Citation

Mojun Liu, Peiyi Wu*, Yifu Ding, Gang Chen, and Shanjun Li*. Two-Dimensional (2D) ATR−FTIR Spectroscopic Study on Water Diffusion in Cured Epoxy Resins. Macromolecules 2002, 35, 5500-5507.

Abstract

A novel experimental approach, based on time-resolved two-dimensional (2D) ATR−FTIR spectroscopy has been used to study water diffusion behavior of novolac epoxy resins cured with novolac resin and novolac acetate resin named as EP and EPA, respectively. The diffusion coefficients calculated by a nonlinear curve fitting are quite consistent with the results of gravimetric analysis. In 2D-IR spectra, the splitting of the water OH vibration band at 2800−3700 and 1500−1800 cm-1 shows that there are two different states of water in epoxy networks, in which one could be confined into free volume (microvoids) or molecularly dispersed with less hydrogen-bonding (bulk dissolved), while the other could be attributed to bound water forming strong hydrogen-bonding with hydrophilic groups of epoxy networks. The sequential order of intensity changes of the two water bands elucidates that, in the process of water diffusion into epoxy networks, water molecules first bind with specific hydrophilic groups as bound water and then diffuse into free volume (microvoids) or molecularly dispersed with less hydrogen-bonding (bulk dissolved). The wavenumber difference of OH vibration band appearing from bound water between EP and EPA indicates that water molecules form much stronger hydrogen-bonding with EP networks than with EPA networks.