Akinori Fujinami

Adsorption process of Zn2O2 on a crystal polyimide surface

Energetics of the adsorption process of a Zn2O2 cluster on a crystal polyimide surface were investigated using an atomistic approach combining a semi-empirical molecular orbital method and algorithms that can find the optimal path of a chemical reaction process. We demonstrated that chemical reactions occur between the Zn2O2 cluster and the crystal polyimide surface and that the reactions always involve chemical bonding between a Zn atom of the cluster and a carbonyl oxygen atom in the polyimide.

Yield behaviour of rubber-modified epoxy adhesives under multiaxial stress conditions : Effect of plastic deformability of the matrix phase

In a previous study, the yield stress in the adhesive layer of scarf and torsional butt joints with a rubber-modified adhesive was measured, and the results agreed with those calculated by a finite element method, where Gursons constitutive equations were applied to the adhesive layer. In this study, to investigate the effect of plastic deformability of the matrix phase on the yielding behaviour of rubber-modified epoxy adhesives, the yield behaviour was investigated by using scarf and torsional butt joints, where a reactive diluent was used to vary the plastic deformability of the matrix phase. The applicability of Gursons model was examined in terms of the yield stresses calculated by a finite element method with a variety of the model parameters. As a result, it is confirmed that the yield stresses of the rubber-modified adhesives with different matrix phases can be approximately estimated by Gursons model, and the model parameters agreement with the experimental data increases with increasing the plastic deformability of the matrix phase.

Molecular Orbital Study on Adsorption Process of Silica Cluster on Polyimide Surface

Process of a silica cluster on a polyimide surface was simulated by atomistic calculations combining the semi-empirical molecular orbital method and algorithms that can find the optimal path of a chemical bonding process. Specifically, we estimated the activation and sorption energies in the process. From the simulations, we found that chemical bonding occurs between a silica cluster and the polyimide substrate surface. In the adsorption processes, those reactions between the silica cluster and the polyimide surface which involve Si-O bonding between the cluster and the polyimide are the most probable.

Molecular Orbital Study on Interfacial Strength between Oxide Cluster and Polyimide Substrate

Adsorption processes between silica cluster and poly-(p-phenylene pyromellitimide) substrate are investigated by the atomistic calculations combining with the semi-empirical molecular orbital method and the algorisms that can find minimum energy paths of chemical bonding process. Especially, the activation and sorption energies in the reactions are estimated from the optimal reaction path. The Silica thin film-aromatic Polyimide substrate interface is modeled by a silica cluster and polyimide surface which is layered molecular chains with periodic boundary conditions. Conjugate gradient and Quick-Min methods are used to determine atomistic configurations of the system at local minimum and to evaluate physisorption energy. The dimer and the nudged elastic band (NEB) methods, which use only first derivatives of the potential energy, are used in order to search minimum energy paths on the potential energy landscape. The dimer method is started from local minimum on the potential energy landscape and used to search the transition and final states of the system. The NEB method is then carried out to calculate precise path by using final state obtained by the dimer method. From the simulations, we find that the chemical bonding occurs between a silica cluster and polyimide substrate surface, and the sorption energy defined by the sum of physisorption and chemisorption energy are evaluated. Moreover, we discuss the interfacial strength of silica-polyimide substrate using the optimal minimum energy paths.

Damage Behavior of Adhesive Butt Joints Bonded with Rubber-Modified Epoxy.

In the present study, damage behavior in the adhesive layer of adhesive butt joints bonded with rubber-modified epoxy was investigated by using an anisotropic damage theory. In the experiments, the stress-strain curves of the bulk specimens and the adhesive layer in the butt joints were measured by loading-unloading tests at a relatively low strain rate. The values of damage parameter D1 in the maximum principal stress direction were obtained from the measured stress-strain curves for the specimens. The relation between D1 and the strain energy density given to the specimens was investigated in order to compare the damage behavior of the butt joint and bulk specimens. From the results, it was found that the strain energy density of the specimens given until they break increased with rubber contents, but their damage behaviors were almost the same. It was also found that the strain energy densities of the specimens at their fracture were almost the same but the damage parameter D1 of the butt joint specimen was higher than that of the bulk specimen over the full range of strain energy.