Structure and permeability of composite films of two analogous acrylate methacrylate copolymers.

Two analogous acrylate methacrylate copolymers, A and B, which form films with compact surface zones (skins) have been layered into composite films AB and BA. Electron micrographs of the composite film internal structure revealed a porous asymmetry; the mean pore size in layer A was 2.4 +/- 0.3 microns, and that in layer B 0.71 +/- 0.06 microns. The actual surface pores were considerably smaller than the internal pores, below the limit of resolution of the electron microscope. AB (layer A accepting the permeant first) was 17 times more permeable to the solute, urea, than BA. Exposure of the film surfaces to solvent vapor before layering caused dissolution of the "skin" in component layers; resulting composite films were therefore more permeable than theoretical expectation.