气凝胶在隔热防护领域中的研究进展

张飞飞; 王峰; 王万安; 景卓元; 姜笑天; 徐磊

气凝胶在隔热防护领域中的研究进展

1.
中国人民解放军32181部队, 陕西西安 710000
2.
陆军勤务学院, 重庆 400000

详细信息

通讯作者:
徐磊，硕士研究生，高级工程师，研究方向为军需专业　E-mail: 574238301@qq.com

中图分类号: TB332
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- 文章访问数: 15
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出版历程
- 收稿日期: 2024-07-21
- 修回日期: 2024-08-24
- 录用日期: 2024-08-30
- 刊出日期: 2025-06-14

Advances on thermal insulation applications of aerogels

1.
32181 Unit of the Chinese People's Liberation Army, Xian 710000, Shanxi, China
2.
Army Logistics Academy, Chongqing 400000, China

摘要

摘要:
气凝胶独特的三维纳米网络结构使其同时具有超低密度和超低热导率的特性，是理想的轻量化隔热保温材料，在微电子、航空航天等对重量要求严格的领域行业具有很大吸引力，激起科研人员广泛的研究兴趣，并对该领域进行了大量的科研工作。本综述首先分析了气凝胶材料的制备方式，重点论述了溶胶-凝胶法、分子路线法、静电纺丝法、3D打印等方法并对气凝胶材料在隔热领域的应用进行了总结；后续又对气凝胶的材料选用等方面进行探讨，最后展望和分析气凝胶的未来研究重点方向。
- 气凝胶 /
- 隔热保暖 /
- 溶胶-凝胶 /
- 增材制造 /
- 气凝胶材料
Abstract:
The unique three-dimensional network of aerogel endowed it with characteristics of ultra-low density and ultra-low thermal conductivity, These characteristics made it to an ideal lightweight thermal insulation material. And has highly attractive in fields of microelectronics, aerospace and other fields with strict weight requirements. Therefore, it sparks extensive research interest of researchers work in this field. This review first analyzes the preparation methods of aerogel materials, mianly focus on sol-gel method, molecular route method, electrospinning method, 3D printing and other methods in the thermal insulation application of aerogel. Subsequently, discussions on material selection of aerogel are carried out. Finally, a brief summary of prospect and analysis on the future research directions of aerogels are made.
- aerogel /
- thermal insulation /
- sol-gel /
- drying method /
- aerogel material

HTML全文

目前，全球变暖带来的负面效应极大地影响了人类的生产生活^[1-2]，能源的过度消耗和匮乏使得环境问题进一步增加，如何做好热管理是目前面临的主要问题^[3-5]。地球表面温度为300 K，而外太空平均温度为3 K^[6-7]，根据热力学第二定律，地球上物体的热量由于热量差可以通过辐射的方式将热量传递到外太空。因此，辐射制冷技术是地球上的物体通过“大气窗口”波段(8~13 μm)将热量辐射到外太空^[8-10]，以此实现自身降温冷却的过程。

虽然辐射制冷材料在节能环保方面显示出极大的应用潜力^[10]，但现有材料多为白色或银白色，外观单调，利用率极低。染料会使材料的表面颜色发生改变，但染料的可见色会吸收热量，并在近红外波段内吸收额外的热量^[11-12]，降低了材料本身的制冷效果。到目前为止，克服这一问题的主要策略是提高在可见光区域内的反射率和在“大气窗口”波段(8~13 μm)的发射率^[13-16]。为避免染料吸收热量的现象，结构色辐射制冷材料引发人们的广泛关注^[17-18]。利用硅蛋白石可以制备具有结构色变化的辐射制冷材料，但这种方法不能实现亚环境冷却^[19]，并且生产工艺和条件复杂且苛刻，很难进行大批量生产和应用。

纤维素纳米晶体(CNC)是刚性的棒状颗粒，长度为数十至数百纳米，直径可以达到数十纳米^[20]，具有结晶度高、降解性好等特点。CNC可以从棉花、木材和纸浆等可再生资源中提取，具有成本低、绿色、可持续等特性^[21-23]。CNC可以在水中自发地组织成手性向列结构的液晶相，这种有序结构在干燥过程中可以得到保留，直至得到具有手性向列结构的CNC薄膜^[24]。双折射的CNC纳米棒在薄膜中呈现的螺旋式排列会使纳米结构的折射率产生周期性的变化，进而引起对可见光的强烈反射^[25]。因此，结构色的调节与螺旋结构的周期性密切相关。

