Thermodynamic Interactions in Double-Network Hydrogels.
March 16th, 2008 | by admin |Thermodynamic Interactions in Double-Network Hydrogels.
Double-network hydrogels (DN-gels) prepared from the combination of a moderately cross-linked anionic polyelectrolyte (PE) and an uncross-linked linear polymer solution (NP) exhibit mechanical properties such as fracture toughness that are intriguingly superior to that of their individual constituents. The scheme of double-network preparation, however, is not equally successful for all polyelectrolyte/neutral polymer pairs. A successful example is the combination of poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) cross-linked network and linear polyacrylamide (PAAm), which results in DN-gels with fracture strength under compression approaching that of articular cartilage ( approximately 20 MPa). Small-angle neutron scattering was used to determine the thermodynamic interaction parameters for PAMPS and PAAm in water as a first step to elucidate the molecular origin responsible for this superior property. Measurements on PAMPS/PAAm DN-gels and their solution blend counterparts indicate that the two polymers interact favorably with each other while in water. This favorable PAMPS/PAAm interaction given by the condition chiPE-NP < chiPE-water <chiNP-water, where chi is the Flory-Huggins interaction parameter, is consistent with some of the salient features of the DN structure revealed by SANS, and it may also contribute to the ultimate mechanical properties of DN-gels.
Tominaga T, Tirumala VR, Lee S, Lin EK, Gong JP, Wu WL.
Polymers Division, National Institute of Standards and Technology, Gaithersburg Maryland, Graduate School of Sciences, Hokkaido University, Sapporo Japan, and Polymer Science and Engineering, University of Massachusetts, Amherst Massachusetts.