NMR of dissolved water in ultrathin and thick membranes of cellulose acetate

Abstract

AbstractWide‐line proton magnetic resonance spectra of thick (100 μ) and ultrathin (0.25 μ) membranes of cellulose acetate have been obtained in the “bone‐dry” state and in the wet state up to 2.5% water by weight. The NMR spectra were recorded with the membrane face aligned parallel and perpendicular to the magnetic field direction. The first derivative spectra of wet thick membrane (above 0.4% water) show a sharp center peak and at least one broad outer peak, both in the parallel and perpendicular orientations. The spectra of wet ultrathin membrane, on the other hand, show a pseudodoublet in the perpendicular orientation and a broad singlet in the parallel orientation. The differences in the spectra of the thick and ultrathin membranes are discussed in terms of “free” and restricted water believed to arise from the differences in the structure of thick and ultrathin membranes.