Flexible phase change composites with enhanced thermal conductivity and mechanical properties for photothermal conversion and γ-rays shielding

The aqueous polyurethane/paraffin@lead tungstate@silicon dioxide (WPU/Pn@PWO@SiO2) phase change composites show the defects of poor thermal conductivity and photothermal conversion capacity, resulting in composites with poor photoresponse rates and slow thermal conversion, transfer, and storage. Herein, we have performed a novel tannic acid (TA)-assisted hydrophilic modification to functionalize graphene (G) nanosheets and construct polydopamine (PDA)-modified multi-shelled phase change microcapsules. Then, the tannic acid-modified graphene (TA-G) nanosheets and Pn@PWO@SiO2@PDA microcapsules were filled with WPU to obtain WPU/Pn@PWO@SiO2@PDA/TA-G (WPG) phase change composites. TA-G nanosheets have exhibited excellent hydrophilicity with a contact angle of 58.8°and dispersed well in the WPU. The synergistic effect of SiO2 and PDA shells has dramatically enhanced the leak-proof performance, thermal cycling stability and wettability of microcapsules. The multiple hydrogen bonding networks formed by PDA shell and TA-G nanosheets as well as WPU matrix effectively enhanced the mechanical properties of WPG composites. The thermal conductivity of the WPG-4 composite reached 0.778 W·m−1·K−1 at 4 % TA-G filling. The synergistic effect of PDA and graphene was utilized to greatly capture visible light for conversion, with a maximum photothermal conversion efficiency of 79.6 %. Furthermore, at 105.3 KeV and 86.5 KeV, respectively, the mass attenuation coefficients of WPG-2 composites reached 1.56 cm2/g and 1.28 cm2/g, exhibiting efficient γ-rays shielding properties. This multifunctional phase change composite shields against γ-rays while efficiently absorbing solar light to store and release latent heat for temperature regulation.