Neutron reflection high molecular weight polymers

The time dependence of the early stages of polymer interdiffusion at interfaces is indicative of the diffusion process. The normal approach to study such interdiffusion by neutron reflectivity is to use an anneal/quench cycle where the sample is heated for a given time above the glass transition temperature (Tg) of the polymer, then quenched rapidly to room temperature, after which the reflectivity profile is measured. This has proved to be highly effective for a number of systems, but is difficult to apply when Tg is room temperature, or for small molecule ingress into a higher molecular weight polymer layer. 

If we take typical values of x and substitute into equations (4.3.11) and (4.3.12) we will typically find that we would expect the interfacial width to be a few tens of angstrom imits wide and the interfacial tension a few mJm . Experimental results are relatively sparse these rather low values of interfacial tension are very difficult to measure in polymer melts with their very high viscosities even for relatively modest molecular weights. Interfacial widths of these thicknesses are only practicably measurable by neutron reflectivity. 

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