Depth-influenced structure through permeating polymer membrane using SAXS synchrotron method

Depth-dependent structure of the PU membrane under working conditions performed on a model sample representing a membrane section in the scale 10:1 has been studied. The X-ray scattering in a polyurethane sample, covered by deposited aluminium on both sides, was measured along the sample depth using the synchrotron SAXS beamline. The model sample was saturated with benzene at its bottom, while from its top the solvent evaporated freely. Assuming the lamellar structure of the polyurethane we found that the average inter-lamellar distance increases monotonically from the value measured for the dry polymer to the value obtained for the saturated one. The relation of our result with the existing models of permeation is discussed. Further analysis of the lamellae structure indicated that the increase of the inter-lamellar distance refers only to its amorphous, a less dense part. Furthermore, we found that the change of the inter-lamellar distance is due to gradual formation of the solvent-sensible structure.