Visualizing chemical compositions and kinetics of sol-gel by near-infrared multispectral imaging technique.

Kinetics of sol-gel formation were studied using the recently developed near-infrared (NIR) multispectral imaging instrument. This imaging spectrometer possesses all the advantages of conventional spectrometers. It also has additional features that NIR spectrometers cannot offer, namely, its ability to provide kinetic information at different positions within a sample. The high spatial resolution and sensitivity of the InSb camera make it possible for the imaging spectrometer 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, MTES, or a mixture of these two alkoxysilanes 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 x 10) is used for calculation. The inhomogeneities observed for TEOS sol-gels are different from those for the MTES sol-gels, and those for sol-gels prepared from a mixture of TEOS and MTES are relatively larger and more similar to those of the MTES sol-gels. A variety of reasons might account for the observed inhomogeneities including differences in the structure of the TEOS sol-gels and MTES sol-gels and the inability of the TEOS to mix well with MTES with the latter being more hydrophobic.