CHARACTERIZATION OF MOLECULAR INTERFACES IN HYDROPHOBIC SYSTEMS

Interactions between typical hydrophobic materials, such as hydrocarbo n, fluorinated hydrocarbon and dimethylsiloxane, and water were invest igated by contact angle and sliding angle as experimental methods and together with computational method. Results showed that interactions e nergy of the fluoro-polymers obtained by the experiments amounted to a bout three times higher than that of polydimethylsiloxanes, and it was coincident with the order of that obtained by the molecular orbital m ethod. Generally, for the evaluation of hydrophobic properties, contac t 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 a ngle (theta; 117.0 degrees) than that of polydimethylsiloxanes having a lower one (theta; 95.8 degrees) have been observed. To clarify the r eason of these phenomena, trial calculations for the stabilization ene rgies in the optimization of geometry in the hydrophobic molecular/wat er 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 interac tion energies of FHC/water were very small. From the facts, a few cont act points in this system will be predicted. The distance and bond ang le of water molecules obtained by further calculations predicted the p ossibilities that the value of the contact angle is composed of enthal py and negative excess entropy which structure enhancement of water mo lecules must influence. In consideration of enthalpy and entropy the i nteractions were discussed, and the contradictory phenomena between a and or could be elucidated. (C) 1997 Elsevier Science S.A.