A study of the supramolecular approach in controlling diblock copolymer nanopatterning and nanoporosity on surfaces

Thin films of poly(styrene-b-4-vinylpyridine) (PS4VP) [Mn(PS) = 71.9 kg/mol; Mn(P4VP) = 30.2 kg/mol] mixed with 1,5-dihydroxynaphthalene (DHN) were dip-coated onto flat substrates from THF solutions. The resultant nanostructures were characterized by AFM, TEM, infrared spectroscopy, contact angle measurements, and cyclic voltammetry. The DHN selectively enriches the P4VP domains through hydrogen bond complexation, giving relative block compositions that should result in lamellar morphology in the bulk. However, films dip-coated from solutions of variable DHN:4VP molar ratios self-assemble into a quasi-hexagonal array of nodules of P4VP + DHN protruding above a PS matrix. This morphology can be ascribed, at least in part, to greater solubility in THF of PS compared to P4VP. The solubility difference appears to be highest for equimolar DHN:4VP. The removal of DHN from the deposited films by rinsing with methanol creates regularly patterned nanoporous films. The geometric parameters of the nanopatterns before and after DHN removal depend on the DHN:4VP ratio. Electrochemical measurements indicate that the pores penetrate the methanol-rinsed films most deeply for those prepared using an initial DHN:4VP molar ratio of 4:1. It was estimated from these measurements that a P4VP layer of about 2 nm thick is located at the film-substrate interface, through which electron tunneling can occur.