Abstract
An experimental study is conducted on the interfacial fracture of an adhesively bonded polyampholyte (PA) hydrogel fabricated with anionic sodium p-styrenesulfonate (NaSS) and cationic 2-acryloyloxyethyltrimethylammonium chloride (DAC), P(NaSS-co-DAC). This study employs a novel specimen configuration combined with the J-integral method to evaluate fracture behavior under both mode-I and mixed-mode loading. The interfacial fracture toughness of ionically bonded P(DAC-co-NaSS) hydrogels made of varying NaSS: DAC molar ratios (0.9:1.1, 1:1, 1.1:0.9, and 1.5:0.5) are determined and found that increasing anionic monomer contents led to significantly higher fracture toughness, with the 1.5:0.5 ratio exhibiting the highest 12 J/m & sup2;, a 1.7-fold increase over the lowest, 4.5 J/m & sup2; for 0.9:1.1 ratio. Additionally, the influence of sodium chloride (NaCl) on the interfacial ionic bonding is explored using P(NaSS-co-DAC) of a 1:1 NaSS: DAC molar ratio. NaCl-treated interface exhibited significantly enhanced interfacial strength, resulting in a maximum 100% increase in fracture toughness compared to that without the NaCl treatment. Lastly, the fracture toughness of all P(NaSS-co-DAC) PA and NaCl-treated hydrogels is demonstrated to be higher fracture toughness under mixed-mode loading, compared to mode-I conditions. Digital Image Correlation (DIC) is employed to map the strain distribution at the crack tip and to explain determined fracture toughness values.