 at 100°C~180°C before the curing agent EDA is added, in order to increase the reaction between the SA and E828. As a result, the glass transition temperature, flexural modulus and strength of composites mixed at 150°C have exhibited the highest values, respectively. Moreover, the scanning electron microscopy observation of the fractured surfaces of composites has shown that the method of mixing at 150°C is effective to improve the GB / E828 interfacial adhesion.

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We improved the imbedded fiber retraction (IFR) method as a simple method to obtain the interfacial tension between polymer melts. A force balance equation for a fiber in an immiscible matrix by Cohen and Carriere is solved for a more realistic fiber shape at later stage of retraction. Moreover, unknown hydrodynamic coefficient in the balance equation is determined theoretically as 0.125. The interfacial tension between polystyrene (PS) and poly (methy methacrylate) (PMMA) is measured by the improved IFR (IIFR) method as well as the breaking thread method and dynamic viscoelasticity method. In dynamic viscoelasticity method, we determine the interfacial tension by fitting the Palierne theory with dynamic viscoelastic data. The interfacial tension obtained from the three methods agrees fairly well and is found to be about 1.6 mNm^-1 at 180°C and 1.4mNm^-1 at 200°C.

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Viscoelastic liquid behaves like elastic solid at frequencies higher than its relaxation times. The storage modulus, G'(ω), becomes independent of the angular frequency, ω, and the loss modulus, G"(ω), becomes much smaller than G'(ω). On the other hand, the behavior of the first normal stress difference, N₁(ω), is quite different from that of elastic solid. In particular, it is always non-zero in contrast with that for solid. We examine the origin of difference based on the concepts of permanent and temporary networks of polymer chain. It is shown that the difference is detected only with experiments of long duration, longer than the maximum relaxation time of the system.

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For a wide variety of systems, structures under flow have been investigated with rheo-optical techniques. It is of particular interest and importance to examine the flow effects on structures and dynamics with different techniques. A rheo-dielectric technique, that detects dynamic dielectric responses under flow, is complementary to rheo-optical techniques and provides us with a very useful method of investigating these effects. This article gives a brief review of rheo-dielectric features of some model systems revealed in recent studies to demonstrate the applicability of the rheo-dielectric technique.

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