Daniel Sweat, Samantha Schmitt, Myungwoong Kim, Xiang Yu, Padma Gopalan
The chemistry of the dual functional coating which has an embedded initiator for growth of polymer brushes, and functions as a non-preferential layer for the assembly of a overlying block copolymer (BCP) film is shown on the left side. The right side of the figure shows the process of removal of the minority domain, exposure of the embedded initiator, the growth of polymer brushes in the confined cylinders, and the removal of the BCP template to create high density nanopatterned brushes on the substrate.
Thrust 1 research has demonstrated an organic thin-film with dual functionality; namely the ability to both control BCP domain orientation in thin-film and then use the overlying template for the growth of dense array of nanopatterned polymer brushes with high fidelity. A coating consisting of a lightly crosslinked thin film made from a random copolymer consisting of an Atom Transfer Radical Polymerization (ATRP) inimer, styrene and glycidyl methacrylate (GMA) was developed. The amount of inimer was held constant at 20 or 30% while the relative amount of styrene to GMA was varied to tune the neutrality and achieve vertical domain orientation in an overlying P(S-b-MMA) block copolymer (BCP) film for lamellar and cylindrical morphologies.
A cylinder forming BCP blend with PMMA homopolymer was assembled to create a vertical array of hexagonal cylinders which allowed access to a nanoporous template under mild conditions. Surface-initiated ATRP of 2-hydroxyethyl methacrylate was conducted through the pores to generate a dense array of nanopatterned brushes. Alternatively, gold was deposited into the nanopores, the template removed and brushes were grown around the dots. This is the first example of combining the chemistry of neutral surfaces with surface initiated growth of polymer chains. While the chemical contrast in these patterned brushes can be tailored to create a chemical pattern for any block copolymer assembly, the implications of this methodology extends into areas such as chemically defined biointerfaces.