PARTIAL STRUCTURE FACTOR-ANALYSIS OF NEUTRON REFLECTOMETRY FROM SPREAD MONOLAYERS OF ISOTACTIC POLYMETHYL METHACRYLATE

Neutron reflectivity data for isotactic polymethyl methacrylate monolayers spread at the air-water interface have been analysed using the kinematic approximation. For surface concentrations up to 1.0 mg m-2 the data are well modelled by a uniform layer of thickness circa 20 angstrom. Water may be uniformly dispersed throughout the film. However to obtain agreement with the experimental reflectivities, a proportion of air must be included in the film which agrees with the findings of an earlier optical matrix type analysis. For surface concentration above 1 mg m-2, the uniform layer model does not reproduce the surface concentrations and the data is better fitted by a layer with a Gaussian distribution of segments in the aqueous phase. The benefits of the kinematic approximation are that an insight into the organisation of polymers at the air-water interface can be obtained rapidly without the need for detailed fitting procedures inherent in the use of optical matrix methods.