Large-Grained Cylindrical Block Copolymer Morphologies by One-Step Room-Temperature Casting

Abstract

We report a facile method of ordering block copolymer (BCP) morphologies in which the conventional two-step casting and annealing steps are replaced by a single-step process where microphase separation and grain coarsening are seamlessly integrated within the casting protocol. This is achieved by slowing down solvent evaporation during casting by introducing a nonvolatile solvent into the BCP casting solution that effectively prolongs the duration of the grain-growth phase. We demonstrate the utility of this solvent evaporation annealing (SEA) method by producing well-ordered large-molecular-weight BCP thin films in a total processing time shorter than 3 min without resorting to any extra laboratory equipment other than a basic casting device, i.e ., spin- or blade-coater. By analyzing the morphologies of the quenched samples, we identify a relatively narrow range of polymer concentration in the wet film, just above the order–disorder concentration, to be critical for obtaining large-grained morphologies. This finding is corroborated by the analysis of the grain-growth kinetics of horizontally oriented cylindrical domains where relatively large growth exponents (1/2) are observed, indicative of a more rapid defect-annihilation mechanism in the concentrated BCP solution than in thermally annealed BCP melts. Furthermore, the analysis of temperature-resolved kinetics data allows us to calculate the Arrhenius activation energy of the grain coarsening in this one-step BCP ordering process.

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

“…74,92 Three notable variations on this theme have produced well-ordered BP thin films: nonvolatile solvent vapor annealing, 92 plasticizer assisted solvent annealing, and solvent evaporation annealing. 74 In contrast to fast evaporation from typical solvents used for film casting (e.g., toluene, ∼1000 nm/s), the drying rates for the nonvolatile solvents vary from <0.1 to ∼4 nm/s. 74 The relatively long drying times for these nonvolatile solvents enable BPs to develop their nanostructure without the need for an enclosure.…”

“…As opposed to reintroducing solvent into a thin film, it also is possible to cast BPs from a mixture of volatile and nonvolatile solvents to slow the evaporation so the thin-film nanostructure can develop (Figure b,c). , Three notable variations on this theme have produced well-ordered BP thin films: nonvolatile solvent vapor annealing, plasticizer assisted solvent annealing, and solvent evaporation annealing . In contrast to fast evaporation from typical solvents used for film casting (e.g., toluene, ∼1000 nm/s), the drying rates for the nonvolatile solvents vary from <0.1 to ∼4 nm/s . The relatively long drying times for these nonvolatile solvents enable BPs to develop their nanostructure without the need for an enclosure.…”

“…74 In contrast to fast evaporation from typical solvents used for film casting (e.g., toluene, ∼1000 nm/s), the drying rates for the nonvolatile solvents vary from <0.1 to ∼4 nm/s. 74 The relatively long drying times for these nonvolatile solvents enable BPs to develop their nanostructure without the need for an enclosure. Furthermore, these methods easily integrate into R2R processing, as they simply require adjusting the casting solution and providing ample time for the nanostructures to develop.…”

Solvent-assisted self-assembly of block copolymer thin films

“…147 Copyright 2019 American Chemical Society, (f-h) adapted with permission from Macromolecules, 53, 11178. 40 Copyright 2020 American Chemical Society.…”

Developing Anisotropy in Self‐Assembled Block Copolymers: Methods, Properties, and Applications

“…Several methodologies introduced in the previous content can be performed on an industrial-scale R2R processing line such as zone annealing and direct immersion annealing. [96,97,369,537,538] Other methods such as raster annealing also show some promises as an inexpensive approach with potentially compatible production rate. [276,539] However, these methods could sometimes suffer from a long processing time for aligning BCP nanostructures (at least hours) since typical workflow of many applications could require multiple processing steps to be finished within minutes.…”