Determination of order in polysiloxane Langmuir-Blodgett films using the overlayer Patterson function

For the analysis of ultrathin layer systems with partial order, we demonstr ate a navel Patterson-function analysis of the small-angle X-ray scattering which does not rely on any detailed or unphysical assumptions about film s tructure and order. The one-dimensional overlayer Patterson function of the film is shown to present the information from the measurements in real spa ce in an intuitively accessible form and to be more appropriate for partial ly ordered systems than the box models in common use. We apply the analysis to determine the structure of multilayer Langmuir-Blodgett films of a numb er of sidechain-substituted polysiloxane derivatives. We demonstrate that i t allows conclusions to be drawn about the asymptotic decay of layer order correlations and the detailed distribution of electron density within the b ilayer repeat unit, both of which are inaccessible to box-model methods.