Continuous and patterned deposition of functional block copolymer thin films using electrospray
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olymers/Soft Matter Research Letter
Continuous and patterned deposition of functional block copolymer thin films using electrospray Hanqiong Hu and Kristof Toth, Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511, USA Myungwoong Kim, Department of Chemistry, Inha University, Incheon 402-751, Republic of Korea Padma Gopalan, Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin 53706, USA Chinedum O. Osuji, Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511, USA Address all correspondence to Chinedum Osuji at [email protected] (Received 7 February 2015; accepted 26 May 2015)
Abstract We report the use of electrospray to continuously deposit thin films, including patterned films, of a block copolymer (BCP). High substrate temperatures led to vertically oriented cylindrical microdomains at the film surface independent of the solvent composition and deposition rates utilized. Conversely, low substrate temperatures resulted in morphologies that were more sensitive to these parameters, with poorly ordered films of globular structures observed at the lowest temperatures considered. The deposition pattern is defined by spatially varying the electric field at the substrate using an underlying charged grid. These results open up new possibilities for patterned deposition of BCP films with morphological control.
Introduction Block copolymers (BCPs) have been explored extensively as a platform for nanofabrication due to their self-assembly on pertinent length scales (∼5–100 nm), and the versatility of available means for controlling the length scale and chemical functionality through molecular design. Properly leveraging BCP self-assembly in nanotechnology requires the ability to produce well-ordered or potentially defect-free morphologies in the relevant geometry associated with a given application. A variety of directed self-assembly methods have been developed towards these ends, as recently reviewed.[1] In thin films, manipulation of interfacial interactions is often times the salient issue for controlling morphology. In the absence of solvent, a so-called non-preferential or block neutral interface is required to produce perpendicularly oriented lamellae and cylinders by thermal annealing. This has been achieved through substrate modification using random copolymer brushes/mats[2–4] as well as self-assembled monolayers.[5,6] Solvent vapor annealing (SVA), on the other hand, utilizes film swelling and deswelling by volatilized species to accelerate ordering kinetics, manipulate interfacial interaction, and drive alignment. SVA can produce a variety of morphologies which are often kinetically trapped relative to those produced by thermal annealing under the same conditions. Recent advancements in SVA have enabled in-depth understanding of critical factors in dictating film morphology, including the selectivity of solvent, film swelling ratio, and solvent removal rate, due to more precise control
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