Chen Zhi, Zhao Yongliang, Zhu Xiaomin
DWI-Leibniz-Institute for Interactive Materials e.V. and Institute for Technical and Macromolecular Chemistry of RWTH Aachen University, Forckenbeckstraße 50, Aachen 52056, Germany.
State Key Laboratory of New Textile Materials and Advanced Processing Technologies, School of Materials Science and Engineering, Wuhan Textile University, Wuhan 430200, P. R. China.
ACS Appl Mater Interfaces. 2021 Mar 17;13(10):12230-12240. doi: 10.1021/acsami.1c00205. Epub 2021 Mar 3.
Due to its extraordinary properties, silica aerogel has a high potential for a number of applications; however, the state-of-the-art technique of its production involves cost-intensive supercritical drying or solvent exchange with a nonpolar solvent. Here, we report on a pure aqueous process for the preparation of silica aerogel particles as well as silica hollow nanoparticles, which is based on the self-assembly of amphiphilic silica precursor polymers, PEGylated poly(ethoxysiloxanes) (PEG-PEOS), in water and subsequent conversion under basic conditions. Addition of a hydrophobic organic liquid to the aqueous dispersions of PEG-PEOS results in the spontaneous formation of oil-in-water emulsions, which resemble the self-assembled structures of PEG-PEOS in water swollen by the organic liquid. The products of basic conversion of the emulsions are silica aerogel particles as well as hollow nanocapsules loaded with organic liquid. Remarkably, the oil phase significantly increases the porosity of the aerogel particles by acting as a porogen; meanwhile, it only decreases the silica shell thickness of the hollow nanoparticles. During freeze-drying, the aerogel particles, acting as matrix-type microcapsules, can efficiently retain the encapsulated volatile hydrophobic liquid; at the same time, the liquid is completely evaporated from the hollow particles (core-shell-type microcapsules). The encapsulation efficiency of hydrophobic liquids in the aerogel particles can reach as high as 99% after drying. The barrier property of the aerogel particles is higher with PEG-PEOS of lower PEGylation degrees due to bigger particle size and higher meso- and microporosity. This work opens a new avenue to prepare particulate silica aerogel for different promising applications including microencapsulation.
由于其非凡的性能，二氧化硅气凝胶在许多应用中具有很高的潜力；然而，其生产的现有技术涉及成本高昂的超临界干燥或与非极性溶剂进行溶剂交换。在此，我们报道了一种制备二氧化硅气凝胶颗粒以及二氧化硅空心纳米颗粒的纯水工艺，该工艺基于两亲性二氧化硅前驱体聚合物聚乙二醇化聚（乙氧基硅氧烷）（PEG-PEOS）在水中的自组装以及随后在碱性条件下的转化。向PEG-PEOS的水分散体中添加疏水性有机液体导致自发形成水包油乳液，其类似于在被有机液体溶胀的水中PEG-PEOS的自组装结构。乳液碱性转化的产物是二氧化硅气凝胶颗粒以及负载有机液体的空心纳米胶囊。值得注意的是，油相作为致孔剂显著增加了气凝胶颗粒的孔隙率；同时，它仅减小了空心纳米颗粒的二氧化硅壳厚度。在冷冻干燥过程中，作为基质型微胶囊的气凝胶颗粒能够有效地保留封装的挥发性疏水性液体；同时，液体从空心颗粒（核壳型微胶囊）中完全蒸发。干燥后，疏水性液体在气凝胶颗粒中的封装效率可高达99%。由于粒径较大以及中孔和微孔率较高，较低聚乙二醇化度的PEG-PEOS制备的气凝胶颗粒具有更高的阻隔性能。这项工作为制备用于包括微胶囊化在内的不同有前景应用的颗粒状二氧化硅气凝胶开辟了一条新途径。
