Developing Composite Aerogels with Super Heat Barrier and Sunlight Reflection

Abstract

Recent advances in aerogel technology have garnered significant interest in exploring new composite materials mainly due to their exceptional properties that make them highly suitable for efficient radiative cooling applications. Leveraging material with exceptional solar reflectance and strong thermal emittance achieves sub-ambient temperature drop. Moving beyond traditional scatterer particles to fabricate composite, a layered 2D nanomaterial possesses exceptional thermal, optical, and mechanical properties. Among them, hexagonal boron nitride (h-BN) is distinguished by a combination of the wide band gap, superior thermal stability up to 800 °C, mechanical stiffness, and infrared emissivity. This thesis introduces a novel approach to exfoliating h-BN using a greener and more convenient approach, a high- pressure homogenizer (HPH). Here, we synthesized a 3D porous scaffold based on high-quality prepared h-BN flakes and experimentally evaluated their radiative cooling performance, along with a comprehensive surface morphology and mechanical properties analysis. Three types of polymers, PVA, CMC, and HEC, with different exfoliated h-BN content (0wt%, 5wt%, 10wt%, 20wt%, and 50wt%) were characterized. The XRD of h-BN nanosheets proves the success of the peeling process, a highly crystalline (002) plane, exhibiting a blue shift from 26.82o to 26.72o with a diminishing of other peaks. Raman spectroscopy also revealed a blue shift corresponding to the in-plane vibration of the hexagonal lattice from 1366.01 cm-1 to 1369.37 cm-1. Among all composite aerogels, the PVA/ehBN attained the highest average weighted solar reflectance at a 20wt% of about 95.5±1.32%. The observed cross-sectional microstructure of unidirectional frozen aerogel showed the transformation from the cellular open porous structure into closed compacted elongated pores structure. Moreover, the longitudinal structure changed from a highly linked strand-like structure into a disturbance in the lamellar growth with high loading of h-BN flakes. At 60% strain across all polymers, PVA aerogel had exceptional compression strength between the lowest to highest nanofiller loading, raising from ~40 KPa to a stress exceeding 100 KPa.

Date of Award	9 May 2025
Original language	American English
Supervisor	Yahya Zweiri (Supervisor)