Study of the Compatibility of Polymer Chains in the Two Dimensions

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We have studied the structures and compatibility of binary mixed polymer chains spread at the air/water interface using the techniques of surface pressure measurements and ellipsometry. We chose four different polymers such as poly (ethylene oxide)(PEO), poly (methyl acrylate) (PMA), poly (vinyl acetate) (PVAc), and poly (methyl methacrylate) (P-MMA). All polymers lead to a stable film spread at the air-water interface.1. From the plots of the experimental mean area of the mixed polymer films at a constant surface pressure as a function of the mole fraction of one component in the films, PEO/PMMA mixtures and PMA/PVAc mixtures are compatible in their entire composition. For PVAc/PEO mixtures, they are compatible below the collapse surface pressure of PEO. In PVAc/PMMA mixtures, the mixtures are thermodynamically unstable and should not be compatible. These results correlate well with the compatibility of the corresponding mixtures in the bulk state.2. Ellipsometry showed that the thickness of the PEO/PMMA mixture layer adsorbed on the air-water interface at the high surface concentration does not exceed 2.5 nm, independent of composition in the mixtures. This thin layer thickness seems to be governed by the flat conformation of the individual film for PEO and PMMA. On the other hand, the thickness of the adsorbed layer for the PMA/PVA mixtures gives an increase with the surface concentration and reaches a plateau value. The plateau thickness attains to 15nm and its value is almost the same as the pure PVAc thickness.