Molecular Relaxation of Cellulosic Polyelectrolytes with Water

Abstract

The molecular relaxation of the liquid crystalline state of the water-cellulosic polyelectrolyte system was investigated using nuclear magnetic resonance spectroscopy (NMR) and differential scanning calorimetry (DSC). DSC and polarizing light microscopic observation showed that the system forms the liquid crystalline state, when the water content (Wc) of the system ranges from 0.5 to 2.5 (Wc = grams of water/gram of dry sample) depending on the type of polyelectrolyte. The water-polyelectrolyte system forms a homogeneous mixture and has a regular molecular alignment. The temperature and the enthalpy of transition from the liquid crystalline state to the isotropic liquid state decreased with increasing Wc. The longitudinal relaxation time (T1) and transverse relaxation time (T2) of 1H and 23Na of a water-Na cellulose sulfate system were measured as functions of temperature and Wc in the range where the liquid crystalline state was formed. The 1H T2 value gradually decreased with decreasing temperature and showed a sudden decrease in the temperature range where the mobile fraction of water molecules in the system froze. The 23Na T2slow value showed a sudden decrease at the temperature where the liquid crystalline state was formed. NMR and DSC results suggested that the Na ion is associated with the main chain in the liquid crystalline state, and the increase of free and freezing bound water surrounding hydrophilic groups hinders the regular molecular alignment of polyelectrolyte molecules through the dissociation between the Na ion and the main chain.