Abstract
The phase transition behaviour of water—polyelectrolyte systems containing polymers such as sodium carboxymethyl cellulose, xanthan and alginic acids, and having water contents ( W c) ranging from 0 to 4.0 (g water/g dry polymer), was investigated by differential scanning calorimetry (DSC). When such systems were quenched from the isotropic liquid state to 150K and then heated to 350K, four kinds of phase transition [glass transition ( T g), cold crystallization ( T cc), melting ( T m) and liquid crystal transition ( T *)] were observed on DSC heating curves. T g decreased with increasing W c and showed a minimum temperature when freezable water was present; T g then increased with increasing W c. This suggests that the main chain motion of polyelectrolytes associated with non-freezing water is restricted by the existence of freezable water in the system. At a temperature higher than T m a liquid crystalline phase is formed, since mobile freezable water induces the molecular alignment of the polyelectrolytes and their associated non-freezing water.
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