Simultaneous In-Film Polymer Synthesis and Self-Assembly for Hierarchical Nanopatterns Zhe Qiang, Sahil A. Akolawala, and Muzhou Wang* Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208, United States * S Supporting Information ABSTRACT: A key requirement for practical applications of nanostructured block copolymer (BCP) self-assembly is the ability to generate complex geometries including different shapes and diverse sizes across one substrate surface. This has been difficult because spatial control over the underlying chemistry of the BCP has been limited. Here, we demonstrate a photocontrolled in-f ilm polymerization process in the presence of monomer vapor for synthesizing homopolymers in self-assembled BCP films. The homopolymers blend with BCPs and alter the nanopatterns by changing the underlying polymer chemistry and composition. We apply this technique to a variety of BCPs including polystyrene-b-polyisoprene-b-polystyrene, polystyrene-b-poly(methyl methacrylate), and polystyrene-b-poly(4-vinylpyridine). The region of in-film polymerization can be modulated by the location of irradiation using photomasks for obtaining distinct morphologies on one substrate, providing a new platform for hierarchically manipulating nanopatterns within the self-assembled BCP thin film as well as opening up a new area for radical polymerizations of monomers within such geometrically confined, swollen films. B ottom-up patterning of polymers has attracted significant interest due to its advantages of low cost and spontaneous nanoscale order. 1,2 As an example, directed self-assembly (DSA) of block copolymers (BCPs) has emerged as a next- generation lithographic technique to generate well-defined nanodomains uniformly across the large areas. 3-6 Many applications such as electronic circuits or magnetic storage media require versatile patterns with di fferent regions containing different features on one substrate. 7,8 Previous reports for generating hierarchical BCP nanopatterns have relied on patterned substrates or photolithography combined with kinetic trapping of a nonequilibrium morphology, 9-11 controlling interfacial surface energy, 12 or adjusting interaction parameters (χ) between different blocks. 13,14 However, these methods are limited to only altering the orientation or ordering degree of the nanodomains since the morphology of each region is ultimately controlled by the chemistry of its underlying BCP. Alternatively, complex nanostructures can be fabricated from block copolymer blends 15,16 or by depositing different BCPs on different regions in multiple steps, with cross-linking and etching steps in between. 17-19 However, these approaches become more challenging with increasing complexity of the desired final patterns as one BCP only corresponds to one fixed size and morphology. 20 The constraints on these strategies indicate a limited control of the polymer chemistry within defined locations on a polymer film. True on-demand synthesis in polymer films integrated with self-assembly would enable exact hierarchical control over the resulting morphology, functionality, and properties. Here, we demonstrate an in-f ilm photocontrolled free radical polymerization process for in situ polymer synthesis within a block copolymer thin film swollen with monomer vapor. The synthesized homopolymers blend with the self-assembled BCP films, which modify the morphology and domain spacing by altering the chemistry and composition. By providing sufficient mobility within the film for polymerization and nanostructural rearrangement, this method integrates polymer synthesis with simultaneous BCP self-assembly, providing a new route for on- demand nanopattern manipulation. This method also enables hierarchical control over the resulting morphology and functionality through local irradiation of films. Our in-film polymerization method adapts and combines photoinitiated radical polymerization with common solvent vapor annealing processes for simultaneously synthesizing homopolymers and ordering BCP thin films. The process involves three steps as illustrated in Figure 1a: 21 (1) A polymerizable monomer is introduced from the vapor phase into an optically transparent chamber to swell a photoinitiator- embedded BCP film. (2) With constant monomer vapor feeding through mass flow controllers, the swollen film is irradiated with ultraviolet light, causing the photoinitiator to generate free radicals that initiate polymerization of the monomers. (3) The reaction is terminated when the radical species are completely consumed or irradiation is removed. Followed by removal of UV, the films are dried by replacing monomer vapor with pure N 2 . The reaction produces homopolymers through a photocontrolled process within the Received: February 14, 2018 Accepted: April 16, 2018 Letter pubs.acs.org/macroletters Cite This: ACS Macro Lett. 2018, 7, 566-571 © XXXX American Chemical Society 566 DOI: 10.1021/acsmacrolett.8b00119 ACS Macro Lett. 2018, 7, 566-571