Koganti Venkat R, Rankin Stephen E
Chemical and Materials Engineering Department, University of Kentucky, Lexington, Kentucky 40506-0046, USA.
J Phys Chem B. 2005 Mar 3;109(8):3279-83. doi: 10.1021/jp045037a.
Thin silica films with orthogonally aligned hexagonal close-packed cylindrical structure are synthesized by dip coating silica precursors and poly(ethylene oxide)-polyproplyene oxide (PEO-PPO) triblock surfactants (P123) onto modified glass slides. All films cast from this sol display 2D hexagonal pore structures (a approximately 6.2 nm) under transmission electron microscopy (TEM). However, X-ray diffraction (XRD) shows that confining freshly deposited films between two chemically neutral modified slides completely aligns the pores toward the direction orthogonal to the substrate. Equally effective alignment is obtained by using slides modified with either a random PEO-PPO copolymer or P123 itself. The channels in films cast onto unmodified slides, onto modified slides which are exposed to air, or onto modified slides which are exposed to unmodified glass slides align at least partially parallel to the substrate. Parallel mesophase alignment is also observed in a control experiment with a sol containing the nonionic surfactant template decaethelyne glycol hexadecyl ether (Brij-56) sandwiched between copolymer-modified slides because the surfaces are not chemically neutral toward Brij-56. This study confirms that it is possible to use substrate surface chemistry to control the orientation of mesophases in mixtures of reactive silicates and low molecular weight nonionic surfactant templates.
通过将二氧化硅前驱体和聚环氧乙烷 - 聚环氧丙烷（PEO - PPO）三嵌段表面活性剂（P123）浸涂到改性载玻片上，合成了具有正交排列的六方密堆积圆柱结构的二氧化硅薄膜。从这种溶胶浇铸的所有薄膜在透射电子显微镜（TEM）下均显示二维六方孔结构（a约为6.2 nm）。然而，X射线衍射（XRD）表明，将新沉积的薄膜限制在两个化学中性的改性载玻片之间会使孔完全沿与基材正交的方向排列。使用用无规PEO - PPO共聚物或P123本身改性的载玻片可获得同样有效的排列。浇铸在未改性载玻片上、暴露于空气中的改性载玻片上或暴露于未改性载玻片的改性载玻片上的薄膜中的通道至少部分与基材平行排列。在一个对照实验中也观察到平行介相排列，该实验中含有非离子表面活性剂模板十乙烯二醇十六烷基醚（Brij - 56）的溶胶夹在共聚物改性的载玻片之间，因为这些表面对Brij - 56不是化学中性的。这项研究证实，可以利用基材表面化学来控制反应性硅酸盐和低分子量非离子表面活性剂模板混合物中介相的取向。