目前已有研究致力于制造色彩更为丰富的纤维素辐射制冷材料。Shanker等^[26]通过将CNC自组装成结构色薄膜，与硅片基底结合，得到了一种结构色辐射制冷装置。通过控制CNC/甘油(GLU) 的质量比得到颜色由蓝紫色转变为红色的复合薄膜。结构色复合薄膜表现出在太阳光谱范围内低吸收率和“大气窗口”内高发射率，且绿色和红色样品降温效果可达9℃左右，蓝紫色样品的降温效果可达6℃左右，为制备纤维素结构色辐射制冷薄膜提供了研究基础。

本文将CNC与聚乙二醇(PEG)复合，通过自组装方法制备了高太阳光反射率和在“大气窗口”波段高发射率的结构色薄膜。通过控制CNC与PEG的质量比，调控复合薄膜的结构色，以实现不同波段的热辐射率调控。探究不同含量PEG的添加对CNC复合结构色薄膜的结构、光学性能及制冷性能的影响。并将复合结构色薄膜粘贴到醋酸纤维素滤膜上制备成双层复合膜，进一步探究双层复合膜的辐射制冷效应。

1. 实验材料及方法

1.1 原材料

醋酸纤维素：上海兴亚净化材料厂；浓硫酸(H₂SO₄₎：分析纯，阿拉丁世纪有限公司；聚乙二醇400：分析纯，天津市科密欧化学试剂有限公司。

1.2 实验过程

CNC的制备：利用酸水解法制备CNC，将200 mL 64%硫酸溶液缓慢倒入25 g硫酸盐漂白针叶浆中，在45℃的水浴加热中搅拌1 h，后加入大量蒸馏水来终止水解反应。静置2~3 d，去除上清液，加入去离子水通过高速离心机 (CT14D型，上海天美仪器有限公司) 进行多次离心洗涤。得到的CNC悬浮液，将CNC在去离子水中透析，直至pH为中性。最后将CNC悬浮液浓缩至3wt%，冷藏备用。

CNC/PEG复合薄膜的制备：称取聚乙二醇5.0 g，加入45 g超纯水中，在室温搅拌1 h，得到质量分数10wt%的聚乙二醇溶液。取一定量的质量分数为3wt%的CNC悬浮液超声5 min，取4份3.0 g CNC悬浮液分别与0.1000 g、0.2250 g、0.3857 g和0.6000 g PEG的溶液进行混合，将上述溶液充分搅拌2 h，后将混合液体倒入圆形容器中，室温缓慢蒸发2~3 d，得到PEG浓度为10wt%、20wt%、30wt%和40wt%的CNC/PEG复合结构色薄膜。按照聚合物的种类和含量对复合薄膜进行命名，分别为CNC/PEG-10%、CNC/PEG-20%、CNC/PEG-30%、CNC/PEG-40%，具体见表1。

表 1 纤维素纳米晶体/聚乙二醇(CNC/PEG)复合辐射制冷薄膜和CNC/PEG-醋酸纤维素(CA)结构色辐射制冷双层复合膜的命名

Table 1. Naming of cellulose nanocrystal/polyethylene glycol (CNC/PEG) composite radiative cooling films and CNC/PEG-cellulose acetate (CA) structure-colored radiation-cooled bilayer composite films

Sample	Mass fraction of CNC/wt%	Mass fraction of PEG/wt%	CA
CNC/PEG-10%	3	10	—
CNC/PEG-20%	3	20	—
CNC/PEG-30%	3	30	—
CNC/PEG-40%	3	40	—
CNC/PEG-10%-CA	3	10	0.0740 g
CNC/PEG-20%-CA	3	20	0.0740 g
CNC/PEG-30%-CA	3	30	0.0740 g
CNC/PEG-40%-CA	3	40	0.0740 g

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双层复合膜的制备：将不同质量比的复合结构色薄膜与醋酸纤维素膜用双面胶粘在一起，双面胶放在醋酸纤维素膜的边缘起固定作用，不会影响双层复合结构色薄膜的结构，双层复合结构色薄膜分别命名为CNC/PEG-10%-CA、CNC/PEG-20%-CA、CNC/PEG-30%-CA，具体见表1。

