Architectural effect of polymer nanoparticles on block copolymer ordering

Much of the focus on block copolymer/nanoparticle (BCP/NP) nanocomposites has been on the passive dispersion of NPs inside the BCP matrix. However, recent studies have looked into the active role of NPs in controlling the orientation of BCP thin film microdomains by an entropy-induced segregation of the NPs to the substrate and/or free surface. Notwithstanding the recent progress in understanding such systems, these nanocomposite systems are not yet fully understood because of the complex mechanism that arises when these two moieties meet. In this work, we employed organic nanoparticles (ONPs) in the form of star polymers and single chain nanoparticles (SCNPs) are used as fillers in 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 ∼30, 21, and 6 arms and SCNPs are used as fillers in PS-b-PMMA thin films in an attempt to produce perpendicular microdomains. Consequently, it was observed that ∼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. The versatility of this method is evidenced by its applicability to both cylinder and lamellae systems.