Yoshihisa Fujii

Relaxation Behavior of Poly(methyl methacrylate) at a Water Interface

The relaxation behavior of poly(methyl methacrylate) (PMMA), spin-coated on a silicon wafer, at the water interface was examined by lateral force microscopy as a function of temperature and scanning rate. Even in water, the lateral force peak which was assigned to the segmental motion of PMMA plasticized by water molecules was clearly observed in the temperature domain. The apparent activation energy for the plasticized alpha(a)-relaxation process was much smaller than those for the original alpha(a)-relaxation processes at the intact surface and in the bulk. The depth profile of the glass transition temperature (T(g)) of the PMMA film in water was obtained, showing that T(g) decreases with proximity to the water phase. The T(g) depression observed here was best explained in terms of the water content of the film, rather than a confinement effect.

Interfacial Width in Polymer Bilayer Films Prepared by Double-Spin-Coating and Flotation Methods

A spin-coating method with the aid of selective solvents has been used to construct multilayer structures for organic devices under the assumption that the solvents do not invade a preformed structure. To confirm the assumption, we examined the interfacial width (lambda(i)) of model polymer bilayers, composed of polystyrene and perdeuterated poly(methyl methacrylate), prepared by spin-coating and flotation methods. Neutron reflectivity measurements revealed that the lambda(i) value was larger for the spin-coating method than for the flotation method. These results cast doubt on the validity of the assumption. This knowledge should be kept in mind when this method is applied to construct multilayer structures.

One-pot surface modification of rubbery polymer films

A novel method to modify the surface of rubbery polymer films on the basis of the preferential segregation of inorganic materials fed into the system in tiny amounts is proposed. The surface so prepared had several prominent properties such as surface hardness, anti-oxidant properties, transparency, and so forth.

Mobility Gradient of Polystyrene in Films Supported on Solid Substrates

In this review, we show the distribution of glass transition temperature (Tg) in monodisperse polystyrene (PS) films coated on silicon oxide layers along the direction normal to the surface. Scanning force microscopy with a lateral force mode revealed that surface Tg (T s ) was lower than the corresponding bulk Tg (T b g ). Interestingly, the glass transition dynamics at the surface was better expressed by an Arrhenius equation than by a Vogel-Fulcher-Tamman equation. Interdiffusion experiments for PS bilayers at various temperatures, above T s g and below T b g , enabled us to gain direct access to the mobility gradient in the surface region. Tg at the solid substrate was examined by fluorescence lifetime measurements using evanescent wave excitation. The interfacial Tg was higher than the corresponding T b g. The extent of the elevation was a function of the distance from the substrate and the interfacial energy. The Tg both at the surface and interface was also studied by the coarse-grained molecular dynamics simulation. The results were in good accor- dance with the experimental results. Finally, dynamic mechanical analysis for PS in thin and ultrathin films was made. The relaxation time for the segmental motion became broader towards the faster and slower sides, due probably to the surface and interfacial mobility.

Structural analysis for a poly(methyl methacrylate) ultrathin film in water by neutron reflectivity

Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film spin-coated on a substrate in water (H2O) and deuterated water (D2O) were examined along the direction normal to the interface by specular neutron reflectivity (NR). Although H2O and D2O were typical non-solvents for dPMMA, their interfaces were more diffuse than the air/dPMMA interface due to the swelling caused by the sorption of H2O and D2O molecules. An isotopic effect on aggregation structure of the dPMMA film in water was also discussed.