Stimuli‐responsive properties of double network hydrogels derived from κ‐carrageenan and poly (acrylamide)

Abstract

AbstractThe utilization of stretchable, antifreezing hydrogels is imperative when using them as electrolyte membranes and ionic conductors for flexible energy storage devices or electronic skin. However, a problem still persists in the formation of a functional hydrogel with comprehensive performance including antifreezing, temperature‐sensitive, favorable reusability, and self‐healing properties. Herein, through anionic κ‐carrageenan (κ‐CG) as the physical noncovalent crosslinking network of the hydrogel, and acrylamide (AM) as monomers forming the second network through chemical crosslinking, κ‐CG‐Li+/PAM double‐network (DM) hydrogels were obtained by one‐pot thermally initiated polymerization. The DM structure showed excellent fracture strain and strong breaking stress, and lithium ions ensure its good electrical conductivity. The transparency of the hydrogel could reach above 91.0%, and the freezing point of the resultant gel was −34.9°C, which was measured by differential scanning calorimetry at low temperature. The as‐synthesized DM gel exhibited robust tensile properties with tensile elongation of 1840% and fracture energy of 967.3 kJ/m3. The response sensitivity of the hydrogel as a wearable sensor in different environments was explored. κ‐CG‐Li+/PAM could not only respond in the large strain range of 100%–400% but also capture the change in 0.1% strain. The deformation sensitivity was GF = 1.83 at 200% compressive strain range, and the hydrogel had a pressure sensitivity of 2.71 kPa−1 over the pressure range of 0–5 kPa. In addition to the properties of ionic conductive hydrogels, the hydrogel demonstrated outstanding temperature sensitivity in the human body temperature range of 35°C–40°C or in the range of 20°C–60°C (TCR = 1.628/°C).