Microrheology of the liquid-solid transition during gelation.

The viscoelastic properties of physical and chemical polymer gels are characterized through the liquid-solid transition using particle tracking microrheology. Measurements of the probe particle mean-squared displacement are shifted as the extent of gelation increases to generate master curves. From the shift factors, we determine the gel point and critical scaling exponents. Both systems exhibit a critical relaxation exponent n approximately 0.6, where G' approximately G'' approximately omega n for the incipient gel, consistent with the Rouse model of dynamic scaling in the percolation universality class.