There are two contributions to the rms roughness of a polymer-polymer interface; i) the so-called ¿intrinsic interfacial width¿ due to mixing of the polymers at a molecular level and ii) lateral roughness due to deviations of the interface position from the plane of the substrate (due, for example, to thermally excited capillary waves at a liquid-liquid interface). Molecular mixing and lateral roughness at conjugated polymer interfaces will have considerably different effects on polymer device performance, and it is therefore important to distinguish them. Using the high flux/low background capabilities of Inter this proposal seeks to extend our off-specular studies by probing in-plane structures on lengthscales smaller than the typical nematic domain sizes of these polymers (~ 1 micron), which we anticipate may be sgnificantly different to the structure on larger in-plane lengthscales.