National Synchrotron Radiation Research Center, Hsinchu Science Park, Hsinchu 30076, Taiwan; Department of Chemistry and Center of Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan.
National Synchrotron Radiation Research Center, Hsinchu Science Park, Hsinchu 30076, Taiwan.
J Colloid Interface Sci. 2021 Feb 15;584:647-659. doi: 10.1016/j.jcis.2020.10.114. Epub 2020 Nov 4.
Multistage silicate self-organization into light-weight, high-strength, hierarchically patterned diatom frustules carries hints for innovative silica-based nanomaterials. With sodium silicate in a biomimetic sol-gel system templated by a tri-surfactant system of hexadecyltrimethylammonium bromide, sodium dodecylsulfate, and poly(oxyethylene-b-oxypropylene-b-oxyethylene) (P123), mesoporous silica nanochannel plates with perpendicular channel orientation are synthesized. The formation process, analogous to that of diatom frustules, is postulated to be directed by an oriented self-assembly of the block copolymer micelles shelled with charged catanionic surfactants upon silication.
The postulated formation process for the oriented silica nanochannel plates was investigated using time-resolved small-angle X-ray and neutron scattering (SAXS/SANS) and freeze fracture replication transmission electron microscopy (FFR-TEM).
With fine-tuned molar ratios of the anionic, cationic, and nonionic surfactants, the catanionic combination and the nonionic copolymer form charged, prolate ternary micelles in aqueous solutions, which further develop into prototype monolayered micellar plates. The prolate shape and maximized surfactant adsorption of the complex micelles, revealed from combined SAXS/SANS analysis, are of critical importance in the subsequent micellar self-assembly upon silicate deposition. Time-resolved SAXS and FFR-TEM indicate that the silicate complex micelles coalesce laterally into the prototype micellar nanoplates, which further fuse with one another into large sheets of monolayered silicate micelles of in-plane lamellar packing. Upon silica polymerization, the in-plane lamellar packing of the micelles further transforms to 2D hexagonal packing of vertically oriented silicate channels. The unveiled structural features and their evolution not only elucidate the previously unresolved self-assembly process of through-thickness silica nanochannels but also open a new line of research mimicking free-standing frustules of diatoms.
多阶段硅酸盐的自组织形成轻量、高强度、具有层次图案的硅藻壳，为创新的基于二氧化硅的纳米材料提供了线索。在十六烷基三甲基溴化铵、十二烷基硫酸钠和聚（氧乙烯-氧丙烯-氧乙烯）（P123）的三表面活性剂体系模板的仿生溶胶-凝胶体系中，使用硅酸钠合成具有垂直通道取向的介孔二氧化硅纳米通道板。该形成过程类似于硅藻壳的形成过程，据推测是由带电荷的两性离子表面活性剂壳层的嵌段共聚物胶束在硅化过程中的定向自组装所引导的。
使用时间分辨小角 X 射线和中子散射（SAXS/SANS）以及冷冻断裂复制透射电子显微镜（FFR-TEM）研究了定向二氧化硅纳米通道板的假定形成过程。
通过精细调整阴离子、阳离子和非离子表面活性剂的摩尔比，两性离子组合和非离子共聚物在水溶液中形成带电荷的、拉长的三元胶束，进一步发展成原型单层胶束板。从联合 SAXS/SANS 分析中揭示的拉长形状和最大的表面活性剂吸附对于硅酸盐沉积后随后的胶束自组装至关重要。时间分辨的 SAXS 和 FFR-TEM 表明，硅酸盐复合胶束侧向聚合并融合成单层硅酸盐胶束的大薄片，在平面层状堆积中。在二氧化硅聚合后，胶束的面内层状堆积进一步转化为垂直取向的二氧化硅通道的 2D 六方堆积。揭示的结构特征及其演变不仅阐明了以前未解决的贯穿厚度二氧化硅纳米通道的自组装过程，而且为模仿自由站立的硅藻壳开辟了一条新的研究路线。
