Toshikatsu Manabe

Interaction between polymers and magnetic particles: effect on the properties of particulate magnetic recording media

The interaction between vinyl chloride–vinyl acetate-vinyl alcohol copolymers and cobalt-modified γ-Fe2O3(Co–γ-Fe2O3) magnetic particles has been studied. Adsorption isotherms and heats of adsorption were measured for polymers with various kinds and concentrations of functional groups. The interaction of the polymer with Co–γ-Fe2O3, and the amount of polymer adsorbed, increased in proportion to the hydroxy-group concentration of the polymer. Introducing a few carboxy groups into the polymer also produced stronger interaction. This interaction affected the properties of particulate magnetic recording media considerably. The interaction strength of the polymer with Co–γ-Fe2O3 has been shown to determine the Youngs modulus of a magnetic coating layer. Stronger interaction led to higher dispersibility of Co–γ-Fe2O3 in the magnetic coating layer.

The surface chemical properties of cobalt-modified γ-Fe2-O3 magnetic particles

The surface chemical properties of cobalt-modified γ-Fe2O3 (Co-γ-Fe2O3) magnetic particles were studied by adsorption isotherms, FT-i.r. spectroscopy and microcalorimetry. The monolayer-adsorption amount of water on Co-γ-Fe2O3 surfaces is 4.8 molecules per square nanometre, and the surface is considered to be covered with a thin water film in its normal environment. The surface hydrophilicity of Co-γ-Fe2O3 is comparable to that of TiO2. The acidic carboxyl group shows the strongest interaction with Co-γ-Fe2O3, and a portion of this group chemically interacts. The basic amino group indicates stronger interaction with Co-γ-Fe2O3 than the neutral hydroxyl group. It is concluded that the Co-γ-Fe2O3 surface possesses a basic rather than an acidic character. This is interpreted in terms of the inherent nature of the adsorption site of Co-γ-Fe2O3. Furthermore, the Co-γ-Fe2O3 adsorption site appears to be energetically heterogeneous.