Abstract: Pattern formation in polymeric hydrogel associated with volume phase transition was observed in strong gel shrinking. Chemically cross linked poly(sodium acrylate/acrylamide) gel was prepared and shaped by capillary. The gel cylinder was suddenly dipped into acetone or into an acid aqueous solution. The former exhibited bamboo-like pattern, similar to the report in the literature. But a novel pattern, gel helix or gel spring, was found in the latter case. Macroscopic patterns only occurred in a strong gel collapse, and nothing was found in a step by step volume shrinking. The helix is with period between 0.1 to 1 mm and formed within 100 second. Both right hand sense and left hand sense could be obtained. Once formed, the gel helix cannot be recovered by re swelling in basic solution. Surface crack and its helical growth were observed and could account for the formation of gel helix preliminarily.

Key words: Polymeric hydrogel, Volume phase transition, Pattern formation, Helix