Continuous Equilibrated Growth of Ordered Block Copolymer Thin Films by Electrospray Deposition

Abstract

Deposition of block copolymer thin films is most often accomplished in a serial process where material is spin coated onto a substrate and subsequently annealed, either thermally or by solvent vapor, to produce a well-ordered morphology. Here we show that under appropriate conditions, well-ordered block copolymer films may be continuously grown under substrate equilibrated conditions by slow deposition of discrete subattoliter quantities of material using electrospray. We conduct time-resolved observations and investigate the effects of process parameters that underpin film morphology including solvent selectivity, substrate temperature, block-substrate selectivity, and flow rate of the feed solution. For a PEO cylinder-forming poly(styrene-b-ethylene oxide) block copolymer, we uncover a wide temperature window from 90 to 150 °C and an ideal flow rate of 2 μL/min for ordered film deposition from dilute acetone solutions. PEO cylinders aligned with their long axes perpendicular to the film-air interface at optimal spray conditions. Using poly(styrene-b-methyl methacrylate) deposited onto neutrally selective surfaces, we show that the substrate-equilibrated process results in vertically oriented microdomains throughout the film, indicating a preservation of the initial substrate-dictated morphology during the film deposition. Electrospray offers a new and potentially exciting route for controlled, continuous growth of block copolymer thin films and manipulation of their microstructure.

Isoporous Block Copolymer Membranes

“…The alignment of the block copolymer's microdomains is influenced by parameters like the substrates' topo­graphy, its selectivity of interactions towards the different blocks of a block copolymer, the top surface, the liquid treatment of a porous support prior to film casting, or the film thickness, and also epitaxial growth of crystalline domains has been studied . Besides spin‐coating or dip‐coating also spraying or electrospraying of block copolymer solutions on a solid substrate have been demonstrated to yield well‐aligned morphologies in thin films . The application of a carefully controlled temperature protocol during solvent vapor annealing was demonstrated to have a strong influence on the alignment of cylindrical polystyrene‐ block ‐poly(4‐vinylpyridine) diblock copolymers (PS‐ b ‐P4VP), which tend to align parallel to the substrate .…”

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

“…Similar effects were seen with cylinder‐forming PS‐ b ‐PMMA . Other interesting annealing methods that promote vertical microdomains have been reported as well, including zone casting, electrospray deposition, and in situ annealing during spin coating . However, these techniques will not be discussed since the ordering mechanism is based on solvent evaporation, much like solvent vapor annealing.…”

Non‐Native Block Copolymer Thin Film Nanostructures Derived from Iterative Self‐Assembly Processes

“…Pioneering works by Osuji and co‐workers demonstrated how the deposition of BCP layers by electrospray deposition suggests an ability for the formation of complex morphologies, only by selecting the sequence of BCP materials deposition . Indeed, the deposition of sub‐micron droplets formed by electrospray fluid atomization allows the continuous growth of BCP thin films providing a versatile approach to build composite layered BCP nanostructures.…”