Directional Self‐Assembly of Fluorinated Star Block Polymer Thin Films Using Mixed Solvent Vapor Annealing

Abstract

We demonstrate the directional alignment of perpendicular‐lamellae domains in fluorinated three‐armed star block polymer (BP) thin films using solvent vapor annealing with shear stress. The control of orientation and alignment was accomplished without any substrate surface modification. Additionally, three‐armed star poly(methyl methacrylate‐block‐styrene) [PMMA‐PS] and poly(octafluoropentyl methacrylate‐block‐styrene) were compared to their linear analogues to examine the impact of fluorine content and star architecture on self‐assembled BP feature sizes and interdomain density profiles. X‐ray reflectometry results indicated that the star BP molecular architecture increased the effective polymer segregation strength and could possibly facilitate reduced polymer domain spacings, which are useful in next‐generation nanolithographic applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1663–1672

From Lab to Fab: Enabling Enhanced Control of Block Polymer Thin-Film Nanostructures

“…For instance, the Epps group demonstrated that solvent vapor annealing with soft shear could be used to produce long-range order for star block polymers with large Flory−Huggins interaction parameters, but achieving the desired nanostructure required carefully chosen solvent mixtures. 41 Another challenge relates to the large parameter spaces involved in block polymer self-assembly. Methods to form a target morphology are impacted by a number of factors, including block chemistry, substrate choice, film deposition method, and film thickness.…”

“…Additionally, equipment can operate as fast as 15 m/s, and nanofabrication techniques that can reach this speed could be transformative. , Furthermore, new and existing approaches need to be demonstrated with application-relevant systems; the effectiveness of these methods cannot be assumed for all polymers, especially because macromolecular characteristics of the systems (e.g., ultrahigh molecular weight or large Flory–Huggins interaction parameters) can impact critical considerations like ordering kinetics. For instance, the Epps group demonstrated that solvent vapor annealing with soft shear could be used to produce long-range order for star block polymers with large Flory–Huggins interaction parameters, but achieving the desired nanostructure required carefully chosen solvent mixtures …”

“…Polymer thin films are typically coated from a dilute polymer solution, and the choice of casting solvent can significantly impact the initial (and final) nanoscale morphology . After a film is cast, the reintroduction of solvent can plasticize the polymer to enable further coarsening of the self-assembled structure and manipulation of the BP phase behaviorthe nanostructure is sensitive to many factors, such as solvent/block compatibility, swelling ratio, and solvent removal rate. , For example, mixtures of solvents can be used to anneal polymers to target a desired morphology on the basis of selective swelling of a block. − Yet, the mechanisms of nanostructure reorganization in these systems need to be understood to improve annealing processes.…”

“…Although magnetic fields can effectively orient certain systems, shear alignment also has been a promising approach because it has both been adapted to work with a number of annealing techniques and tested on many polymer systems. ,,, Typically, an elastomeric pad is placed on top of the BP thin film to transfer shear force that can be produced by two primary mechanisms: lateral displacement or expansion/contraction. ,,,, In general, the former employs heat and a weight on top of the elastomer that is displaced laterally, − and the latter involves solvent swelling/deswelling or heating/cooling to induce expansion and contraction of the pad. ,, To probe the relationship between shear strength and orientation quality for poly­(styrene- b - n -hexyl methacrylate) thin films, Davis et al used an experimental setup that applied a shear gradient as opposed to a single shear stress (Figure a) . Polydimethylsiloxane (PDMS) oil replaced the cross-linked elastomer, and a parallel plate rheometer produced shear stress gradients as a function of radial distance from the center of the film .…”

“…Although magnetic fields can effectively orient certain systems, shear alignment also has been a promising approach because it has both been adapted to work with a number of annealing techniques and tested on many polymer systems. 22,41,61,62 Typically, an elastomeric pad is placed on top of the BP thin film to transfer shear force that can be produced by two primary mechanisms: lateral displacement or expansion/contraction. 51,52,54,55,63 In general, the former employs heat and a weight on top of the elastomer that is displaced laterally, 54−56 and the latter involves solvent swelling/deswelling or heating/cooling to induce expansion and contraction of the pad.…”