Lai Wei-Chi, Hong Li-Tzuen
Department of Chemical and Materials Engineering, Tamkang University , No. 151, Yingzhuan Road, Tamsui District, New Taipei City 25137, Taiwan.
Energy and Optoelectronic Materials Research Center, Tamkang University , No. 151, Yingzhuan Road, Tamsui District, New Taipei City 25137, Taiwan.
J Phys Chem B. 2016 Sep 22;120(37):10010-7. doi: 10.1021/acs.jpcb.6b04272. Epub 2016 Sep 14.
In conventional sol-gel methods, gel formation occurs due to aggregation of particles into irregular shapes of larger size. In this study, we conducted hydrolysis-condensation reactions of tetraethyl orthosilicate (TEOS) within water-laden channels inside the space created by self-assembled AOT molecules to prepare regular and nanosized silica in self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) gels. The AOT gels were obtained by adding small amounts of water to organic solvents containing high concentrations of AOT. Adding silica significantly influenced the rheological properties and microstructures of these AOT/silica gels. Rheological studies showed that the storage modulus G' and loss modulus G″ of the AOT gel systems became very close and even crossed, indicating that the gel is "weak"; however, for the AOT/silica gel systems, the rheological data demonstrated that G' is greater than G″ at all frequencies, indicative of a real gel with a G' of approximately 10(5) pa. Small-angle X-ray scattering (SAXS) results showed that the gels initially had a hexagonal close-packed cylindrical structure with long-range order and transitioned to nonclose-packed cylindrical structures without long-range order as the silica formed. The cylinder is expected to comprise stacks of silica molecules surrounded by AOT molecules, and the radius of the cylinder is close to the sum of the length of one AOT molecule and half the size of one silica molecule. The rheological and SAXS data show that silica in the AOT/silica systems grew in the axial direction due to the confinement of these cylindrical structures, leading to nanowire silica structures. After removal of the AOT components, the nanowire silica was approximately 5-10 nm in diameter, as observed using transmission electron microscopy (TEM).
在传统的溶胶-凝胶法中，凝胶的形成是由于颗粒聚集成更大尺寸的不规则形状。在本研究中，我们在由自组装的双（2-乙基己基）磺基琥珀酸钠（AOT）分子形成的空间内充满水的通道中进行原硅酸四乙酯（TEOS）的水解缩合反应，以在自组装的AOT凝胶中制备规则且纳米尺寸的二氧化硅。通过向含有高浓度AOT的有机溶剂中加入少量水来获得AOT凝胶。添加二氧化硅显著影响了这些AOT/二氧化硅凝胶的流变学性质和微观结构。流变学研究表明，AOT凝胶体系的储能模量G'和损耗模量G''变得非常接近甚至交叉，表明该凝胶是“弱”凝胶；然而，对于AOT/二氧化硅凝胶体系，流变学数据表明在所有频率下G'都大于G''，这表明是一种真正的凝胶，其G'约为10⁵帕。小角X射线散射（SAXS）结果表明，凝胶最初具有具有长程有序的六方密堆积圆柱结构，随着二氧化硅的形成转变为没有长程有序的非密堆积圆柱结构。预计圆柱由被AOT分子包围的二氧化硅分子堆叠组成，圆柱的半径接近一个AOT分子的长度与一个二氧化硅分子大小的一半之和。流变学和SAXS数据表明，由于这些圆柱结构的限制，AOT/二氧化硅体系中的二氧化硅在轴向生长，形成纳米线二氧化硅结构。去除AOT成分后，使用透射电子显微镜（TEM）观察到纳米线二氧化硅的直径约为5-10纳米。
