β-cyclodextrin and its hyperbranched polymers-induced micro/nanopatterns and tunable wettability on polymer surfaces

Abstract

This paper reports an efficient strategy to fabricate micro/nanopatterns on the surfaces of polymers for obtaining tunable wettability. Tepee-like bundles as micro/nanopatterns, composed of irregular polygon “podium” and “valley” structures, are formed by adding β-cyclodextrin (β-CD) or its hyperbranched polymers [HBP(β-CD)s] into a polystyrene (PS) matrix in the process of anodized aluminum oxide (AAO) template wetting. The degree and region of micro/nanopatterns are evidently enlarged with the increase of β-CD content or the molecular weight (M_w) of HBP(β-CD). The formation of micro/nanopatterns is mainly dependant on the self-organization of long and flexible aligned nanofiber/nanotube arrays with high aspect ratios, which are generated by the enhanced nanoflow behaviors of β-CD or HBP(β-CD)-containing PS melts in AAO templates. The final topographies of micro/nanopatterns are determined by the dilation stress and the interactions of nanofibers/nanotubes during the template's removal and solvent evaporation process. The static and dynamic water contact angle measurements show that the wettability of micro/nanopatterned surfaces is systematically tuned from being merely hydrophobic to being highly hydrophobic, and to being finally superhydrophobic by simply adjusting the content of β-CD or the M_w of HBP(β-CD) due to the decrease of the contact area fraction of the water droplet and solid polymer. The reported novel method, using nanoparticles or hyperbranched polymers as processing aids to induce micro/nanopatterns and tunable wettability on polymer surfaces, may be extended to various polymeric matrices to realize nanopatterns, and is useful for tailoring artificial superhydrophobic surfaces as well.