Surface pressure gradients formed during the compression of poly(vinyl stearate) monolayers

Surface pressures have been measured at various positions along the center line of the trough during the compression of monolayers of vinyl stearate (VS) and poly(vinyl stearate) (PVS). With VS there was no appreciable inhomogeneity, but with PVS a significant surface pressure gradient formed. This exhibited an approximately linear decrease in surface pressure from the moving barrier to the end of the trough. The inhomogeneity of the PVS monolayers during compression depends on the technique of spreading and on the method of compression. No technique was found which would eliminate the surface pressure gradient. Even when the film was held at a high surface pressure for 90 min, there was still a significant surface pressure gradient. Much of the earlier data on PVS monolayers, particularly the apparent annealing effect, can be explained by the present findings.