Rapid hybrid microwave cladding of SiO2/TiO2 sol–gel derived composite coatings

UV protection and coatings for plastics are important in many applications. The cladding of low microwave (MW) absorption composite coatings on high MW transparent plastic substrates is a challenge due to their disparate dielectric properties. Moreover, an uneven heat energy conversion within the composite creates an additional hurdle in producing a coating with good surface integrity. In this study, a protocol was developed to overcome these difficulties based on a hybrid approach. The adverse effect of temperature mismatch between the coating and substrate was reduced through a two-way susceptor-aided heating mechanism. Low MW absorbing sol–gel derived composite coatings consisting of silicon dioxide (SiO 2 ) and titanium dioxide (TiO 2 ) were successfully cladded on the surface of MW and visual light transparent polycarbonate to produce a clear protective coating with UV-resistance. Nanoindentation tests were conducted to assess the effectiveness of the proposed protocol. Significant enhancement in the surface elastic modulus and hardness were achieved. Schematic of hybrid MW cladding of sol–gel derived SiO 2 /TiO 2 coating on polycarbonate. The heat energy transferred to the sample is a combination of (1) the heat generated through MW coupling of the SiO 2 /TiO 2 coating and (2) the heat transfer by conduction, convection, and radiation from the heated. This process promotes hydrolysis and condensation reactions, leading to fast densification of the coating. Moreover, the difficulty of processing low microwave absorbing and microwave transparent materials simultaneously has been overcome. As a result, a crack-free SiO 2 /TiO 2 coating with enhanced surface mechanical properties can be produced within a minute.