1.3 测试与表征

1.3.1 CNC/PEG复合膜的性能分析

采用Malvern Zetasizer nano ZS90测试CNC的Zeta电位和粒径。利用偏光显微镜(POM，XPF-550C，上海蔡康光学仪器公司)观察复合薄膜样品的液晶特性。使用反射光谱仪(UV-vis，HR4000 CG-NIR型，海洋光学公司)对薄膜进行反射光谱测试(可见光区域)。将复合薄膜用液氮进行脆断，用双面导电胶粘到截面制样台上，喷金60 s，利用扫描电子显微镜(SEM，JSM-7500F，日本电子株式会社)观察复合薄膜的横截面微观形貌。使用带有积分球附件的紫外-可见-近红外分光光度计(UV-VIS-NIR Spectrometer，美国Perkins Elmer公司)检测样品在300~2500 nm波长范围内的反射率变化。利用傅里叶变换红外光谱仪(FTIR，Nicolet-IS10，美国Thermo Fisher公司)检测样品在2.5~25 μm的波长范围内样品的吸收率变化。采用太阳光谱匹配良好的高功率氙灯(中教金源HXF300)来模拟太阳光照射，在聚苯乙烯(PS)泡沫箱子中裁剪一个1 cm×1 cm×1 cm的空腔，将薄膜或复合薄膜放置在空腔中固定，利用聚乙烯薄膜覆盖泡沫箱，消除环境热对流影响。将多通道温度计(JINKO，JK804)与两个k型热电偶进行连接，一个k型热电偶测试复合薄膜覆盖下空腔的内部温度，另一个k型热电偶用来测量聚乙烯膜覆盖下的装置内的环境温度。由于CNC/PEG-40%复合薄膜在表征过程中会吸收环境的水分，手性结构发生润胀，螺距在实际测量中会发生变化，不利于复合薄膜在实际环境中的应用，因此后续将不会对CNC/PEG-40%复合薄膜进行扫描电镜、光谱学和辐射制冷性能的测试与分析。

1.3.2 双层复合膜的性能分析

将醋酸纤维素膜用导电胶粘贴到水平制样台上，喷金60 s，利用扫描电子显微镜观察醋酸纤维素薄膜的表面形貌。在同一氙灯光源照射下，观察不同样品在红外热成像仪(FTIR-E390，美国FLIR SYSTEMS公司)下的温度变化。利用上述自组装装置分别测量双层复合薄膜下方温度及被聚乙烯膜覆盖的整个装置内的环境温度。利用实验室自组装装置对样品进行户外降温性能测试，将室内自组装降温性能测试装置放置在用铝箔纸包裹的纸壳箱中，整体放置在泡沫箱上，用湿度计记录测试过程中的环境湿度变化。

2. 结果与讨论

2.1 纤维素纳米晶的电位粒径分析

图1为CNC的TEM图像、粒径分布和电位曲线，酸水解法制备的CNC具有棒状形态，平均粒径为144.1 nm (图1(b))。在水解过程中，CNC表面形成较多的负电荷，Zate电位高达−32.2 mV (图1(c))。CNC表面较多的负电荷会促进静电排斥作用，使CNC溶液的稳定性增强，为进一步制备结构色复合薄膜奠定基础。

图 1 (a) CNC的TEM图像；(b) CNC的粒径分布；(c) CNC的电位曲线

Figure 1. (a) TEM image of CNC; (b) Particle size distribution of CNC; (c) Potential curve of CNC

下载: 全尺寸图片幻灯片

2.2 纤维素纳米晶复合薄膜结构色光学特性分析

图2(a)~2(d)是PEG含量不同的复合薄膜光学照片。随着PEG含量的增加，薄膜反射颜色发生红移，逐渐由蓝绿色转变为红色。因此，复合薄膜的结构色红移现象与PEG的含量相关。通过对紫外-可见反射光谱(图2(e))分析可得，随着PEG含量的增加，4种复合薄膜分别在427 nm、487 nm、576 nm和654 nm处存在清晰的高峰，复合薄膜反射光谱中的最高峰发生红移，与薄膜结构色的红移相对应。通过图2(f)可知，复合薄膜通过反射可见光和发射热量来实现自身降温，为后续辐射制冷的研究提供理论基础。

图 2 ((a)~(d)) CNC/PEG-10%、CNC/PEG-20%、CNC/PEG-30%、CNC/PEG-40%的光学图像；(e) CNC/PEG的紫外-可见反射光谱图；(f)复合薄膜辐射制冷示意图

Figure 2. ((a)-(d)) Digital photographs of CNC/PEG-10%, CNC/PEG-20%, CNC/PEG-30%, CNC/PEG-40%; (e) UV-vis reflection spectra of CNC/PEG; (f) Composite film radiative cooling schematic

