Important progress in boron nitride aerogel film and its Phase chance composite

    Aerogel, as an ultralight solids with a typical porous network and super-low thermal conductivity, could be a promising super thermal insulation and thermal protection materials for aerospace, buildings, electric vehicles, and portable electronics, etc. However, almost aerogel are in bulk form without the character of thin and flexible. Meanwhile, it is difficult to post processing, such as cutting and compress, due to its poor mechanical strength. Therefore, the design of aerogel in low dimensional form is still a challenging, which restrict the using of aerogel in thermal management, such as the thermal control requirement of the portable 5G electronic devices of the future.

    In order to achieve the thin design of aerogel, our team collaborated with Jianhe Liao’s group from Hainan University, finding an easy method to design thin aerogel with an aerogel precursor which can be cut and compress. The bulk melamine diborate (M·2B) aerogel-like monolith was synthesized based on the hydrogen bonding-directed assemblies of boric acid (B) and melamine (M), which can be adjust by the ratio of water and tert-butanol in co-solvent systems. The M·2B aerogel is formed by the wrapped around of nanoribbons. It has good processability with cut and compress. After simple cutting, compress and high-temperature pyrolysis, a flexible and free-standing boron nitride (BN) aerogel film is obtained, as shown in Figure 1. The thickness, density, shape and size of BN aerogel can be adjusted via the control of related technological parameter. Moreover, such BN aerogel can be bend under room temperature, liquid nitrogen and flame, showing good mechanical flexibility.

Figure 1 Photograph of M·2B slice and the M·2B monolith (a-c). Relationship between the thickness of M·2B film and stress (d). Bent BN aerogel film at room temperature (e), in liquid nitrogen (f), and on the flame (g). Typical SEM images of the BN aerogel film (h,i).

    Furthermore, the phase change material was embedded into the porous network of BN aerogel film, and the white BN-paraffin phase change composite film was fabricated for advanced thermal management in portable electronics. Aerogel have remarkable capillarity, which can effectively confine the melted organic solid-liquid phase variable material. The BN-paraffin composite film have good shape stability, high enthalpy and better thermal conductivity than the current commercial flexible phase change materials, as shown in figure 2.

Figure 2 (a) Photograph of BN aerogel/paraffin composite film. (b-d) SEM images of the BN-paraffin composite film. (c) TG curves of the pure paraffin, BN aerogel film, and BN-paraffin composite film. (d) DSC curves of the pure paraffin and BN-paraffin composite. (e) Thermal conductivities of the BN aerogel film, paraffin, paraffin/BN film, and HeatSORB film.

    Aerogels and their phase change composites have the thermal control management capabilities as followings: (1) aerogel film have the character of thin and low thermal conductivity; (2) aerogel phase change film can keep the temperature of its self relatively constant under the variation temperature environment by absorbed and released of heat, realizing the confinement and modulation of thermal energy. Furthermore, to demonstrate the thermal insulation of BN aerogel film in the real electronics, the BN aerogel film was used as the thermal insulating film in a smart 5G phone (HUAWEI, Nova 7 SE 5G). Benefitting from the low thermal conductivity of aerogel, high-temperature stability, and the electrical insulation of BN, the BN aerogel film could serve as a good thermal insulator in portable electronic device to provide the thermal protection for functional units and human body, as shown in figure 3.

Figure 3 Schematic of thermal management mechanisms based on thermal insulation of BN aerogel film and thermal regulation of BN-PCM composite film.

    This work has provided design guideline for multifunctional thermal management films to optimize thermal protection effect to portable electronic, functional unit, or biological tissues. It is expected to realize diversified applications of thermal control management in advanced 5G portable electronic devices in the future.