In situ photon transmission experiments were performed using UV-visible (UVV) spectrometer during the drying of polyacrylamide (PAAm) gels. These gels are formed from acrylamide (AAm) with various N,N' -methylenebis(acrylamide) (Bis) contents by free radical crosslinking copolymerization (FCC) in water. The transmitted light intensity, I-sc increased continuously as PAAm gels are dried. Increase in I,, was attributed to the decrease in the scattered light intensity, I-sc, which might be originated from the contrast between "frozen blob clusters" and holes in the drying gel. Decrease in I-sc was modeled using Rayleigh's equation, where drying times with various exponents were found to be proportional to the volume of frozen blob clusters. It was observed that the radius of frozen blob cluster (correlation length), xi (c) increased in various power of time, depending on Bis contents during drying of gels. (C) 2001 John Wiley & Sons, Inc.