Stimuli-responsive coating by simple physical blending route

Abstract

The article describes a very simple design philosophy of a coating that responds to temperature-rise by changing its behavior from hydrophilic to superhydrophobic in an instantaneous reversible manner. The material developed can be applied to a variety of surfaces simply by brush or roller, making it highly suitable as the basic ingredient of smart paint. Low surface energy fluoro and amino monomers were introduced to prepare the polymer backbone, which was then used as a binder for achieving a nano-micro dual particle morphology based on nano-silica micro-Titania (pre-functionalized with hydrophobic siloxane) by simple physical blending. The final structure was inspired by the so-called lotus effect. The best designed resulting material shows a water contact angle of 152° with a roll off-angle as low as 2° as a coating in response to elevated temperature, changing its hydrophilic nature. This reversible switching is ascribed to the formation and breaking of hydrogen-bond between amine group (secondary or tertiary) in polymer backbone and water. This bond-breaking introduces a critical change in the roughness of the coating, which was observed using atomic force microscopy. We also show that the response temperature can be tuned, which opens up the possibility of designing country-specific self-cleaning exterior paints.