Lamellar block copolymers, with the lamellae standing perpendicular to the substrate, are attractive candidates as templates for nanostructure array fabrication. However, no process currently exists to impose long-range in-plane alignment of such perpendicular lamellae on simple unpatterned substrates - to align the lamellar normal over macroscopic distances. Here, we have generated such aligned films of perpendicular lamellae in a polystyrene- poly(methylmethacrylate) diblock, PS-PMMA, by neutralizing the substrate with a random terpolymer brush and shearing the film with a moving polydimethylsiloxane (PDMS) pad in contact with the film surface. At sufficiently high shear stresses, the lamellae align over the entire (cm2) area of the pad; the perpendicular orientation of the lamellae is preserved, although for films thicker than the lamellar spacing, a "capping layer" of PS forms in contact with the PDMS pad. However, when compared with typical shear-aligned block copolymers having a morphology of in-plane cylinders, a significantly higher stress is required to align the lamellar PS-PMMA, and the orientational order is poorer and the dislocation density higher; a limiting order parameter ψ2 ≈ 0.8 is achieved at high stresses.
ASJC Scopus subject areas
- Condensed Matter Physics