Neutron Diffraction of Ice in Hydrogels.

Neutrondiffraction patterns for deuterated poly-N,N,-dimethylacrylamide (PDMAA) hydrogels were measuredfrom 10 to 300 K to investigate the structure and properties of waterin the gels. Diffraction peaks observed below 250 K indicate the existenceof ice in the hydrogels. Some diffraction peaks from the ice are atlower diffraction angles than those in ordinary hexagonal ice (Ih).These shifts in peaks indicate that the lattice constants of the aand caxes in the ice are about 0.29and 0.3% higher than those in ice Ih, respectively. The results showthat bulk low-density ice can exist in PDMAA hydrogels. The distortionsin the lattice structure of ice imply significant interactions betweenwater molecules and the surrounding polymer chains, which play animportant role in the chemical and mechanical properties of the hydrogel. [ABSTRACT FROM AUTHOR]