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In this study, a self-healing hydrogel was prepared that is transparent to visible (Vis) light while absorbing ultraviolet (UV), infrared (IR), and microwave. The optothermal features of the hydrogel were explored by monitoring temperature using an IR thermometer under an IR source. The hydrogel was synthesized using sodium tetraborate decahydrate (borax) and polyvinyl alcohol (PVA) as raw materials based on a facile thermal route. More significantly, graphene oxide (GO) and graphite-like carbon nitride (g-C3N4) nanostructures as well as carbon microsphere (CMS) were applied as guests to more dissect their influence on the microwave and optical characteristics. The morphology of the fillers was evaluated using field emission scanning electron microscopy (FE-SEM). Fourier transform infrared (FTIR) attested that the chemical functional groups of the hydrogel have been formed and the result of diffuse reflection spectroscopy (DRS) confirmed that the hydrogel absorbs UV while is transparent in Vis light. The achieved result implied that the hydrogel acts as an essential IR absorber due to its functional groups desirable for energy efficiency and harvesting. Interestingly, the achieved results have testified that the self-healing hydrogels had the proper self-healing efficiency and self-healing time. Eventually, microwave absorbing properties and shielding efficiency of the hydrogel, hydrogel/GO, g-C3N4, or CMS were investigated, demonstrating the salient microwave characteristics, originated from the established ionic conductive networks and dipole polarizations. The efficient bandwidth of the hydrogel was as wide as 3.5 GHz with a thickness of 0.65 mm meanwhile its maximum reflection loss was 75.10 dB at 14.50 GHz with 4.55 mm in thickness. Particularly, the hydrogel illustrated total shielding efficiency (SET) > 10 dB from 1.19 to 18 and > 20 dB from 4.37 to 18 GHz with 10.00 mm in thickness. The results open new windows toward improving the shielding and energy efficiency using practical ways.

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A series of crosslinked copolymers with cationic nature have been prepared based on acrylamide (AAm) and [3-(methacryloylamino)propyl]trimethyl ammonium chloride (MAPTAC) using N,N methylene-bis-acrylamide (MBA) as crosslinking agent. Taguchi's method has been employed for the purpose of formulation design and optimization as well as investigating the effects of various compositional parameters, such as total monomer concentration, cationic monomer and crosslinking agent concentration. The swelling behaviour of the synthesized gels in electrolyte solutions composed of ions with different valency has been studied and compared with an anionic-based superabsorbent. The swelling capacity and absorbency were found to be enhanced with increase of the MAPTAC moieties of the copolymer chains, and therefore increase of their cationic character. All the cationic hydrogels prepared had greater swelling capacity, with less change in their swelling behaviour, when immersed into aqueous solutions containing multivalent cations. The anionic-based hydrogels collapsed in similar ionic solutions with moderate-to-high ionic strength and did not show any tendency to re-swell. The complex modulus (G * ) of the crosslinked copolymers in the equilibrium swollen state was measured by rheomechanical spectroscopy and was correlated with the chemical composition of the network. Thermogravimetric analysis of the dry cationic superabsorbent showed more bound water but similar thermal behaviour to crosslinked polyacrylamide 