Organic nanoparticles (ONPs) in the form of star polymers and single chain nanoparticles (SCNPs) are used as fillers in block copolymer (BCP)/ONP nanocomposite thin films to induce perpendicular microdomains without any substrate treatment. The nonselective ONPs for both blocks of BCP neutralize the substrate and the free surface via an entropy-driven boundary surface segregation process, which differs markedly from the conventional neutralization process relying on surface chemistry. To examine the architectural effect of ONPs for surface segregation, neutral star polymers with similar to 30, 21, and 6 arms and single-chain nanoparticles (SCNPs) are used as fillers in PS-b-PMMA thin films in an attempt to produce perpendicular microdomains. Consequently, it was observed that similar to 30- and 21-arm star polymers and SCNPs, which may behave like hard particles having excluded volume interactions with host BCPs, effectively induced perpendicular microdomains, while soft particle-like 6-arm stars led to morphological compatibilization with BCPs.