Superhydrophobic and photoactive films on polymer surfaces

Transparent and flexible polymeric films might represent cheap and versatile materials for applications such as low cost solar cell covers. However, their use is limited by their low mechanical hardness and UV-light sensitivity. The use of oxide coatings has been proposed to enhance the mechanical properties and UV-resistance of polymers[1]. Oxide films might also impart self-cleaning or anti-stain properties to polymer surfaces. This might represent an innovative solution to a common issue for the service life of solar cells, i.e. the loss of incident light through scattering or absorption by accumulated dust. As a matter of fact, each g/m2 of dirt on cell covers reduces their efficiency up to 33%[2]. As installed solar panels are difficult to access, self-cleaning cell covers might be a viable solution. To achieve this goal, the main challenge to overcome is the development of low temperature syntheses for the deposition of active and adhesive oxide films over polymers. In this study, adhesive, antireflective, self-cleaning or anti-stain oxide films are deposited over transparent polymers by a two-step approach. First, the polymer surface is engineered to improve the oxide adhesion by providing a homogeneous distribution of suitable functional groups. Second, a low temperature synthesis is developed to obtain transparent, photoactive or superhydrophobic TiO2/SiO2-based films starting from a colloidal oxide suspension grown under microwaves irradiation. The obtained materials are characterized for their optical (UV-vis spectroscopy), mechanical (hardness and adhesion tests), and photocatalytic properties (stain removal). Further, durability tests under environmental conditions and accelerated aging under UV-light are performed.