Managing polymer surface structure using surface active block copolymers in block copolymer mixtures

Surface coatings were prepared from semifluorinated monodendron surface-active block copolymers (SABC) and a thermoplastic elastomer (TPE) [poly(styrene-b-ethylene butylene-b-styrene)] by either spin-casting a bilayer structure or by blending. The surface of these coatings was characterized by contact angle measurements, scanning force microscopy (SFM) and near-edge X-ray absorption fine structure (NEXAFS) methods. Both bilayers and blends resulted in very low energy surfaces under the right processing conditions and the liquid crystallinity of the semifluorinated monodendrons gave rise to temporally stable, non-reconstructing surfaces in water. However for small thicknesses of the SABC top layer or for low SABC content blends, SFM shows islands of the fluorinated block of the SABC and incomplete surface coverage of the TPE, an observation confirmed by NEXAFS analysis. Very high water contact angles were produced by even modest amounts of SABC in either case but to achieve low contact angle hysteresis, it was necessary to produce uniform surface coverage by the SABC. Such uniform coverage can be accomplished by spin casting a top layer of SABC as thin as 60 nm in the bilayer case but at least 10 wt% SABC in TPE combined with drop casting of a hot solutions is needed for the blends to achieve equivalent surface structure and properties.