下载: 全尺寸图片幻灯片

2.3 纤维素纳米晶复合薄膜微观形貌分析

图3(a)~3(c)为PEG含量不同复合薄膜的横截断面扫描电镜图。当PEG含量为40%时，复合薄膜会吸收环境中的水分，手性结构发生润胀，螺距在实际测量中会发生变化，因此只对PEG含量为10%~30%的CNC/PEG复合薄膜进行扫描电镜的研究，不对CNC/PEG-40%复合薄膜进行扫描电镜的测试与分析。纯CNC薄膜具有周期性的层状结构，CNC通过逆时针方向旋转后形成了左旋的手性向列螺旋结构，这种左旋的手性向列结构反射特定波长的左旋圆偏振光，从而使复合薄膜表现出独特的虹彩色。聚合物的加入并不会改变CNC原有的手性向列结构，随着聚合物含量的增加，CNC手性向列结构的螺距明显增加。布拉格方程式中手性向列的螺距(P)定义为CNC棒状颗粒旋转360°产生的层间距，在电镜图(SEM)中表现为相邻两层结构的间距。

图 3 不同PEG含量的复合薄膜横截面电镜图像

Figure 3. Cross-sectional electron microscope images of composite films with different PEG contents

下载: 全尺寸图片幻灯片

CNC/PEG复合薄膜的反射光遵循布拉格方程：

$\mathit{\lambda =nP\cos(\theta )}$

(1)

其中：λ为反射波长；n为薄膜的平均折射率；θ为入射角；P为手性向列结构的层间距。因为CNC和PEG的折射率相似，分别为1.41和1.44，所以薄膜的平均折射率(n)可以认为是常量，当入射角(θ)恒定时，λ取决于手性向列结构的螺距P。图3(a)~3(c)的平均螺距分别为0.30、0.36和0.46 μm。随着平均螺距P的增加其反射波长λ也逐渐增大，主要原因是在加入PEG后，PEG高分子进入到CNC手性向列结构中，导致CNC手性向列结构的螺距P增大，复合薄膜颜色红移。

2.4 纤维素纳米晶复合薄膜折射现象

图4是PEG含量不同的复合薄膜偏光显微镜(POM)图像。通过观察图4(a)~4(d)可以得知薄膜具有明显的双折射现象，高倍POM图像(图4(e)~4(h))可以看出其具有明显的指纹结构，这说明CNC/PEG在干燥过程中CNC自组装了手性向列结构，并且在完全成膜后，仍然保留其手性向列结构。因此，适量PEG的加入并不会破坏CNC自组装所形成的手性向列结构。复合薄膜的指纹结构的纹理间隔随着PEG含量的增加逐渐变宽，分别为2.05 μm、2.33 μm、2.84 μm和3.38 μm，颜色由蓝绿色逐渐转化成蓝红色。PEG的添加占据了手性向列结构CNC之间的空间，导致螺距P增大，从而发生红移。因此，通过对POM结果分析，证明了PEG的添加不会破坏CNC的手性向列结构和双折射现象，控制PEG含量可以有效调控CNC手性向列层间距，进而调控复合薄膜结构色的变化。

图 4 不同PEG含量的复合薄膜的偏光显微镜图像

Figure 4. Polarized light microscopy images of composite films with different PEG contents

下载: 全尺寸图片幻灯片

2.5 纤维素纳米晶结构色复合薄膜和双层复合薄膜的光谱学分析

由基尔霍夫定律可知，样品的发射率(T)等同于吸收率(A)。通过观察图5(a)可知，在室内湿度为42%时，样品在大气窗口波段(8~13 μm)都有较高的发射率，其中当PEG的含量为30%时，复合薄膜的发射率最高可达93.0%，这样可以最大限度的向天空辐射红外热量。CNC/PEG复合薄膜具有高发射率，这是由于O—H (6.9~7.6 μm)、C—O (7.6~9.5 μm)、C—H (11.1~14.3 μm)键在大气窗口范围(8~13 μm)内产生强烈的拉伸与弯曲振动所导致的。图5(b)是PEG含量不同的复合薄膜在太阳波段(0.3~2.5 μm)范围内太阳光反射率曲线，结构色复合薄膜在近红外范围内的反射率最高可达68.5%。随着PEG的含量增加，其反射率也随之变高。

图 5 不同PEG含量的复合薄膜：(a)发射率曲线；(b)在可见光范围内的反射率曲线

Figure 5. Composite films with different PEG contents: (a) Emissivity profile; (b) Reflectivity profile in the visible light range

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图6为不同PEG含量的双层复合制冷膜的发射率曲线和在可见光范围内的反射率曲线。通过观察图6(a)可知，在室内湿度为42%的测量环境下，双层复合膜在大气窗口的发射率高于醋酸纤维素膜的发射率，随着PEG含量的增加双层复合膜的发射率也逐步提高，当PEG含量为30%时，双层复合膜的发射率最高可达68.0%。图6(b)是PEG含量不同的双层复合膜在太阳波段(0.3~2.5 μm)范围内的太阳光反射率曲线，在近红外范围内的反射率最高可达91.8%。

