Osmotic properties of polyelectrolyte hydrogels in physiological salt solutions

Corrcspondence/Reprint request: Dr. Ferenc Horkay, Ph.D .. Section oo Tissue Biophysics and Biomimetics, National Institutes of Health, Bldg. 13, Room 3WJ6B, 13 South Drive, Bethcsda, MD 20892, USA.E-mail:[email protected] Abstract The effect of cations on the osmotic properties of chemically cross-linked sodium polyacrylate hydrogels has been investigated. The variation of the osmotic swelling pressure, shear modulus and mixing pressure is measured when Na+ ions are substituted by different monovalent and multivalent cations. The occu"ence of a reversible volume transition induced by monovalent/divalent cation exchange is discussed. A hierarchy is established in the interaction strength according to the chemical group to which the ions belong. It is shown that a Flory-Huggins type expression provides a satisfactory description of the effect of divalent cations on the osmotic behavior of polyacrylate hydrogels both below and in the vicinity of the volume transition. Analysis of the osmotic data indicates a sharp increase in the third-order interaction parameter upon introduction of divalent cations while the second order interaction parameter