Numerous studies have shown that the glass transition temperature, T-g, of polymers may change visibly upon addition of even small amounts of nanoparticles. In this study, we examine the effect of polymer-nanoparticle interfacial energy on this phenomenon in nanocomposite films containing polystyrene-grafted nanoparticles mixed with polystyrene homopolymer at low particle loadings. A previous experiment showed that the interfacial energy of this system modulates with the grafting density of the grafted polymer and the molecular weight ratio of the matrix and grafted polymers. We find that the changes in T-g vary with both parameters in manners that quantitatively agree with the interfacial energy.