图 6 不同PEG含量的双层复合制冷膜：(a)发射率曲线；(b)在可见光范围内的反射率曲线

Figure 6. Bilayer composite films with different PEG contents: (a) Emissivity profile; (b) Reflectivity profile in the visible light range

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2.6 纤维素纳米晶复合结构色薄膜和双层复合薄膜的辐射制冷性能分析

图7(a)为室内氙灯模拟图，利用100 mW/cm²高功率氙灯来照射，不仅可以模拟太阳光照射还可以将光均匀地分布在样品表面。图7(b)为用来测量样品温度及装置内空气温度的自组装装置，聚乙烯(PE)薄膜既可以保证氙灯的光照射到装置内部，又可以减少热对流对辐射制冷结果的影响。由图7(c)、图7(d)可知，将氙灯打开后，PE薄膜覆盖的装置内部温度迅速上升，在5 min后样品逐渐达到热稳定状态。当温度逐渐趋向平衡时，薄膜下方温度明显低于PE覆盖装置内的空气温度，不同结构色CNC/PEG复合薄膜辐射制冷性能相似，薄膜平均降温可达3.4℃。

图 7 (a)室内氙灯模拟装置图；(b)自组装温度测量装置图；CNC/PEG-10%和空气(c)、CNC/PEG-30%和空气(d) 温度对比图

Figure 7. (a) Photos of indoor xenon lamp simulation device; (b) Self assembling temperature measuring device; Temperature comparison of CNC/PEG-10% and air (c), CNC/PEG-30% and air (d)

PE—Polyethylene; IR—Infrared spectroscopy

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图8(a)~8(c)为不同纤维素基底在同一光源照射下的红外热成像图。在氙灯的照射下，采用红外热成像观察5 min，可以看出，醋酸纤维素薄膜的表面温度最低，滤纸的表面温度略高于醋酸纤维素薄膜，而A4纸的表面温度最高。通过观察醋酸纤维素的SEM图像(图8(d))可知，醋酸纤维素膜具有多孔结构，可以有效地反射可见光。图8(e)为醋酸纤维素膜下温度与环境温度对比曲线，膜下温度平均比环境温度低15℃左右。综上表明，醋酸纤维素薄膜具有良好的辐射降温能力，是作为双层复合薄膜的较优选择。

图 8 ((a)~(c))醋酸纤维素膜(CA)、滤纸和A4纸红外热成像图；(d) CA膜表面电镜图；(e) CA与空气温度对比图

Figure 8. ((a)-(c)) Infrared thermograms of cellulose acetate (CA) film, filter paper and A4 paper; (d) SEM image of CA film surface; (e) Temperature comparison of CA and air

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利用红外热成像分别观察CNC/PEG-20%、CNC/PEG-20%-CA和带有蓝色涂料的CA薄膜在相同时间和相同光照下其表面的降温能力，如图9(a)~9(c)所示。结果可知，CNC/PEG-20%-CA的表面降温能力较强，CNC/PEG-20%的降温能力次之，而带有蓝色涂料的CA薄膜的表面降温能力最差。通过分析CNC/PEG-20%和带有蓝色涂料的CA薄膜的温度曲线(图9(d)、图9(e))，进一步证实双层复合薄膜具有良好的制冷性能。由图9(f)、图9(g)可知，PE薄膜覆盖下装置内的空气温度与双层复合制冷膜下方温度的起始温度大致相同，氙灯打开后，两者温度迅速上升，5 min后双层复合制冷膜下方温度与装置内空气温度逐渐达到热稳定状态。当温度逐渐趋向平衡时，双层复合制冷膜下方温度远低于装置内空气温度，双层复合膜的辐射制冷性能几乎不受PEG含量的影响，双层复合薄膜平均降温可达14.3℃，双层复合膜的降温性能优于复合薄膜的降温性能。实验结果表明：CNC/PEG复合薄膜平均可降温3.4℃左右，醋酸纤维素膜是作为双层复合膜的理想基底，双层复合制冷膜的降温性能优于复合薄膜，平均降温可达14.3℃左右。

图 9 ((a)~(c)) CNC/PEG-20%、CNC/PEG-20%-CA与带有蓝色涂料的CA薄膜红外热成像图；带蓝色涂料的CA和空气(d)、CNC/PEG-20%-CA和空气(e)、CNC/PEG-10%-CA和空气(f)、CNC/PEG-30%-CA和空气(g)温度对比图

