Reconsideration of the results of the two dimensional correlation infrared spectroscopic study on water diffusion process in poly(ɛ-caprolactone) matrix

Two dimensional correlation spectroscopy (2DCOS) is a powerful technique which can enhance spectral resolution and probe a certain sequential order of spectral variations under external perturbation. However, in asynchronous 2D contour maps which provide richer valuable information than synchronous ones, some effects other than real asynchronicity (called spectral effects), such as position shift, band width change and band overlapping, may generate interfering cross peaks. In this paper, we performed a simulation in the region of OH stretching vibration of water to evaluate the contributions of spectral effects on a highly overlapped band and study the dynamic changes of water during diffusion process in poly(ɛ-caprolactone) (PCL) matrix. From the comparison between experimental and simulated asynchronous 2D correlation spectra, the detailed information on water diffusion process in PCL film can be extracted. It is demonstrated that artificial asynchronous cross peaks in the region of 3670–3570 cm−1 are induced by band overlapping and the bound and free water in PCL matrix change simultaneously.