Concentration dependence of mechanical properties of polyacrylamide near the sol-gel transition point

The scaling law derived from the percolation theory was applied to the concentration dependence of mechanical properties of polyacrylamide measured near the sol–gel transition point. The critical concentration of the sol–gel transition, ϕ_g, was estimated from the plot of concentration (ϕ) vs. the reciprocal of viscosity (η) by extrapolating 1/η to zero. The critical exponent for the sol viscosity, s, which was estimated from the slope of the log(ϕ_g–ϕ) vs. log η plot was about 0.7. The estimated value of s was similar to the value predicted by the percolation theory based on the superconductor–normal conductor mixture model. The critical exponent for the gel elasticity, t, as estimated from the slope of the log(ϕ–ϕ_g) vs. log G′ plot, where G′ was the dynamic shear modulus of the gel at a frequency of 2Hz. The value of t was about 2, which was also similar to the value predicted by the percolation theory. These results indicated the at the concentration dependences of η and G′ of polyacrylamide near the sol–gel transition point were described by the percolation theory.