MIXED MONOLAYERS OF POLY(VINYL STEARATE) WITH ITS MONOMER

A marked gradient in surface pressure develops in monolayers of poly(v inyl stearate) (PVS) during compression. The gradient varies with posi tion along the trough: it is large in the region close to the compress ion barrier and also near the other end of the trough, but relatively small at intermediate positions. In mixed monolayers of PVS with vinyl stearate (VS) the gradient is large and almost independent of the com position until the VS content exceeds about one third. Further increas es in the proportion of VS cause decreases in gradient, and at VS mole fractions greater than about 0.65 the gradient is negligible. With pu re PVS monolayers the gradient, once formed, remains constant for at l east 90 min, but in films containing VS the gradient slowly decreases. The mixed films exhibit negative deviations in the area per repeat un it when compared to the averaged areas, with the maximum deviation occ urring at a composition of 50 mol% (calculated on the basis of the PVS repeat unit). The fracture pressure is a function of the composition of the monolayer, with the maximum at about 90 mol% of PVS.