Reduced domain size and interfacial width in fast ordering nanofilled block copolymer films by direct immersion annealing

Block copolymers (BCPs) can function as nanoscale templates to organize nanoparticles within selective domains. Most functional applications of nanofilled BCPs generally require a high loading of nanoparticles, which is difficult to achieve due to particle aggregation, slow kinetics of ordering, and disruption of block copolymer order. A key parameter is the periodic domain spacing, L₀, which is important for tuning functional properties. We demonstrate direct immersion annealing (DIA) as a promising directed self-assembly (DSA) method to overcome these problems. DIA is shown to fully order highly filled (10.5 vol % Au-PSrPMMA nanoparticles) lamellar poly(styrene-b-methyl methacrylate) (PS-PMMA) BCP films, whose lamellar ordering is practically unimpeded by filler loading. Neutron reflection (NR) further confirms that DIA sharpens the interfacial width between PS-PMMA domains by ∼20%. In situ NR studies further reveal that DIA predominantly induced film ordering in a 5 wt % anisotropic organoclay (C93A) filled PS-PMMA film in less than 30 s! In contrast, identical C93A nanofilled PS-PMMA films that were thermally annealed (19 h at 160 °C) only exhibit partial ordering near the free surface. DIA films also exhibit ∼50% reduced L₀, resulting in twice the number of BCP domains, potentially useful to film functional properties such as gas barrier when filled with clay or plasmonics for gold nanoparticles. We further model this reduced L₀ in DIA processed films with a scaling approach to correlate the final structure to degree of polymerization, N. Our results reveal that DIA, a roll-to-roll (R2R) compatible DSA method, can enable real-time manufacture of nanofilled block copolymers for functional applications.