Surface-pressure gradients in monolayers of poly(methyl methacrylate)

Compression of poly(methyl methacrylate) (PMMA) monolayers generates gradients in surface pressure similar to but smaller than those previously reported for monolayers of poly(vinyl stearate) (PVS). The gradient increases sharply with compression of the condensed film and is dependent on the molar mass of the polymer: the higher the molar mass, the steeper the gradient formed. Both the spreading and compression techniques affect, to some extent, the formation of the gradient, but a serious gradient implying inhomogeneity in the monolayer is always produced during compression. When the compression is stopped, the gradient may decay to a limited extent in the first 10 min, but it then remains relatively constant. The collapse pressure of PMMA monolayers suggested by these experiments is 17-20 mN m-1. None of the isotherm measurements for PMMA or PVS monolayers can satisfy the requirements of Huggins' theory on polymer monolayers. Some discrepancies in the published isotherms of PMMA monolayers can now be attributed to the inhomogeneity of the film