Applications of flexible photothermal phase-change material and flexible silica aerogel composites in building thermal management: Preparation, properties, and thickness optimization

Building envelopes in cold regions suffer from low solar-thermal absorption, high heat loss, and poor conformability to complex curved surfaces. To address these issues, this study developed a composite insulation–photothermal conversion material consisting of a Flexible photothermal phase change material (FPPCM) and a Flexible Silica Aerogel (FSA) film. The FPPCM was fabricated using Styrene - ethylene - butene - styrene (SEBS) as the flexible skeleton, paraffin as the phase-change medium, and graphene as the photothermal enhancer. It exhibited a phase-change enthalpy of 187.96 J/g, with an enthalpy loss of less than 8.97% after 200 thermal cycles, and could withstand 180° bending without cracking. The FSA film showed a low thermal conductivity of 0.0218 W/(m·K), an average full-spectrum transmittance of 83.87% at a thickness of 1.0 mm, and favorable flexibility. Under 200–600 W/m 2 solar irradiance, the FPPCM–FSA composite increased the maximum chamber temperature by 12.68 °C compared to the conventional PCM–FSA system, a 37.0% improvement. Based on a heat transfer model, the aerogel thickness was found to synergistically regulate the net energy gain efficiency and the useful heat flux transmitted indoors. When the aerogel thickness was 1.5 mm, the useful indoor heat flux reached a maximum value of 196.5 W/m 2 , indicating the optimal thickness for thermal performance. When the thickness was 1.0 mm, the useful heat flux per unit cost reached the highest value of 192.3 W/m 2 , indicating the economically optimal thickness. This study provides a feasible material design for improving the thermal insulation and solar-thermal utilization performance of building envelopes, showing promising application potential.