Wide frequency rheological modeling of crosslinked polyacrylamide gels

Gels are known to behave as viscoelastic materials but only a small amount of data is usually provided in the glassy transition. Results concerning the dynamic moduli G′ and G′′ are presented here using AFM in contact oscillatory mode and show good agreement with classical rheological data. Different gels are studied with increasing polymer concentration. G0N, the plateau modulus, is measured at low frequencies, but interestingly another one, G1, is found at high frequencies. A model based on fractional derivatives is proposed, covering the whole frequency range. The relaxation spectrum is recovered, and the physical parameters contain interesting information about the local dynamics of crosslinks.