Phase transitions and phase separations in aqueous polyether systems

Detailed investigations on the structural and macroscopic properties of a hydrogel based on a polyether/water/LiCl system as a function of composition and temperature are reported. The investigations include the determination of the types of water by differential scanning calorimetry (DSC) measurements, the characterization of the polymorphism by microscopic observations in combination with DSC measurements as well as the determination of the optical and viscoelastic properties by spectroscopic and rheological measurements. The influence of the addition of salts on the water binding properties of the polyether are reported and the results are discussed on a molecular level. For the optical properties it was found that the transmission–temperature curves reflect the polymorphism of the samples. Two-phase regions at a phase transition or regions of coexisting phases (phase separation or mixing gaps) lead to the appearance of light scattering states, whereas homogeneous phase regions are highly transparent. The rheological measurements indicate the formation of hydrogels by cross-linking with LiCl, whereby in different phases the gelation occurs at different LiCl concentration ranges. Received: 3 August 2000 Revised: 19 November 2000 Accepted: 29 November 2000