X-ray reflection studies of polymers at interfaces

Using X-ray reflectivity, polymers at interfaces are investigated. The absolute coverage and packing of a fluorosurfactant, $\rm F\sb3C(CF\sb2)\sb7$-$\rm SO\sb2N(C\sb2H\sb5)$-$\rm(CH\sb2CH\sb 2O)\sb74CH3$ is determined. We found the coverage to be 34 A$\sp2$/molecule, with the fluorocarbon segments in contact with vapor phase oriented along the surface normal, and the ethylene oxide segments close-packed underneath. However, there is an ambiguity of the orientation of the ethylene oxide segments undetermined. The equation-of-state of end-grafted poly(p-tert-butylestyrene) is determined by varying solvent (toluene) vapor pressure and controlling the temperature. The results are close to mean-field predictions while self-consistent field theory does not prove to be as good a model in this situation. The deviation between the experimental and theoretical results is due to the overestimation of the entropy of mixing between chain segments and solvent molecules, which may be caused by interference from chain stretching. Water swelling in multilayered polyelectrolyte thin films were studied. The thickness changes of the films may be result of the diffusion of water molecules. A full thermodynamic interpretation of the results is still under investigation. As an experimental technique, the x-ray reflectivity method is first reviewed and discussed