Masuo Kudo

Dynamic viscoelastic properties and thermal properties of Ni powder–epoxy resin composites

The composite materials containing metal Ni powder of 5–15 μm in size were prepared by use of the matrix epoxy resin of glycidyl amine crosslinked with bis-4-amino-3-methylcyclohexyl methane and 2,4-diamine 3,5-dimethyltoluene. Dynamic viscoelastic properties of the composites at various volume fraction (Φp) of Ni powder have been measured over the temperature range from 30 to 300°C. The peak temperatures in dynamic loss modulus–temperature diagrams of the composite increased with increasing Φp, although the peak position was abruptly shifted to lower temperatures in the range of Φp more than 0.245. At this high concentration of Φp, agglomeration of the particles occurring in the composite lead to reduction of the interaction between Ni particle and epoxy resin. Parallel studies on the thermal conductivity (λ) of the composites materials showed that the value of λ at Φp = 0.245 increased by approximately 7 times that of the original epoxy resin. The shape of Ni particles also affected the thermal durabilities of the composites; the rough surface of Ni powder yields a higher storage modulus of the composite than that of the materials containing the powder with a smooth surface, which had been brought through a ball-milling process. The finding suggested that the increasing in specific surface area of the powder improved the thermal durability of the composites as well as their mechanical properties.

Piezoelectric Poly-L-Lactic Acid Film Prepared by a New Method

The possibility has been indicated that polymers with helical chirality, such as poly-L-lactic acid (PLLA), show a large optical rotatory power ρ (about 9600 deg/mm: J. Kobayashi et al., J. Appl. Phys. 77 (1995) 2957) or piezoelectric constant in their fiber axial direction (helical chain direction). To attempt the realization of a new optical or piezoelectric active polymer device, we fabricated the PLLA on a basal plate using end-grafted polymer technology. The structure of PLLA on a basal plate was observed by atomic force microscopy. As a result, we found that the PLLA on a basal plate with annealing grows into have a needle-like structure. The roughness of the aggregate PLLA on a basal plate is 12.5 nm. ρ of the PLLA on a basal plate is about 80 deg/mm. This ρ value is larger than that of the quartz crystal which is a very well-known crystal with high optical activity. We speculated, on the basis of Kobayashi et al.s report, that the helical chain direction of the PLLA on a basal plate obtained in this study is not perpendicular to but has a fixed angle to the surface of the basal plate.

Rheological properties of magnetic paints containing barium‐ferrite fine particles with various aspect ratios

Static flow properties of magnetic paints containing hexagonal shaped barium‐ferrite fine particles have been investigated in terms of their diameter/thickness aspect ratio. The Ba‐ferrite paints showed typical pseudoplastic flow behaviors with different yield stresses. The flow curves were divided into three types of flow components using Kuin equation as follows: (1) yield stress part, (2) Newtonian flow part, (3) viscoelastic deformation of flocs with stress relaxation. Each flow curve for the Ba‐ferrite paint could be well‐fitted to the theoretical trace by the Kuin equation, and four kinds of rheological parameters were obtained from those procedures. We found that such parameters except for the Newtonian viscosity increase with increasing particle aspect ratio or particle specific surface area. This implies that the rheological properties of Ba‐ferrite paints are strongly governed by the particle interaction forces associated with particle characteristics.