Photon transmission technique for monitoring swelling of acrylamide gels formed with various crosslinker contents

Photon transmission experiments were performed using a UV–visible (UVV) spectrometer during the swelling of polyacrylamide (PAAm) gels. These gels were prepared from acrylamide (AAm) with various N,N′-methylenebisacrylamide (Bis) contents by free-radical crosslinking copolymerization (FCC) in water and dried before use for swelling experiments. Transmitted light intensity, Itr increased at very early times when PAAm gels are immersed in water, then decreased continuously as swelling time is increased. Decrease in Itr was attributed to the increase in the scattered light intensity, Isc which may originate from the contrast between ‘frozen blob clusters’ and holes in the swelling gel. Decrease in Itr was modelled using the Li–Tanaka equation from which time constants, τ1, and collective diffusion coefficients, Do were determined for various Bis content PAAm gels. τ1 and Do were found to be strongly correlated with the wavelength, λ, of Itr and the Bis content of the gel samples. The correlation between λ and τ1 and Do predicts the existence of ‘frozen blob clusters’ in PAAm gels.