Scaling of rheological properties of hydrogels from associating polymers

Rheological properties of thermoreversible hydrogels of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) have been studied. The relaxation exponent Delta = 0.69 is found from the frequency-independent loss tangent at the gel point. The distance from the gelation threshold (epsilon) is varied by changing the concentration or temperature. Dependencies of the zero-shear viscosity (eta(o)) and equilibrium modulus (G(o)) scale as eta(o) similar to epsilon(s) and G(o) similar to epsilon(t). The transient exponents s = 1.26-1.28 and t = 2.64-2.65 are obtained in the vicinity of the gelation threshold. The scaling relation between all exponents is in excellent agreement with the Rouse model and is consistent with the percolation theory. Transient rheological properties exhibit complex scaling behavior above the gel point depending on epsilon. Scaling above the gel point correlates with the polymer structure.