Film thickness controllable wet-imprinting of nanoscale channels made of conducting or thermoresponsive polymers

Abstract

We report the fabrication of structured polymer films via a novel imprinting routine, which additionally allows for entire surface coverage by an underlying homogeneous polymer film. The imprinting method is based on an inverted micromolding in capillaries (MIMIC) approach and in combination with master molds made of bisphenol-A–polycarbonate (PC) sample sizes of up to 20 × 30 mm² were perfectly structured. Nanoscopic channel structures made of the conducting poly(3,4-ethylenedioxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS) and the thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) also prove the wide application possibilities of this structuring method. For PEDOT:PSS structures the film thickness of the homogeneous supporting polymer layer can be controlled between 0 and 80 nm by an externally applied pressure during imprinting. In addition, conducting polymer blend films as they are used for organic solar cells have a reduced optical reflection if spin cast onto such structured PEDOT:PSS films. For channel structures made of PNIPAM it is shown that their macroscopic optical grating effect responds to the environmental humidity. Due to water inclusion in the PNIPAM network unifying of adjacent channels occurs already in the early stages of the swelling process and results in a homogeneous polymer film. Finally a first batch processing device for the structuring routine is demonstrated, which also guarantees constant lift-off conditions.