ELLIPSOMETRIC STUDY OF MIXTURE FILMS OF POLY(METHYL ACRYLATE) AND POLY(VINYL ACETATE) AT THE AIR-WATER-INTERFACE

Binary mixed films of poly(methyl acrylate) (PMA) and poly(vinyl acetate) (PVAc) and the individual polymer films at the air/water interface have been investigated by surface pressure measurements and ellipsometry. Both films of PMA and PVAc showed surface pressure-area (pi-A) isotherms of the expanded type film type. However, the limiting area for PMA was smaller than that of PVAc and the collapse surface pressure for PVAc was higher than that for PMA. These results were in agreement with those of Crisp. On the other hand, ellipsometry showed there was no difference between PMA and PVAc films. For the mixed films of PMA and PVAc, the thicknesses and the refractive indices depended on the mixture ratio at the same total surface concentration due to repulsive forces between PMA and PVAc. An increase in PMA in the mixture induced an increase of the thickness as well as a decrease in the refractive index of the mixed films. Immiscibility of PMA and PVAc was confirmed by further experiments on films prepared by using a separate addition of the individual polymers. Therefore, it is concluded that PMA and PVAc mixtures were incompatible at the air/water interface.