纳米多孔二氧化硅薄膜的制备及性能

Fabrication and characterization of nanoporous silica film

以N(C_8H_(15))_4^+OH^-为催化剂,用正硅酸乙脂(TEOS)溶胶-凝胶工艺制备出纳米多孔二氧化硅薄膜。体系的H_2O/TEOS>25,强碱催化使二氧化硅的溶解度增大并使二氧化硅胶粒带负电荷,抑制了二氧化硅的聚合。丙三醇与TEOS的水解中间体Si(OC_2H_5)_4-x(OH)_x及二氧化硅胶粒Si_xO_y(OH)_z^(+n)表面Si-OH形成氢键,抑制了二氧化硅的聚沉。聚乙烯醇(PVA)使粒状二氧化硅溶胶具有网状结构,易于成膜。薄膜由致密结构转化为均匀纳米多孔结构是构成薄膜的二氧化硅胶粒在热处理时聚集和塑性形变的结果。多孔二氧化硅薄膜的折射率为1.27～1.42,介电常数为1.578～2.016,热导率为0.2W/(m·K)。

Crack-free homogeneous nanoporous silica films were prepared with colloidal silica sol derived by sol-gel process of tetraethylorthosilicate (TEOS) catalyzed with R4N+OH-. The solution with ratio of H2O/TEOS>25, R4N+ and glycerol were combined with the intermediate Si(OR)4-x;(OH)x and SixOy(OH)z+nr avoiding aggregation of the nanosilica particles, presence of the poly(vinyl alcohol) (PVA) made colloidal silica sol a polymeric structure (filming easily). The silica films have heterostructure, which can avoid crack of the nanoporous silica films during being annealed. The homogeneous nanoporous silica films can develop due to accumulated structure of silica particle within films during annealing. The pore sizes distribute between 100-200 nm after annealed at 850 ℃ for 30 min. The refractive indexes were 1.27-1.42, the dielectric constant was 1.4-2, the thermal conductivity was 0.2 W/m.K.