Neutron diffraction study of hydrogels

Sekine, Yurina   ; Fukazawa, Tomoko*; Kobayashi, Riki*; Chi, S.*; Fernandez, J.*; Fukazawa, Hiroshi

Hydrogels are unique materials that can contain a large amount of water in their three-dimensional polymer chain networks. We used neutron diffraction to probe the structure of DO in poly-,,-dimethylacrylamide (PDMAA) hydrogel. Two PDMAA hydrogels with high and low DO-content W (W = 0.9 and 0.5) were prepared. The neutron diffraction measurements were performed using the Wide Angle Neutron Diffractometer (WAND) at the High Flux Isotope Reactor in Oak Ridge, U.S.A. The samples were rapidly cooled using liquid nitrogen, and then heated from 10 to 300 K. The neutron diffraction profiles of the high DO-content PDMAA gel (W = 0.9) have strong sharp peaks below 270 K that are similar to diffraction patterns of hexagonal ice Ih. At 300 K, the profile has a broad liquid-like diffraction feature. The profile of the gel at W = 0.5 has a broad band in the 2 range from 20 - 28 below 230 K that are similar to diffraction pattern of glassy water. Sharp peaks are observed in the profile at 230 K. The feature of the profile is similar to that of cubic ice. The profile at 260 K has ice Ih-like strong peaks. Our neutron diffraction results show the existence of ice in hydrogels and that the structure of ice depends on the water content of the hydrogel. The structural changes of ice in hydrogels might have important implications in the interpretation of hydrogel properties, for both biological tissues and synthetic gel materials.