EXPRESS: Fourier Transform Infrared (FT-IR) Imaging Analysis of Interactions Between Polypropylene Grafted with Maleic Anhydride (MAPP) and Silica Spheres (SS) Using Two-Trace Two-Dimensional (2T2D) Correlation Mapping:

A technique for analyzing IR imaging data based on two-trace two-dimensional (2T2D) correlation analysis is presented to extract pertinent information underlying spectroscopic imaging data. In 2T2D correlation mapping, each spectrum in hyperspectral data is individually compared with a reference spectrum to generate 2T2D asynchronous correlation intensity at the x- and y-coordinates on a 2T2D correlation map. Asynchronous correlation intensity develops only when the signal contribution from a certain species becomes even more significant in the sample spectrum compared with the reference spectrum. This feature can be advantageously utilized to examine molecular interaction or an intermediate form of the component present in a system of interest. 2T2D correlation mapping is examined using Fourier transform infrared (FT-IR) imaging data of polymer composites based on polypropylene grafted with maleic anhydride (MAPP) melt-mixed with silica spheres (SS). IR images derived by using conventional visualization based on a single wavenumber (i.e. 1713 cmâ1) are dominated with the overwhelming IR absorbance induced by the normal MAPP species, making the identification of subtle but pertinent changes in the composite system difficult. A 2T2D correlation map derived from the MAPP/SS composite developed a significant asynchronous correlation intensity between the IR bands at 1695 and 1713 cm-1 around a specific region on the map where the MAPP and SS coexist. On the other hand, such a correlation pattern becomes less acute when the SS is modified with the octadecyldimethyl group to prevent the hydrogen bonding with the MAPP. It thus revealed that the silanol groups on the surface of the SS substantially interact with the MAPP via the development of the hydrogen bonding.