The mean-field intermolecular interaction contribution in interfacial statistical associating fluid theory (iSAFT) is extended to include correlation functions, which could be evaluated from molecular simulation and the density functional theory (DFT) itself. Order-disorder transitions (ODTs) between lamellar and disordered phases for pure block copolymers and copolymer nanoparticle composites are reported, and the extended theory has been shown to give good agreement with molecular simulations and considerable improvement over the previous mean-field dispersion description. The interaction parameters at ODT are also correlated with the length of copolymers. Concentration profiles of different species are then calculated and compared quantitatively with simulation. The scaled microstructures predicted by the theory agree with simulation for all the nanoparticle size and surface chemistry investigated. Improvements over previous DFT reports have also been observed for large selective nanoparticles. iSAFT has been shown to be capable of modeling BCP from different segregation regimes using a single framework and predicting characteristic exponent for chain length dependence of lamellar spacing, in good agreement with other theories in all segregation regimes.