Phase transitions and phase separations in aqueous polyether systems

Detailed investigations on the structural and macroscopic properties of a h ydrogel 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) measureme nts, the characterization of the polymorphism by microscopic observations i n combination with DSC measurements as well as the determination of the opt ical and viscoelastic properties by spectroscopic and theological measureme nts. 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-tempe rature curves reflect the polymorphism of the samples. Two-phase regions at a phase transition or regions of coexisting phases (phase separation or mi xing gaps) lead to the appearance of light scattering states, whereas homog eneous phase regions are highly transparent. The theological measurements i ndicate the formation of hydrogels by cross-linking with LiCl, whereby in d ifferent phases the gelation occurs at different LiCl concentration ranges.