Investigation of inhomogeneity in chemical compositions and kinetics of sol–gel by near-infrared multispectral imaging technique

Abstract Inhomogeneity in kinetics of sol–gel formation of tetraethyl orthosilicate (TEOS) were studied using the recently developed near-infrared (NIR) multispectral imaging instrument. This imaging spectrometer possesses all advantages of conventional spectrometers. It also has additional features which NIR spectrometers cannot offer, namely, its ability to provide kinetic information at different positions within a sample. The spatial resolution and sensitivity of the imaging spectrometer made it possible to determine the kinetic from data recorded by a single pixel. Kinetics of sol–gel reactions, determined by this multispectral imaging instrument, show that the initial hydrolysis of the TEOS is relatively inhomogeneous. The inhomogeneity is dependent on the number of pixels used to calculate the spectrum for each spot. Data calculated from a single pixel provide the largest inhomogeneity. No inhomogeneity was observed when an average of a large number of pixels (e.g., 10×10) is used for calculation. A variety of reasons might account for the observed inhomogeneity including the differences in the relative concentrations of starting materials.