The structure of water adsorbed in polymers

Typescript (photocopy).Water adsorbed in polymers is important for mechanical, electrical, and other physical properties. At low concentrations the water does not freeze but becomes immobile at about 150(DEGREES)K. Polymers have many small channels and interstices where there is not enough room to form three-dimensional ice crystals. Water remains mobile in these channels far below 273(DEGREES)K but it is more restricted than in the bulk state; therefore, it has different properties. Clusters of water molecules, hydrogen bonded together, should exhibit cooperative motion. Our research is directed at elucidating the nature of this "nonfreezable" water by using dielectric spectroscopy and differential scanning calorimetry. Since water is dielectrically active its mobility can be studied as a function of temperature, frequency, salt concentration, and water content in an alternating electric field. Results show a wide distribution of relaxation times for the water molecules; this can be explained by assuming many different cluster sizes for the water molecules each with its characteristic relaxation time. As the temperature is lowered the molecules of water become sluggish and finally stop moving; this can be seen as constant value of the dielectric loss after 150(DEGREES)K. Our studies have concentrated on methylcellulose but a review of the literature indicated the properties of the water are almost independent of the polymer host. ..