Log-Rolling Block Copolymer Cylinders

Shear is an effective method to create long-range order in micro- or nanostructured soft materials. When simple shear flow is applied, particles or polymer microdomains tend to align in the shear direction to minimize viscous dissipation; thus, transverse alignment (so-called log-rolling) is not typically favored. This is the first study to report the transverse alignment of cylinder-forming coil-coil block copolymers. Poly(styrene-b-methyl methacrylate), PS-PMMA, where the PS blocks form the matrix, can adopt a metastable PMMA hemicylindrical structure when confined in a thin film, and this hemicylindrical structure can orient either along the shear direction or transverse to the shear direction depending on the shearing temperature. A monolayer of PS-PMMA forming full cylinders exhibits log-rolling alignment. This unusual log-rolling behavior is explained by the low chain mobility of the cylinder-forming PMMA block at low temperatures, which is the critical quantity determining the direction of shear alignment.