Formation of Nanofibrous Structure in Biopolymer Aerogel during Supercritical CO2 Processing: The Case of Chitosan Aerogel
Formation of Nanofibrous Structure in Biopolymer Aerogel during Supercritical CO2 Processing: The Case of Chitosan Aerogel
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DOI：
10.1021/acs.biomac.9b00246
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发表时间：
2019-05-01
影响因子：
6.2
通讯作者：
Yoda, Satoshi
中科院分区：
文献类型：
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作者：
Takeshita, Satoru;Sadeghpour, Amin;Yoda, Satoshi
超临界干燥被广泛认为是生产保持凝胶微观结构的气凝胶的黄金标准，但我们发现情况并非总是如此。壳聚糖气凝胶是一种新兴的生物高分子气凝胶，通过化学交联凝胶化，然后与甲醇进行溶剂交换和使用CO2进行超临界干燥来制备。小角X射线散射分析表明，由单个分子链的高斯链组成的湿凝胶结构在CO2处理过程中转化为纳米纤维网络。原位观察揭示了在CO2中凝胶的急剧收缩，表明壳聚糖和CO2之间的低亲和力引起的物理凝聚是主要的结构形成步骤。这些结果挑战了对超临界干燥的普遍看法：它不再是一种非活性干燥方法，而是一种活性纳米结构，形成了一种生产具有定制结构和性能的多孔生物聚合物材料的工具。
Supercritical drying is widely considered as the gold standard to produce aerogels that preserve the microstructure of the gels, but we have found this is not always the case. Chitosan aerogel, one of the emerging biopolymer aerogels, was prepared by chemical cross-linking gelation, followed by solvent exchange with methanol and supercritical drying using CO2. Small-angle X-ray scattering analysis shows that the structure of the wet gel, which consists of Gaussian chains of individual molecular strands, converts into a nanofibrous network during CO2 processing. In situ observation reveals a drastic shrinkage of the gel in CO2 demonstrating that physical coagulation caused by the low affinity between chitosan and CO2 is the main structure-forming step. These results challenge the common perception of supercritical drying: it is no longer an inactive drying method, but rather an active nanostructure forming a tool to produce porous biopolymer materials with tailored structure and properties.