Intense pulsed UV light treatment to design functional optical films from perhydropolysilazane: an alternative to conventional heat treatment processes

Perhydropolysilazane (PHPS) forms a thin layer by solution processing and converts to dense glass-like silica (SiOx) with excellent chemical resistance, adhesion, and optical properties. However, heat treatment methods for the conversion of PHPS into SiOx are not sufficient for its application to functional polymer films. In this study, our group developed an alternative process using irradiation by intense pulsed UV light (IPL) at low temperatures in an air environment. We prepared PHPS-derived SiOx layers using various exposure energies (4.2, 8.4, and 12.6 J cm−2) and then examined their chemical behaviors, compositions, conversion rates, and refractive indices. The resulting SiOx layer exhibited a 100% conversion rate similar to that of a heat-treated silica layer (600 °C) and a refractive index (RI) value identical to that of amorphous SiO2 (1.45). Moreover, the final SiOx thin layer (160 nm ± 0.7 nm) on a polyethylene terephthalate (PET) film had a transmittance of 90.7% and a pencil hardness of 4H at a load of 750 g. The mean hardness and elastic modulus for the SiOx layer were 3.25 GPa, and 27.98 GPa, respectively, values similar to those of SiOx layers formed by roll-to-roll vacuum deposition. Furthermore, the final SiOx thin layer exhibited no cracks after 100 K bending cycles. Overall, we established that the IPL process is effective for converting PHPS into SiOx layers on flexible polymer films that have good hardness, elastic modulus, and transparency. It can be applied in large-scale roll-to-roll manufacturing processes to generate functional materials for the optical film industry.