Hydrogels have emerged as viable materials for diverse applications owing to their responsiveness; the effects of swelling and dehydration on their mechanical properties have been widely studied. Fourier-transform infrared spectroscopy and X-ray diffraction analyses elucidated the structure of poly(vinyl alcohol) (PVA) following freeze–thaw (F–T) cycles and ethanol (EtOH) immersion. However, the reswelling capacity of hydrogels after dehydration and their EtOH stimulus responsiveness remain unexplored. In this study, we examined the responsiveness and toughness of PVA/polyacrylamide (PAM) double-network (DN) hydrogels through single-cycle loading–unloading tests. Tensile strength and strain energy increased with F–T cycling, whereas the mechanical properties of the PVA/PAM DN hydrogels after EtOH immersion depended on the immersion medium. Although the strain energy of PVA DN hydrogels increased due to PVA crystallization during EtOH immersion after F–T cycles, it decreased in distilled water (DW) to levels comparable to hydrogels without EtOH immersion. Therefore, the mechanical properties of PVA/PAM DN hydrogels were gradually enhanced by EtOH immersion and subsequently reversed by reswelling in DW. It is expected that the volume-changing functionality of these hydrogels can be applied as novel EtOH sensors. • Ethanol responsiveness of PVA/PAM double-network hydrogels was examined • Freeze–thaw cycled hydrogels were tensile tested in ethanol/distilled water • Mechanical properties improved with increasing freeze–thaw cycles • Mechanical properties enhanced with increasing ethanol concentration • Ethanol immersion effects reversed upon reswelling in distilled water
Yoshida et al. (Fri,) studied this question.