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Functional Inorganic Materials and Devices
Hierarchical Cellular Structured Ceramic Nanofibrous Aerogels with Temperature-Invariant Superelasticity for Thermal Insulation Lvye Dou, Xinxin Zhang, Xiaota Cheng, Zongmin Ma, Xueqin Wang, Yang Si, Jianyong Yu, and Bin Ding ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b10018 • Publication Date (Web): 22 Jul 2019 Downloaded from pubs.acs.org on July 23, 2019
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ACS Applied Materials & Interfaces
Hierarchical
Cellular
Structured
Ceramic
Nanofibrous Aerogels with Temperature-Invariant Superelasticity for Thermal Insulation Lvye Dou†, Xinxin Zhang†, Xiaota Cheng†, Zongmin Ma‡, Xueqin Wang‡,//, Yang Si*,†,‡,//, Jianyong Yu// and Bin Ding*,†,‡,// †
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of
Textiles, Donghua University, Shanghai 201620, China ‡
College of Materials Science and Engineering, Donghua University, Shanghai 201620, China
//
Innovation Center for Textile Science and Technology, Donghua University, Shanghai
200051, China * Correspondence and requests for materials should be addressed to Y. S. (
[email protected]), B. D. (
[email protected]) KEYWORDS: electrospun nanofibers, ceramic aerogels, hierarchical cellular structure, temperature-invariant superelasticity, thermal insulation
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ABSTRACT
Silica aerogels are attractive for thermal insulation due to their low thermal conductivity and good heat resistance performance. However, the fabrication of silica aerogels with temperatureinvariant superelasticity and ultralow thermal conductivity has remained extremely challenging. Herein, we designed and synthesized a hierarchical cellular structured silica nanofibrous aerogel by using electrospun SiO2 nanofibers (SNFs) and SiO2 nanoparticle aerogels (SNAs) as the matrix and SiO2 sol as the high-temperature nanoglue. This pathway leads to the intrinsically random deposited SNFs to assemble into fibrous cellular structure, and the SNAs are evenly distributed on the fibrous cell wall. The unique hierarchical cellular structure of the ceramic nanofibrous aerogels endows it with integrated performances of the ultralow density of ~0.2 mg cm−3, negative Poisson’s ratio, ultralow thermal conductivity (23.27 mW m-1 K-1), temperature-invariant superelasticity from -196 to 1100 °C, and editable shapes on a large scale. These favorable multi-features present the aerogels ideal for thermal insulation in industrial, aerospace, and even extreme environment.
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ACS Applied Materials & Interfaces
1. INTRODUCTION Emergency protection against thermal runaway, heat insulation in extreme environment, improving energy efficiency, and avoiding excessive heat dissipation are currently playing a vital role in the field of energy conservation and process safety protection. 1, 2 Based on this, numerous thermal insulators, including polymeric insulators,3-7 carbon aerogels,8-10 and ceramic nanoparticle aerogels11-13 have been used in thermal barrier areas at different temperature levels.14-15 Among them, ceramic aerogels are famous for their comprehensive features of high porosity, low density, and ultralow thermal conductivity, exhibiting the desirable potential to be used as high-temperature heat barrier.16-20 However, the fragile feature caused by the inefficient structure continuity of inherent “pearl necklace-like microstructure” greatly limited the practical application of ceramic nanoparticle aerogels.21, 22 Up to now, much efforts have been done to improve the elasticity of ceramic nanoparticle aerogels, including chemical vapor deposition or atomic layer deposition,23, 24 cross-linking with organic polymers,25, 26 freeze-casting or supercritical drying of the sol precursors.27-30 However, the structure of the most existing ceramic nanoparticle aerogels is still easily destroyed under external conditions, and its brittle nature remains unresolved. Therefore, ceramic aerogel with novel structure, which could endow it with superior high-temperature thermal resistance and recoverable compressibility under harsh conditions is in urgently demand.31-34 Recently, as a new kind of aerogel, fibrous aerogels consist of nanotube, nanowire or nanofiber have emerged. At the same time, ceramic fibrous aerogels with elastic resilience of ~30% strain have been developed by assembling flexible one-dimensional materials into a continuous, three-dimensional (3D) fibrous structure, including oxide ceramic (TiO2, ZrO2, and BaTiO3) fibrous sponges,22,
35
SiC and α-Si3N4 fibrous
aerogels,36, 37 hollow-tube Al2O3 microlattice,33 and BN fibrous aerogels.38,
39
But the
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micro-sized diameter of these units always lead to relatively poor thermal insulation performance, which seriously hindered their practical application. Taking advantages of the small fiber diameter, high specific ratio, robust stability, and low cost, electrospun ceramic nanofibers have attracted much attention, and a series of flexible ceramic nanofibers have been proposed in our previous work.40, 41 Based on this, a simple and scalable approach for preparing ultralight ceramic nanofibrous aerogels with superelasticity (elastic resilience >80% strain) is established by using ceramic nanofibers as matrix.33 This method may provide significant idea to the development of ceramic nanofibrous aerogels in a lightweight, resilient, and structurally adaptive form. However, the unitary fibrous cell wall structure with pore size of 1~3 μm cannot effectively prevent the gas phase conduction, leading to a higher thermal conductivity (32 mW m-1 K-1) than that of ceramic nanoparticle aerogels (
