Highly hydrophobic flip-flop-type ultrathin coating films prepared via electrostatic self-assembly

A flip-flop-type hydrophobic coating film consisting of oppositely charged poly(allylamine hydrochloride) (PAH) and a perfluorosulfonate ionomer (Nation) ultrathin layers was prepared via layer-by-layer (LbL) assembly. The thickness of a Nafion layer was estimated to be 6.7 nm from the amount of deposited Nafion. The PAH/Nafion multilayers are optically transparent in UV-Vis region from 300 to 800 nm, and extremely small amount of Nafion was used for the coating (approximately 1.1 microg/cm2). The contact angle for water droplet of the PAH/Nafion multilayers was approximately 105 degrees. On the other hand, the contact angle for water droplet decreased rapidly from 105 degrees to approximately 85 degrees after being kept in closed vessel (approximately 100% of relative humidity) for 90 min. (approximatley 100% of relative humidity) for 15 h. The PAH/Nafion multilayer again showed hydrophobicity with the contact angle of 102 degrees after being dried at 125 degrees C for 30 min. PAH/Nafion multilayers obtained are hydrophobic in air and hydrophilic in water, namely flip-flop-type amphiphilic coating films.