title: Dynamic thermal field-induced gradient soft-shear for highly oriented block copolymer thin films.
abstract: As demand for smaller, more powerful, and energy-efficient devices continues, conventional patterning technologies are pushing up against fundamental limits. Block copolymers (BCPs) are considered prime candidates for a potential solution via directed self-assembly of nanostructures. We introduce here a facile directed self-assembly method to rapidly fabricate unidirectionally aligned BCP nanopatterns at large scale, on rigid or flexible template-free substrates via a thermally induced dynamic gradient soft-shear field. A localized differential thermal expansion at the interface between a BCP film and a confining polydimethylsiloxane (PDMS) layer due to a dynamic thermal field imposes the gradient soft-shear field. PDMS undergoes directional expansion (along the annealing direction) in the heating zone and contracts back in the cooling zone, thus setting up a single cycle of oscillatory shear (maximum lateral shear stress ∼12 × 10(4) Pa) in the system. We successfully apply this process to create unidirectional alignment of BCP thin films over a wide range of thicknesses (nm to μm) and processing speeds (μm/s to mm/s) using both a flat and patterned PDMS layer. Grazing incidence small-angle X-ray scattering measurements show absolutely no sign of isotropic population and reveal ≥99% aligned orientational order with an angular spread Δθ(fwhm) ≤ 5° (full width at half-maximum). This method may pave the way to practical industrial use of hierarchically patterned BCP nanostructures.
authors.affiliation: Department of Polymer Engineering, The University of Akron, Akron, Ohio 44325, United States.
authors.forename: Gurpreet
authors.initials: G
authors.lastname: Singh
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Yager
authors.forename: Brian
authors.initials: B
authors.lastname: Berry
authors.forename: Ho-Cheol
authors.initials: HC
authors.lastname: Kim
authors.forename: Alamgir
authors.initials: A
authors.lastname: Karim
mesh_terms: D003460:Crystallization / Q000379:methods*; D004129:Dimethylpolysiloxanes / Q000138:chemical synthesis*; D006244:Hardness; D008422:Materials Testing; D008567:Membranes, Artificial; D009757:Nylons / Q000138:chemical synthesis*; D033081:Shear Strength; D013696:Temperature; D013814:Thermal Conductivity
chemical_list: D004129:Dimethylpolysiloxanes; D008567:Membranes, Artificial; D009757:Nylons; C085707:poly(dimethylsiloxane)-polyamide copolymer