THE SURFACE-TENSION OF POLYMER BLENDS - THEORY AND EXPERIMENT

The surface tensions of a series of miscible polymer blends were measured using a modified Wilhelmy method. The results were compared with the Cahn-Hilliard theory where the Flory, Orwoll, and Vrij equation of state was used to model the bulk properties of the blends. Experimental results for blends of low and high molecular weight (MW) poly(dimethylsiloxane) (PDMS) were found to agree with theory to within experimental error with no adjustable parameters. The results indicate that we can accurately model the surface excess of the low molecular weight PDMS component. The theoretical dependence of the surface tension of the blend on the square gradient coefficient kappa12 is also described. Blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) were also studied. Both theory and experiment indicated that there is a strong surface excess of PVME. The PS-PVME system is known to have an attractive specific interaction which gives rise to miscibility. This attractive potential was included in the theory via an interaction parameter, to give quantitative agreement between theory and experiment. The magnitude of the interaction term is consistent with that used for modeling the phase behavior of this system.