Preparation and dielectric properties of surface modified TiO₂/PEN composite films with high thermal stability and flexibility

A series of surface modified titanium dioxide (TiO₂)/polyarylene ether nitriles (PEN) composite films with different modified TiO₂ contents were prepared by solution casting method combined with ultrasonic dispersion technology. TiO₂ particles were successfully surface modified by PEN–COOH polymer previously, which was confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Besides, SEM images of composite films revealed that the interfacial adhesion between surface modified TiO₂ particles and the PEN matrix was effectively improved because of their common cyano groups and similar structure units. Furthermore, thermal, mechanical and dielectric characterizations showed that the composite films possess excellent thermal properties and flexibility as well as good dielectric properties, their glass transition temperatures were as high as 223 °C and the initial decomposition temperatures were all above 480 °C. In addition, it was found that the tensile strength of modified TiO₂/PEN composites was better than raw TiO₂/PEN composites. More importantly, the dielectric constant of composite films increases linearly with increment of the surface modified TiO₂ particles content. When the mass fraction of modified TiO₂ particles reached 40 %, the dielectric constant of the composite film increased to 7.9 (1 kHz), while the dielectric loss is just 0.028 (1 kHz).