Vijay R. Tirumala1, Taiki Tominaga2, Eric K. Lin1, Wen-li Wu1, Hidemitsu Furukawa2, Jian Ping Gong2, and Yoshihito Osada2. (1) Polymers Division, National Institute of Standards and Technology, 100 Bureau Dr Stop 8541, Gaithersburg, MD 20899, (2) Laboratory of Soft and Wet Matter, Hokkaido University, Sapporo, Japan
Hydrogels are swollen polymer networks with more than 95% water by volume. Most hydrogels, however, are mechanically too weak to be used as load bearing devices. However, it was recently shown that the toughness of hydrogels can be increased by orders of magnitude by synthesizing hydrogels with a double network (DN) structure. In this method, a high molecular weight linear polymer is synthesized within the porous hydrogel network. Despite containing 90% water by volume, these tough gels exhibit a fracture stress (~170 kg/cm^2) similar to that of articular cartilage found in the bone-joints of human body. Here, we discuss the static structure of DN-gels and their response to an applied stress studied using neutron scattering. Quite surprisingly, we found that the suppression of network inhomogeneities is closely related to the increased toughness of DN-gels.