Figure 9. ((a)-(c)) Infrared thermograms of CNC/PEG-20%, CNC/PEG-20%-CA and and CA films with blue coatings; Temperature comparison of CA with blue painting and air (d), CNC/PEG-20%-CA and air (e), CNC/PEG-10%-CA and air (f), CNC/PEG-30%-CA and air (g)

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图10(a)、图10(b)为测量CNC/PEG-30%-CA、CNC/PEG-30%及PE覆盖装置内空气温度的户外装置图，利用铝箔纸包裹整个装置以减少周围建筑物对装置热辐射的影响，在装置顶部覆盖一层PE膜来减少环境中的热对流及热传导对整个装置的影响，装置下方的泡沫箱用来隔绝地面对测量温度的热影响，利用热电偶分别记录样品覆盖空腔中的温度及PE膜覆盖下装置的空气温度。通过分析图10(c)可以看出，在平均温度为25℃，平均湿度51%的户外环境中，与PE覆盖装置中空气温度对比，复合薄膜可以实现平均2℃左右的降温效果，而双层复合薄膜可以实现平均6℃左右的降温效果。

图 10 ((a), (b))测试CNC/PEG-30%-CA、CNC/PEG-30%和空气的温差变化的户外装置图；(c) CNC/PEG-30%-CA、CNC/PEG-30%与空气的温差图

Figure 10. ((a), (b)) Diagram of an outdoor installation for testing the change in temperature difference between CNC/PEG-30%-CA, CNC/PEG-30% and air; (c) Temperature comparison of CNC/PEG-30%-CA, CNC/PEG-30% and air

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3. 结论

本文将纤维素纳米晶体(CNC)与聚乙二醇(PEG)以不同比例混合，采用自组装的方法制备了具有辐射制冷性能的结构色复合薄膜，将结构色复合薄膜与具有多孔结构的醋酸纤维素膜(CA)相结合，制备具有辐射制冷和结构色特性的双层复合膜。分别对复合薄膜和双层复合膜的性能进行分析，得出的结论如下：

(1) CNC/PEG复合薄膜具有手性向列结构和鲜艳的结构色，复合薄膜出现明显的双折射特性，随着PEG含量的增加，复合薄膜手性向列结构的螺距增大，反射波长随之发生红移，最终导致薄膜结构色的变化；

(2)对CNC/PEG复合薄膜和CNC/PEG-CA双层复合膜进行FTIR和UV-vis测试可知，复合薄膜在0.25~2.5 μm的波长范围内的反射率高达93.0%，双层复合膜反射率可达68.0%，复合薄膜在“大气窗口”(8~13 μm)范围内的发射率可达68.5%，双层复合膜发射率高达91.8%；

(3)在氙灯照射下，CNC/PEG结构色复合薄膜具有辐射制冷性能，与装置内空气温度对比，平均降温可达3.4℃左右。与具有多孔结构的醋酸纤维素膜结合，双层结构色复合薄膜的辐射制冷性能得到提升，平均降温可达14.3℃左右。在户外降温性能测试中，复合薄膜可以达到平均2℃左右的降温效果，双层复合膜可以达到平均6℃左右的降温效果。

图 1 传统液相制备方法^[9]

Figure 1. Traditional liquid phasereparation Processes^[9]

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图 2 气凝胶的溶胶-凝胶制备路线^[11]

Figure 2. Sol-gel preparation route for aerogels^[11]

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图 3 纳米构筑单元组装法路线示意图^[33]

Figure 3. Schematic diagram of the route of the nano-building unit assembly method^[33]

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图 4 超弹性纤维素纳米纤丝气凝胶的组装过程示意图及蜂窝结构^[48]

Figure 4. Schematic diagram of the assembly process and honeycomb structure of superelastic cellulose nanofibril aerogel^[48]

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图 5 陶瓷气凝胶超材料的结构设计与制造^[62]

Figure 5. Structure design and fabrication of the ceramic aerogel metamaterial^[62]

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图 6 半晶质ZAG的制造工艺和热学性能表征^[64]

Figure 6. Fabrication process and thermal characterization of hypocrystalline ZAGs^[64]

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图 7 常用气凝胶打印技术^[9]

Figure 7. Commonly employed printing technologies for aerogels^[9]

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图 8 喷墨打印SiO₂气凝胶微球工艺^[67]

Figure 8. Inkjet printing process of SiO₂ aerogel microspheres^[67]

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图 9 喷墨打印SiO₂气凝胶薄膜工艺^[74]

Figure 9. Process of inkjet printing SiO₂ aerogel film^[74]

