Aerogel is an ultra-light solid material with a three-dimensional porous network structure. It has ultra-low thermal conductivity and can be used as a super thermal insulation material to play an important role in aerospace, building energy conservation, electric vehicles and portable electronic equipment. . However, most of the current aerogels are in the form of macroscopic blocks, and do not have the characteristics of slenderness, lightness, and flexibility. On the other hand, the weak mechanical strength of aerogel materials makes subsequent processing (such as cutting and compression) relatively difficult. Therefore, the design of the low-dimensional macroscopic form of aerogel still has certain challenges, which restricts the function of aerogel material in confined space thermal management, such as the actual thermal control of the emerging 5G portable/wearable electronic system in the future need.

In order to realize the thin and light design of aerogel materials, a cutable and compressible aerogel precursor was found, and a simple design method for thin and light aerogel was developed. Through the water-tert-butanol co-solvent system, the hydrogen bond assembly of boric acid and melamine is regulated to obtain the melamine-diborate (M·2B) aerogel bulk material formed by entangled and overlapped nanobelts. The aerogel block has the characteristics of being cuttable and compressible, and has good processability. After simple cutting, compression and subsequent high-temperature pyrolysis, a flexible, self-supporting boron nitride aerogel film was successfully obtained, as shown in Figure 1. Through the adjustment of process parameters, the thickness, density, shape and size of the boron nitride aerogel film can be effectively controlled, and the obtained boron nitride aerogel film can be bent at room temperature, liquid nitrogen and flame, showing Good mechanical flexibility, as shown in Figure 1.

Figure 1 Cutability (a-c), compressibility (d) of melamine-diborate aerogel bulk material, mechanical flexibility (c-g) and micro-morphology (h-i) of boron nitride aerogel film.

In addition, the above-mentioned boron nitride aerogel film is used as a support material to successfully obtain a boron nitride aerogel phase change film. Thanks to the significant capillary force of the aerogel itself, it can effectively restrain and confine the organic solid-liquid phase change material in the molten state, and prevent the leakage of the molten phase change material. The obtained boron nitride aerogel film exhibits good shape stability; the obtained boron nitride aerogel phase change composite film has a high phase change enthalpy, and has a thermal conductivity better than that of current commercial flexible phase change materials. as shown in picture 2.

Figure 2 Optical photographs of boron nitride aerogel phase change composite films at different temperatures (a), the micro morphology (b-d) and thermal properties (e-g) of the film.

Aerogels and their phase change composite materials have the following thermal management potentials: 1) Aerogel films have the characteristics of low thermal conductivity, lightness and thinness, which can isolate heat in confined spaces; 2) Aerogel phase change composite films It can absorb or release heat reversibly in a temperature-changing environment, and maintain its own temperature relatively constant to realize the limitation and modulation of thermal energy.

At present, the feasibility of the boron nitride aerogel film and its phase-change composite film in the diversified thermal management of advanced electronic systems (such as portable, wearable, 5G, etc.) has been preliminarily explored, and based on heat insulation and Two thermal control management strategies of thermal energy modulation and their application forms and scenarios are shown in Figure 3. Aerogel film and phase change composite film can effectively change and control the direction of heat flow, prevent heat from spreading to nearby biological tissues and other functional units, provide a comfortable operating environment for electronic systems, and provide a comfortable environment for the human body using electronic devices Wear or use environment.

Figure 3 Schematic diagram of thermal management of aerogel film and phase change composite film in a portable electronic system.

This research work provides theoretical support and guidance for the lightweight and thin design of aerogel materials and the diversified management of thermal energy in confined spaces. It is expected to realize the diversified application of thermal management in advanced 5G portable electronic devices in the future.