The distinctive structures and dynamics of interfacial polymer layer in polymer nanocomposites (PNCs) compared to polymers in bulk phase are responsible for enhancing physical properties of PNCs. Therefore, numerous studies have been dedicated to understanding physical properties of interfacial layer and how these can be affected by size/shape/compositions of particles/polymers in PNCs, usually in the equilibrium state. However, PNCs may remain in the non-equilibrium state as polymers can be kinetically trapped by their slow dynamics during the complex and multiple processing. In this study, we found that the thicker/thinner interfacial layers are formed when the poor/good casting solvent is used despite the same final composition of PNCs. The thickness of the interfacial layer, only differed by a few nm influences greatly the resulting microstructures and properties of PNCs. Importantly, such casting solvent effect is promoted with decreasing particle size.