Superhydrophobic Silica Aerogels and Their Layer-by-Layer Structure for Thermal Management in Harsh Cold and Hot Environments

Abstract

Personal thermal management (PTM) materials have recently received considerable attention to improve human body thermal comfort with potentially reduced energy consumption. Strategies include passive radiative cooling and warming. However, challenges remain for passive thermal regulation of one material or structure in both harsh hot and cold environments. In this work, silica aerogels derived from sodium silicate were prepared through a solvent-boiling strategy, where hydrophobization, solvent exchange, sodium purification, and ambient pressure drying (HSSA) proceeded successively and spontaneously in a one-pot process. This strategy leads to the synthesis of superhydrophobic silica aerogels with extremely low energy consumption without out the use of an ion-exchange resin or low surface tension solvents. Silica aerogels possess a high specific surface area (635 m2/g), high contact angle (153°), and low thermal conductivity (0.049 W/m K). A layer-by-layer (LBL) structure including the silica aerogel layer and an extra phase change material layer was designed. The structure demonstrates dual-functional thermal regulation performance in both harsh cold (−30 °C) and hot (70 °C) environments, where the time to reach equilibrium is postponed, and the inner temperature of the LBL structure can be kept above 20 °C in harsh cold environments (−30 °C) and below 31 °C in harsh hot environments (70 °C). A proof-of-concept experimental setup to simulate the illumination of sunlight also proved that the inside temperature of a model car protected by the LBL structure was below 28 °C, while the outside temperature was 70 °C. In addition, these results are well supported by theoretical COMSOL simulation results. The findings of this work not only provide an eco-friendly approach to synthesize silica aerogels but also demonstrate that the LBL structure is a robust dual-functional PTM system for thermal regulation in both harsh hot and cold environments.

An intelligent cooling material modified with carbon dots for evaporative cooling and UV absorption

“…1b. The typical 19 The third absorption at about 324 nm originates from the n / p* edge transition. 20 According to the uorescence spectrum, the maximum emission wavelength of CDs is 674 nm.…”

“…1b. The typical absorption peak of CDs at 237 nm belongs to the π → π* transition in the cores, and the absorption peak at 275 nm belongs to the n → π* transition of CO. 19 The third absorption at about 324 nm originates from the n → π* edge transition. 20 According to the fluorescence spectrum, the maximum emission wavelength of CDs is 674 nm.…”

Aerogel‐Functionalized Thermoplastic Polyurethane as Waterproof, Breathable Freestanding Films and Coatings for Passive Daytime Radiative Cooling

“…The increase in the residual mass could be ascribed to SSA, which exhibits high thermal stability. [49][50][51]…”

A Trimode Thermoregulatory Flexible Fibrous Membrane Designed with Hierarchical Core–Sheath Fiber Structure for Wearable Personal Thermal Management

“…Phase change materials (PCMs) capable of absorbing and releasing heat energy are attractive for maintaining a constant temperature in the PTM field. However, the inherently solid rigidity and liquid leakage of PCMs hinder their applications in the wearable thermal regulation field. − Numerous form-stable strategies have been committed to improving the packaging efficiency of PCMs, such as the 3D aerogel network, − the polymer-cross-linked skeleton, − microencapsulation, − and others. The aforementioned methods based on capillary absorption in a porous structure still possess leakage threats at high temperature, and the other methods that depend on covalent cross-linking are prone to constrain the movement of molecular chains between amorphous and crystalline phases extensively, leading to deteriorated heat enthalpy of PCM composites.…”