Templated Self-assembly of PS-<i>branch</i>-PDMS Janus Bottle Brush Copolymer

Self-assembly of block copolymers is a promising route for technological applications to fabricate numerous structures with length scales of a few to several hundred nm. However, scalability below 10 nm remains challenging. Here we show that novel Janus-type bottle brush copolymers (BBCPs) break conventional χN limit, scaling with the length of the side chains instead of the overall backbone length. We report the synthesis and self-assembly of PS-branch-PDMS BBCP, featuring a backbone with a tunable degree of polymerization connecting immiscible blocks, instead of having each type of sidechain at one end of the molecule as in conventional BBCPs. Thin morphologies of BBCP with f_PDMS = 26% and M_n = 609 kg/mol were investigated using solvent vapor annealing. Long-range ordered 22-nm cylindrical microdomains in thin films were achieved, and the correlation length was quantified under different as-cast film thickness, solvent vapor pressure, and composition of the binary mixture of solvent vapors. Rapid dynamic self-assembly process was characterized using In-situ GISAXS. Templated self-assembly of BBCP within lithographically patterned substrate was demonstrated, showing distinct pattern orientation and dimensions that are difficult to achieve from traditional block copolymers.