Surface dilational moduli of poly(vinyl acetate), poly(methyl methacrylate), and their blend films spread at the air–water interface

Surface dilational moduli of poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), and PVAc/PMMA blend films spread at the air–water interface were investigated as a function of surface concentration. Moreover, the surface dilational moduli of the PVAc/PMMA blend films were measured as a function of the molar fraction of PVAc for the first time. The surface dilational modulus of an expanded PVAc film increased as the surface concentration increased up to 0.75 mg/m2, which corresponded to the limiting surface area of PVAc. After peaking at this value, the surface dilational modulus decreased with increasing PVAc surface concentration. The surface dilational modulus of a condensed PMMA film increased steeply as the surface concentration increased from 1.00 to 1.45 mg/m2. The magnitude of the surface dilational modulus of PMMA was larger than that of PVAc at a fixed surface concentration. This difference was primarily attributed to the fact that PMMA is a condensed polymer whereas PVAc is an expanded polymer. The surface dilational moduli of the incompatible PVAc/PMMA blend films at fixed surface pressures decreased and approached those of PVAc as the molar fraction of PVAc increased, irrespective of the surface pressure. These findings suggest that PVAc components in the blend films are preferentially adsorbed at the air–water interface.