nano-texturing research group

Substrate adhesion was investigated experimentally for superhydrophobic coatings fabricated from polyurethane modified with waterborne perfluoroalkyl methacrylic copolymer and a (fatty amine/amino-silane surface modified) montmorillonite clay nanofiller. The superhydrophobic coatings were obtained by spray casting precursor solutions onto aluminum surfaces. Upon thermosetting, initial static water contact angles exceeding 160° and contact angle hysteresis values below 8° were measured, yielding antiwetting and self-cleaning characteristics. Adhesion strength was then characterized with a 90° tape testing method and was analyzed with respect to changes in surface morphology via electron microscopy as well as changes in wettability. The coating remained adhered to the substrate after repeated adhesion testing with 3850 N/m tape (one of the strongest available), showing higher adhesion than any superhydrophobic coating reported to the author’s knowledge. Superhydrophobic performance was also shown to be retained even after repeated tape testing.

This work investigates temperature and humidity effects on the superhydrophobicity of polyurethane/organoclay nanocomposites. Previous reports of superhydrophobic degradation at decreasing surface temperatures for both low and high humidity were generally conducted in open environments. However, the present setup allows a thermally homogeneous environment, i.e., the temperature of the nanocomposite, air and water droplet are equal with no spatial temperature gradients. In such conditions, results showed stable retention of superhydrophobicity for both low humidity (RH < 20%) cool-down and warm-up cycles (20 °C to −3 °C to 20 °C). Similar performance was also observed for a high humidity (RH > 80%) cool-down cycle, though superhydrophobicity degraded during the warm-up cycle, which was attributed to dew condensation.

Nano-structured polyurethane/organoclay composite films were fabricated by dispersing moisture-curable polyurethanes and fatty amine/amino-silane surface modified montmorillonite clay (organoclay) in cyclomethicone-in-water emulsions. Cyclomethicone Pickering emulsions were made by emulsifying Decamethylcyclopentasiloxane (D5), Dodecamethylcyclohexasiloxane (D6) and aminofuctional siloxane polymers with water using montmorillonite particles as emulsion stabilizers. Polyurethane and organoclay dispersed emulsions were spray coated on aluminum surfaces. Upon thermosetting, water repellent self-cleaning coatings were obtained with measured static water contact angles exceeding 155o and low contact angle hysteresis (<8o). Electron microscopy images of the coating surfaces revealed formation of self-similar hierarchical micro-and nano-scale surface structures. The surface morphology and the coating adhesion strength to aluminum substrates were found to be sensitive to the relative amounts of dispersed polyurethane and organoclay in the emulsions. The degree of superhydrophobicity was analyzed using static water contact angles as well as contact angle hysteresis measurements. Due to biocompatibility of cyclomethicones and polyurethane, developed coatings can be considered for specific bio-medical applications.

A conformal coating process is presented to transform surfaces with inherent micro-morphology into superhydrophobic surfaces with hierarchical surface structure using wet chemical spray casting. Nanocomposite coatings composed of zinc oxide nanoparticles and organosilane quaternary nitrogen compound are dispersed in solution for application. The coating is applied to a micro-patterned polydimethylsiloxane substrate with a regular array of cylindrical microposts as well as a surface with random microstructure for the purpose of demonstrating improved non-wettability and a superhydrophobic state for water droplets. Coating surface morphology is investigated with an environmental scanning electron microscope and surface wettability performance is characterized by static and dynamic contact angle measurements. 

The authors report fabrication of tough nanostructured self-cleaning superhydrophobic polymer-organoclay films from anaerobic acrylic adhesives displaying strong adhesion to metal surfaces. Both industrial and bio-grade anaerobic adhesives such as bone cements could be used. Montmorillonite clay filled anaerobic adhesives were modified by blending with a water dispersed fluoro-methacrylic latex in solution to form abrasion resistant interpenetrating polymer network films upon spray casting. The adhesive films could cure by thermosetting in oxygen-rich environments. Very high contact angles with low hysteresis were also measured for acidic (pH 2) and basic (pH 11) aqueous buffer solutions indicating resistance to acidic and basic media.