Abstract
Nanoparticles provide an attractive route to modifying polymer thin film properties, yet controlling the dispersion and morphology of functionalized nanoparticle filled films is often difficult. Block copolymers can provide an ideal template for directed assembly of nanoparticles under controlled nanoparticle-polymer interactions. Previously we observed that neat films of cylinder forming poly(styrene-b-methyl methacrylate) PS-b-PMMA block copolymer (c-BCP) orient vertically with dynamic sharp thermal cold zone annealing (CZA-S) over wide range of CZA-S speed (0.1-10) m/s. Here, we introduce a low concentration (1-5 wt %) of nanoparticles of phenolic group functionalized CdS (fCdS-NP), to PMMA cylinder forming polystyrene-b-poly (methyl methacrylate) block copolymer (c-BCP) films. Addition of the fCdS-NP induces a vertical to horizontal orientation transition at low CZA-S speed, V=5 m/s. The orientation flip studies were analyzed using AFM and GISAXS. These results confirm generality of our previously observed orientation transition in c-BCP under low speed CZA-S with other nanoparticles (gold [Au-NP], fulleropyrrolidine [NCPF-NP]) in the same concentration range, but reveal new aspects not previously examined: (1) A novel observation of significant vertical order recovery from 5-10% vertical cylindrical fraction at V=5 m/s to 46-63% vertical cylindrical fraction occurring at high CZA-S speed, V=10 m/s for the fCdS nanoparticle filled films. (2) We rule out the possibility that a nanoparticle wetting layer on the substrate is responsible for the vertical to horizontal flipping transition. (3) We demonstrate that the orientation flipping results can be achieved in a nanoparticle block copolymer system where the nanoparticles are apparently better-dispersed within only one (matrix PS) domain unlike our previous nanoparticle system studied. We consider facile processing conditions to fabricate functionalized nanoparticles filled PS-PMMA block copolymer films with controlled anisotropy, a useful strategy in the design of next generation electronic and photonic materials. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 604-614