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.

Block copolymer–nanoparticle composites: Structure, functional properties, and processing

“…The effect of heating on thiol-terminated PS-PEO grafted gold NPs (Au-thiol-PS-PEO) inside PSpoly(methyl methacrylate) (PMMA) BCP was studied [85]. Initially, the outer shell of the gold NPs was covered with PEO that was compatible with the PMMA blocks, thus, the particles were Annealing by applying a gradient thermal can be beneficial in aligning NPs and polymeric domains in self-assembled BCP and BCP-NP composite materials, where the thermal gradient can trigger a "soft shear" process [317,318]. For example, annealing of silica NP-containing PS-PMMA BCP composites by applying a gradient thermal field facilitated the formation of highly aligned vertical arrays of NPs [317,318].…”

Orientation Control and Crystallization in a Soft Confined Phase Separated Block Copolymer

“…Several approaches have been used to manipulate the orientation of copolymer microdomains, including electric fields 17,18 , solvent fields [19][20][21][22] , chemically patterned substrates 23 , thermal gradients 24 , shear [25][26][27][28][29] , and AFM tips [30][31][32][33][34][35] .…”

Entropy-driven segregation of polymer-grafted nanoparticles under confinement

“…1). In cases I and II, the smooth surface topography of the blend films were unperturbed, whereas, in case III, capillarity induced rapid mold filling (13,14) and generated patterned topography composed of alternating mesas and trenches with a pitch, λ = (752 ± 6) nm, and a step Significance Functional polymer nanocomposite thin films demand precise control over the spatial organization of nanoparticles on microscales and nanoscales. We demonstrate that conformational chain entropy can be used as a driving force to direct nanoparticle redistribution in blend systems where the enthalpic interactions are negligible.…”