Synthesis and properties of PI composite films using carbon quantum dots as fillers

Polyimide (PI) is widely used in the field of microelectronics because of its excellent thermal, mechanical, optical, and electrical properties. With the development of electronics and information industry, PI as a dielectric material needs to possess low dielectric loss. PI/carbon quantum dots (PI/CQDs) composite films with low dielectric loss were prepared by introducing CQDs into PI matrix. At 25°C and 1 kHz voltage, the dielectric loss of pure PI film is about 0.0057. The dielectric loss of PI/CQDs composite film is about 0.0018, which is about 68% lower than that of pure PI film. The dielectric loss of PI/CQD composite film is greatly reduced while the mechanical properties and thermal properties of PI/CQDs composite film roughly remain unchanged. Due to the cross-linking structure formed between CQDs and PI molecular chain, the relative movement of PI molecular chain is hindered.

Role of functionalized multiwalled carbon nanotubes on mechanical properties of epoxy-based composites at cryogenic temperature

In order to obtain multiwalled carbon nanotubes (MWNTs)/epoxy composites with good mechanical properties at cryogenic temperature, two methods were adopted to modify MWNTs. MWNTs were first treated by acid mixture (oxidized MWNTs, O-MWNTs) and then maleic anhydride (MA) and isophorone diisocyanate (IPDI) grafting was carried out. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses proved the effectiveness of acid mixture treatment and confirmed the grafting reaction of MA and IPDI with MWNTs. High-resolution transmission electron microscopy analysis indicates that MA and IPDI chain were grafted onto the MWNTs surface, creating a rigid covalent bond between MWNTs and epoxy resin and forming a thin layer. The tensile strength, Young’s modulus, and impact strength of composites at liquid nitrogen temperature (77 K) are all enhanced by the addition of MWNTs. Results of dynamic mechanical analysis indicated that introducing a small amount of functionalized MWNTs to epoxy can enhance their storage modulus at 77 K and glass transition temperature of composites. The results indicated that surface-modified MWNTs can be effectively utilized to improve the properties of epoxy-based composites at cryogenic temperature.