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图 10 (a) 直接书写法制备SiC纳米线气凝胶及热学性测试^[75]; (b) 冷冻法制备碳纳米管/纤维素纳米纤维水凝胶^[76]; (c) 交联增稠法打印SiO₂气凝胶及隔热应用^[77]

Figure 10. (a) process and thermal characterization of SiC nanowire aerogels by direct writing^[75]; (b) process of carbon nanotube/cellulose nanofiber mixed hydrogel by freezing method^[76]; (c) process and thermal insulation application of SiO₂ aerogels by Crosslinking thickening method^[77]

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图 11 DLP法打印了SiO₂蜂窝气凝胶^[80]

Figure 11. The DLP method printed SiO₂ honeycomb aerogels^[80]

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图 12 SLA法打印氧化石墨烯气凝胶^[81]

Figure 12. The SLA method printed graphene oxide aerogels^[81]

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图 13 模板法制备氧化石墨烯三维栅格气凝胶^[82]

Figure 13. Process of graphene oxide three-dimensional grid aerogels by template method^[82]

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图 14 有机试剂改良ZrO₂-SiO₂气凝胶^[97]

Figure 14. Process of organic reagents modify ZrO₂-SiO₂ aerogels^[97]

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图 15 不同维度碳气凝胶的性能^[98]

Figure 15. Performance of carbon aerogels in different dimensions^[98]

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图 16 钙掺杂氮化硼气凝胶的制备及阻热能力示意图^[114]

Figure 16. Process diagram and heat barrier capacity of calcium-doped boron nitride aerogels^[114]

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图 17 聚酰亚胺气凝胶的制备方法及分子链组装示意图^[122]

Figure 17. Schematic of polyimide aerogels preparation and molecular-chain assembly^[122]

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表 1 二氧化硅气凝胶物理性能

Table 1 SiO₂ aerogel physical properties

Properties	Index	Ref
Density/(kg·m⁻³)	3~500	[16]
Pore size/nm	10~150	[16]
Porosity/%	80~100	[16]
Thermal conductivity/(mW·m⁻¹·K⁻¹)	10~30	[17]
Surface area/(m²·g⁻¹)	200~1600	[18]
Temperature resistance/℃	500(m.p＞1200)	[15]
Poisson's ratio	0.2	[17]
Young's modulus/MPa	0.01~100	[16]

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表 2 不同纤维增强二氧化硅气凝胶的热-力性能

Table 2 Thermo-mechanical properties of SiO₂ aerogel after enhancement by different fiber.

Aerogel composition	Mechanical property/MPa	Thermal conductivity/ (mW·m⁻¹·K⁻¹)	Ref.
SiO₂	0.01	0.030	[16]
SiO₂/Carbon Nanotubes	0.20	0.031	[24]
SiO₂/Graphene oxide	0.65	0.018	[25]
SiO₂/cellulose nanofibril	0.12	0.023	[26]
SiO₂/Quartz fiber	1.24	0.033	[27]
SiO₂/Glass fiber	1.34	0.021	[28]
SiO₂/Zr₂O₂ fiber	0.17	0.032	[29]
SiO₂/Aramid fiber	0.14	0.022	[30]
SiO₂/Blown foam	0.31	0.012	[31]

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表 3 不同打印方式对比

Table 3 Comparison of 3D printing methods

Printing methods	Description	Characteristics
Extrusion-based printing	Preparing the ink with appropriate viscosity firstly, and form the required 3D structure layer by layer by means of nozzle extrusion.	1.Various shapes printable. 2.Low equipment cost.
Light-based printing	Using photo-curable resin to cure layer by layer to form a 3D structure by ultraviolet or visible light in the presence of a photoinitiator.	1.Usually short curing time and relatively high efficiency. 2.High printing accuracy.
3D printed templating	Using 3D printed resin as a template or mould. After injecting sol, the template is removed by dissolution or pyrolysis to form a 3D structure	1.No special requirements for sol control. 2.Suitable for traditional molecule-derived sols.

