Toshio Fujibayashi

Characterization of molecular interfaces in hydrophobic systems

Abstract Interactions between typical hydrophobic materials, such as hydrocarbon, fluorinated hydrocarbon and dimethylsiloxane, and water were investigated by contact angle and sliding angle as experimental methods and together with computational method. Results showed that interactions energy of the fluoro-polymers obtained by the experiments amounted to about three times higher than that of polydimethylsiloxanes, and it was coincident with the order of that obtained by the molecular orbital method. Generally, for the evaluation of hydrophobic properties, contact angle measurements are up to the present prevailing. Experimentally, however, antagonistic results, in which a water droplet hardly slides down on the surface of fluorinated polymers having a higher contact angle (θ; 117.0 °) than that of polydimethylsiloxanes having a lower one (θ; 95.8 °) have been observed. To clarify the reason of these phenomena, trial calculations for the stabilization energies in the optimization of geometry in the hydrophobic molecular/water systems using crystallized models of water, when its segment brings on the surface of water, were made. Bond angles, distances of O H···O of two water molecules were calculated. Results showed that interaction energies of FHC/water were very small. From the facts, a few contact points in this system will be predicted. The distance and bond angle of water molecules obtained by further calculations predicted the possibilities that the value of the contact angle is composed of enthalpy and negative excess entropy which structure enhancement of water molecules must influence. In consideration of enthalpy and entropy the interactions were discussed, and the contradictory phenomena between θ and α could be elucidated.

A novel binder suitable for cationic electrodeposition coatings based on a non-isocyanate chemistry

Abstract A non-polyisocyanate resin system that can be applied to cationic electrodeposition (CED) paint has been developed. Most of the compositions of binders currently on the market as CED coatings are composed of modified epoxy resins and blocked polyisocyanates, their crosslinking essentially being polyurethane or polyurea formation. This report deals with a new resin system of which crosslinking is based on a ring-opening/etherification reaction between epoxy groups and hydroxyl groups. The ring-opening addition reaction has very low emissions during the baking process. However, it is difficult to attain a compromise between satisfactory reactivity at elevated temperatures and stability in aqueous composition. By a series of careful investigations, we have established the composition of CED coatings that are sufficiently stable and can be satisfactorily cured. The CED paint formulated on this resin system has such desirable properties as low weight loss upon baking, outstanding weatherability, and excellent chipping resistance. Other characteristics are comparable to existing polyisocyanate based CED coatings.