Evolution of microstructure in mixed niobia-hybrid silica thin films from sol-gel precursors

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:404

Article

Besselink, Rogier¹  Stawski, Tomasz M.¹  Castricum, Hessel. L.²  ten Elshof, Johan E.¹ 

[1] Univ Twente, MESA Inst Nanotechnol, NL-7500 AE Enschede, Netherlands

[2] Univ Amsterdam, Van t Hoff Inst Mol Sci, NL-1018 WV Amsterdam, Netherlands

关键词: Niobia;    SAXS;    Phase separation;    In situ film drying;    Organosilica;    Silsesquioxane;    Correlation peak;   

DOI  :  10.1016/j.jcis.2013.04.031

来源: Elsevier

【 摘 要 】

The evolution of structure in sol-gel derived mixed bridged silsesquioxane-niobium alkoxide sols and drying thin films was monitored in situ by small-angle X-ray scattering. Since sal-gel condensation of metal alkoxides proceeds much faster than that of silicon alkoxides, the incorporation of d-block metal dopants into silica typically leads to formation of densely packed nano-sized metal oxide clusters that we refer as metal oxide building blocks in a silica-based matrix. SAXS was used to study the process of niobia building block formation while drying the sol as a thin film at 40-80 degrees C. The SAXS curves of mixed niobia-hybrid silica sols were dominated by the electron density contrast between sol particles and surrounding solvent. As the solvent evaporated and the sol particles approached each other, a correlation peak emerged. Since TEM microscopy revealed the absence of mesopores, the correlation peak was caused by a heterogeneous system of electron-rich regions and electron poor regions. The regions were assigned to small clusters that are rich in niobium and which are dispersed in a matrix that mainly consisted of hybrid silica. The correlation peak was associated with the typical distances between the electron dense clusters and corresponded with distances in real space of 1-3 nm. A relationship between the prehydrolysis time of the silica precursor and the size of the niobia building blocks was observed. When 1,2-bis(triethoxysilyl)ethane was first hydrolyzed for 30 min before adding niobium penta-ethoxide, the niobia building blocks reached a radius of 0.4 nm. Simultaneous hydrolysis of the two precursors resulted in somewhat larger average building block radii of 0.5-0.6 nm. This study shows that acid-catalyzed sol-gel polymerization of mixed hybrid silica niobium alkoxides can be rationalized and optimized by monitoring the structural evolution using time-resolved SAXS. (C) 2013 Elsevier Inc. All rights reserved.

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