The elucidation of the compositional profile of polymer:small molecule nanoparticle films is critical for applications such as water processable organic solar cells. In order to have efficient charge separation and transfer, a nanoscale morphology is needed. This is crucial as charge migration only occurs on length scales up to 10 nm, and if separation is larger than this charge recombination occurs, which has a substantial negative effect on overall solar cell performance. Therefore, it is important to see how the morphology of the nanoparticle films change post thermal annealing. Ideally the nanoparticles would melt after heating and maintain their blended interpenetrating nanoscale structure, however the polymer could migrate and form large domains which would hinder device performance. NR measurements would be able to confirm which blend films have optimal internal morphologies.