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表 4 不同类别的阻燃气凝胶性能对比

Table 4 Comparison of the performance of different types of insulating aerogel

Category	types	Advantages	Disadvantages
Inorganic aerogel	Oxidation aerogels, Nitride aerogels, Carbide aerogels.	Low density, low thermal conductivity, high porosity	Insufficient mechanical properties, deformation at high temperatures
organic aerogel	Cellulose aerogel, polyimide aerogel	Good mechanics and abundant raw materials	Poor high temperature resistance, easy aging, poor durability
organic - inorganic composite aerogel	Binary and multi-component composite aerogels, composite aerogels with substrates	Balancing mechanical properties and flame retardancy, Integrated versatility	Low porosity and high density

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长摘要

目的
由于气凝胶独特的三维纳米网络结构使其同时具有超低密度和超低热导率的特性，因而关于气凝胶的研究一直是热点领域，大量科研人员对此进行了很多研究工作，形成丰硕的研究成果。本工作通过对近些年气凝胶研究成果进行梳理总结，为其他想了解、学习气凝胶隔热前沿进展的科研人员提供借鉴，考虑到当前围绕气凝胶进展研究主要集中在功能、方法的区分，具体到隔热这一具体领域的研究较少，因此，本综述立足气凝胶的阻燃隔热应用，分析了气凝胶材料的制备方式，重点论述了溶胶-凝胶法、分子路线法、静电纺丝法、3D打印等方法并对气凝胶材料在隔热领域的应用进行了总结；后续又对气凝胶的材料选用等方面进行探讨，最后展望和分析气凝胶的未来研究重点方向。
方法
本研究围绕气凝胶的阻燃隔热主题，采取定量分析和定性论述相结合的办法。由于气凝胶的隔热阻燃性能与气凝胶的结构和组成密切相关，而结构与制备方法存在直接联系，因而，从气凝胶的制备方法和材料2个方面论述了气凝胶在隔热阻燃方面的应用，并通过Citespace文献计量工具，利用分析关键词整理了气凝胶的隔热阻燃用的发展趋势和动向，进而总结了不同方法和材料的优缺点，最后展望了气凝胶未来研究重点。
结果
纵然阻燃隔热用气凝胶制备方法和制备材料多种多样，但均存在缺点不足，达到商业化的成熟应用仍需进一步努力。在制备方法方面，溶胶-凝胶制备路线虽然技术简单且路径成熟，但气凝胶制备材料受限，且制备的气凝胶骨架结构仅通过纳米粒子相互连接，脆性大且易塌陷，需要增强工艺提升力学性能；纳米构筑单元组装法扩大了凝胶种类，优化了凝胶性能，实现对凝胶功能精准调控，但也是需要增强气凝胶力学性能；其他制备方法，诸如3D打印、静电纺丝等方式，存在加工效率低、制备成本高等缺点，需进一步优化制备设备、改进接收装置。在制备材料方面，包括无机气凝胶、有机气凝胶和通过多组分材料制备的无机/有机复合气凝胶3类，无机气凝胶虽然阻燃性好，但力学性需要改进提升；有机气凝胶与之相反，力学性能优异但高温易燃分解；进而提出无机/有机复合气凝胶制备路线，有效兼顾了力学-耐高温性能，但性能也需要进一步提升。
结论
纵然气凝胶在阻燃隔热领域的研究取得了突破和发展，但距离产业化和商业化的应用仍存在差距，未来还需要开展更多工作。在此，本文提出关于阻燃隔热用气凝胶建设建议：一是进一步加强机理研究。探讨气凝胶的合成方法、孔隙形成机制、内部结构与其热-机械能之间的联系，为更好制备高性能气凝胶提供理论指导；二是开发新型纳米结构。当前，通过纳米构筑气凝胶的基础单元多为均匀结构，关于多孔结构或其它新型结构研究较少；且构筑单元的形貌、大小对气凝胶多孔结构的影响进而如何作用于阻燃隔热的研究较少；三是建立气凝胶阻燃评价体系。气凝胶阻燃隔热性能评价主要通过灼烧样品后观察结构完整性判断其性能。然而对其他性能，诸如力学性能、体积变化等无过多测试；四是研制集成多功能气凝胶。现代工业高速发展对材料的综合性能提出越来越高的要求，单一卓越性能的材料已难以满足市场需要，要充分利用气凝胶隔热阻燃性能的天然属性，开展交叉研究，研制多功能气凝胶，扩展在不同领域的应用性。诸如在建筑行业，开发透光隔热气凝胶，能够较普通玻璃减少50％以上的供暖能耗，降低光照强度；在纺织行业，针对高原寒区官兵对冬服御寒、抗菌、轻便的特殊需求，气凝胶纤维能够屏蔽人体热辐射、降低服装30％重量，另外赋予其抗菌功能，提升卫生性，更好保障高原官兵。五是如何精准控制气凝胶的孔洞结构、开发气凝胶双网络体系、研究快捷高效的干燥方法等将成为未来研究重点，对此大量的研究者也在积极探索，在制备方法、干燥方式以及材料研制上不断有新进展，以此提升气凝胶的综合性能和实现低成本简单的制备。我们相信，随着研究的不断深入，气凝胶将会推动现有领域的发展并可能创造新功能。