Mechanical testing of hydrogels and PAN gel fibers

Uniaxial and biaxial mechanical tester was developed to perform basic tests for characterization of soft, low strength polymer gels. We have considered stress/strain relationship of acrylamide-based and polyacrylonitrile (PAN) fiber and sheet gels. Acrylamide-based gels (neutral, anionic, cationic, amphoteric) were tested uniaxially, where Young's modulus estimated varies between 10 and 25 kPa. Uniaxial and biaxial tension tests were performed on PAN sheets, from which Young's modulus was estimated at 6.65MPa, which is an extraordinarily large strength than the conventionally investigated acrylamide-based gels. Its length change in response to EtOH/H2O solution exchange proved to be not small as an actuator material, and it was observed that PAN exhibited a deformation in response to the electric field. Two types of PAN gel fibers were tested as a bundle of 50 fibers. True stress-strain data were obtained showing similar non-linear trend in both cases. Statistical methods were used to assess fiber strength distribution.