Glycerol/NaCl-Regulated Poly(vinyl alcohol)/Sodium Alginate/Graphene Oxide Composite Gels with Low-Temperature Flexibility and a Strain-Dependent Resistance Response

Flexible gel sensors can lose mechanical compliance and electrical stability at low temperature or during solvent loss. A poly(vinyl alcohol) (PVA)/sodium alginate (SA)/graphene oxide (GO) composite gel was prepared by freeze–thaw cycling and post-treated in either aqueous NaCl or a NaCl-containing water/glycerol mixture (1:2, v/v). The water/glycerol–NaCl-treated gel (F-G/S/P/G) exhibited a maximum tensile stress of 428 ± 27 kPa and an elongation at break of 432 ± 27% at room temperature (n = 3), and remained visibly deformable after 24 h at −20 °C. During ambient storage, it retained approximately 89% of its initial mass after 35 days. The cycle-averaged peak ΔR/R0 increased from 0.135 at 20% strain to 1.142 at 250% strain, and the 20–60% linear region gave a gauge factor of 1.01 (R2 = 0.9988). Three independently prepared sensing elements gave a peak ΔR/R0 of 0.710 ± 0.019 at 100% strain, with response and recovery times of 1.22 ± 0.07 and 1.04 ± 0.06 s, respectively. After 500 cycles at 100% strain, the normalized peak response retained 95.1% of its initial value. Overall, F-G/S/P/G combined low-temperature deformability, ambient-storage mass retention, and repeatable resistance sensing.