Spinodal Line and Critical Point of an Acrylamide Gel

We present direct evidence for the existence of the critical point in an acrylamide gel, the gel consisting of a covalently cross-linked polymer network immersed in an acetone-water mixture. We determined the spinodal line for the gel from the measurements of the scattered light intensity. The spinodal line has a maximum at $T=(10\mathrm{}\pm 1)°$C and a network volume concentration of (18±3)%. This corresponds to the critical point.