Journal of Colloid and Interface Science, August 1977 [antikvár]

Nature of Water in Synthetic Hydrogels III. Dilatometry, Specific Conductivity, ond Dielectric Relaxation of Poly(2,3-dihydroxypropyl methacrylote) SUNHEE CHOI and MU SHIK JHON' Department of Chemical Science, Korea Advanced Institute of Science, Seoul, Korea AND JOSEPH D. ANDRADE University of Utah, Department of Materials Science and Engineering, Salt Lake City, Utah 84112 Received August 14, 1975; accepted August 26, 1976 The hj-pothesis that three classes of water exist in hydrogels, namely, X water (bulk water-like), Z water (bound water-like) and Y water (intermediate water), has been verified, and the dj'namic aspects of those waters have been studied in poly(2,3-dihydroxj'propyl methacrylate) (PDHPMA) hydrogels. Bulk gel conductivity data for PDHPMA gel was obtained. The activation energy for specific conduction was obtained from the specific conductivity curve at various temperatures. A plot of the activation energy vs volume percent of water in the gels clearly indicated three different zones, showing three classes of water in the gels. These results were confirmed by thermal expansion measurements. The high-water-content gels (60%) showed an extremely sharp volume change at 0°C, indicating the presence of normal bulk water. Lower-water-content gels (20%) showed no anomalous change in thermal e.xpansion, indicating that the water is bound. The medium-water-content gels exhibited intermediate behavior. A semiquantitative analysis of the three classes of water is presented. The third method used was dielectric relaxation. At low frequencies the dielectric constant of PDHPMA gels is much higher than that of water. The dielectric constant decreases continuously as the frequency increases, tending to level off at about 10' Hz. The higher the concentration of polymer in the gel, the lower the dielectric constant. Results are most reasonably explained by assuming the more structured phase of water for the low dielectric constant. INTRODUCTION poljTiiers have been widely reviewed recently The nature of water has long been of great by Molyneux (4). interest and has been extensively studied. Hydrogels are promising materials for bio- Questions of water structure, water of hydra- applications (5). Many of the physical, tion, and similar problems are of biological physiological, and mterfacial properties of such significance, e.g., the structure of water in ^e related to the organization of living cells, the role of hydrated water around '^e surface of the hydro- protein molecules, etc. (1-3). There has also t^e study of the nature of water been great interest in the hydration of macro- ^y^^hetic hydrogels is very important both molecular species and the state of water for pure scientific interest and for the develop- molecules in hydrophilic polymer systems, "lent of biomedical materials. The interactions between water and synthetic substantial evidence that a fraction of water in hydrogels may be significantly > To whom correspondence should be addressed. different from normal or bulk water. Jhon and Copyright © 1977 by Academic Press, Inc. Journal of Colloid and Interface Science, Vol. 61, No. 1. August 1977 All rights of reproduction in any form reserved. ISSN 0021-9797