COMPRESSIONAL MODULUS OF SWOLLEN POLYACRYLAMIDE NETWORKS

For a set of nominally identical polyacrylamide-water gel samples an experimental comparison is made between the values of MOS, the longitudinal osmotic modulus observed by quasi-elastic light scattering, the osmotic modulus KOS, observed by swelling pressure measurements, and the shear modulus G, measured by mechanical deformation. From theoretical considerations it is shown that in inhomogeneous gels KOS+4/3G$GRMOS. The difference observed experimentally is, however, larger than expected from the heteroeneity of these gels and is attributed to the calibration method used in the light-scattering technique. The present results can thus be used as a calibration for the latter method. All the results are consistent with good solvent scaling predictions, which apply for the osmotic deswelling measurements, up to concentrations of 0.25 g cm-3. Moreover, the osmotic Poisson ratio adopts a value 0.275±0.011, in agreement with that expected for fully swollen gels in a good solvent, namely, 0.278.