Structure–rheology–thermal property correlation in graphene oxide reinforced gum acacia-g-poly(acrylic acid) nanocomposite hydrogels

Abstract

The rational design of sustainable hydrogel systems with tailored mechanical stability and tunable viscoelastic properties remains a central challenge in soft materials science. This study addresses this challenge through systematic investigation of the rheological behaviour and microstructural characteristics of graphene oxide (GO)–reinforced gum acacia-grafted-poly(acrylic acid) (GA-g-PAA) nanocomposite hydrogels. The GA-g-PAA/GO hydrogels were synthesized via free-radical graft copolymerization using ammonium persulfate as the initiator and N,N′-methylenebisacrylamide as the crosslinker, yielding a covalently crosslinked three-dimensional network. Field-emission scanning electron microscopy reveals a pronounced morphological transition from a loosely packed, heterogeneous structure in the pristine polymer network to a dense, interconnected porous architecture upon GO incorporation, confirming uniform nanofiller dispersion and its role as a structural modulator. Rheological characterization demonstrates pronounced non-Newtonian shear-thinning behaviour across all compositions, with apparent viscosity decreasing from approximately 10³–10⁴ Pa s under low shear rates to less than 10 Pa s at 100 s⁻¹. Oscillatory strain and frequency sweep analyses establish elastic-dominant viscoelastic behaviour, as evidenced by storage modulus (G′) values consistently exceeding loss modulus (G″) across the measured frequency range. Notably, at an optimal GO loading (GO-3), G′ exhibits a more than two-fold enhancement, increasing from ∼59 Pa for the pristine hydrogel to ∼131 Pa, indicating a substantial reinforcement of network stiffness. Thermogravimetric analysis further confirms improved thermal stability, reflected in elevated degradation temperatures and increased char yields reaching approximately 26% in GO-reinforced formulations. These property enhancements are attributed to the multifunctional role of GO nanosheets, which act as effective physical crosslinkers, establish strong interfacial interactions with the polymer matrix, restrict segmental mobility, and facilitate efficient stress transfer within the hydrogel network. Collectively, these findings establish controlled GO incorporation as a decisive parameter for engineering the structural integrity, viscoelastic response, and thermal endurance of gum acacia-based hydrogels. The resulting GA-g-PAA/GO nanocomposite hydrogels present a promising platform for advanced applications, including adsorption technologies, injectable and self-healing biomaterials, soft actuators, and stimuli-responsive smart hydrogel systems.