High energy ion irradiation is an emergent process to modify material surface. This irradiation results in implantation of foreign atoms as well as displacement of atoms in material surface layer at low temperatures at which the diffusion of atoms is limited.The ion irradiation often generates a metastable amorphous phase in the surface layer. The ion irradiation also generates high residual compressive stress in the surface layer. The amorphous and compressively stressed layer is demonstrated to be beneficial to improvement of mechanical properties of ceramics. During post-irradiation thermal-annealing, implanted foreign atoms coalesce each other to make metal particles, and react with matrix atoms to make compounds. These are also shown to modify magnetic, optical and other properties of materials.

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Unsteady viscoelastic flow generated by sudden application of a constant flow rate in a circular pipe is experimentally considered. The pressure loss and velocity change with time were measured using 1% aqueous solution of PAA and 1.5% aqueous solution of CMC. For the pressure loss, the inertia effect has been observed just after the startup, and subsequently the overshoot has been found for the 1% aqueous solution of PAA. The overshoot behavior is similar to that for the startup flow under a constant shear rate. In contrast with Newtonian fluids, which exhibit a monotonic development in the velocity change, the 1% aqueous solution of PAA shows the overshoot and oscillation of the centerline velocity before reaching the steady state at a high shear rate. For the 1.5% aqueous solution of CMC which is less elastic than the 1% aqueous solution of PAA, overshoots have been observed both for the pressure loss and the centerline velocity, though the overshoot is weaker than that for the 1% aqueous solution of PAA.

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The longest relaxation time τ_m, of linear polystyrene solutions was studied by stress relaxation after cessation of steady shear flow. The concentration of the solutions are in the region where one can call“semidilute” for zero-shear viscosityη⁰ or “dilute” for steady-state compliance J_e. The time τ_m was compared with the weight-average relaxation time τ_w which was defined as product of η⁰ and J_e. It is concluded that τ_m is proportional to τ_w in this region, as in a well-entangled region. It is also pointed out that the concentration dependence of characteristic time for self-diffusion is similar to that of the relaxation times obtained from viscoelastic measurements.

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Shear and elongational flow properties of high density polyethylene melts are studied. Effects of long branching and molecular weight distribution on rheological properties are investigated for two types of samples, which are produced using different kind of catalysts.
The following conclusions are obtained. (1) Contribution of a relaxation mechanism with very long relaxation times due to the long branch of the sample appears in dynamic viscoelastic functions, relaxation modulus and in elongational viscosity. (2) Difference in shear flow properties between two types of samples is marked in the region corresponding to much lower stress level than that met in the measurement of melt flow rate. (3) The strain dependence of damping function obtained in stress relaxation measurement is similar to each other for two types of samples. (4) Sharp upturn of elongational viscosity is observed for two samples; one with long branch (es) and other with (possibly) extremely high molecular weight tail.

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Dynamic viscoelastic properties and stress relaxation behavior of column-fractionated high density polyethylene melts are studied. Effects of long branching on the rheo-logical properties are investigated for fractions obtained from two types of whole polymers which are produced using different kind of catalysts.
The following conclusions are obtained from the measurements on fraction samples with and without long branches. Fractions including polymer chains with long branches have relaxation mechanism with long relaxation times due to their branched structure. It is found that long branching produces strong effects on viscosity and compliance in the terminal region: Zero-shear viscosity η₀, shows stronger dependence on molecular weight M_w than the usual power-low dependence. Steady state compliance J_e⁰ exhibits unusually strong dependence on molecular weight distribution.This apparent strong-dependence is attributed to the molecular weight dependence of J_e⁰ in the branched samples. From stress relaxation experiments, it is found that effects of long branching and molecular weight distribution on the damping function h(γ) are minor in high density polyethylene melts.

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