Fourier transform infra-red spectroscopic studies of water molecules sorbed in solid polymers

Water structures in polymeric matrices were studied using Fourier transform infra-red (FTi.r.) spectroscopy. The infra-red spectra of water sorbed in many polymers imply systematic changes. As the polymer becomes more hydrophilic, among the three bands corresponding to the normal vibrational modes of an isolated water molecule the va(OH) and vs(OH) bands gradually shift to lower frequencies, while the δ(< HOH) band moves to a higher frequency. Using these shifts, we have deduced the heat of water sorption for several hydrophobic polymers. Moreover, it has been found that the atom with the largest electronegativity in the polymers increases the bending frequency shift, Δδ(< HOH), more than the stretching frequency shifts, Δva(OH) and Δvs(OH). Eventually, it was concluded that water molecules sorbed in solid polymers, in almost all cases (for both hydrophilic and hydrophobic materials), form either strong or weak hydrogen bonds with particular site atoms in the polymers. Various water structures in these polymeric matrices were discussed in terms of the FTi.r. data that were obtained.