Temperature-regulated elasticity and multifunctionality in n-alkyl methacrylate ester-based ternary gels: optimizing adsorption and pH/temperature dual sensitivity

An attempt was made to correlate the gelation temperature with elasticity and pH/temperature dual sensitivity of n-alkyl methacrylate ester-based cationic gels. Ternary gels were prepared by free-radical crosslinking of HPMA, DMAEMA, and GMA in water at fixed monomer and crosslinker concentrations, while gel preparation temperature T_prep was varied from − 18 to 60 °C. The structure and physical properties of ternary gels were fully characterized using thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). T_prep has been shown to be an effective independent variable to adjust both macroscopic and microscopic properties of ternary gels as desired. Gelation temperature dependence of swelling and compressive elasticity was investigated. Ternary gels synthesized at 5 °C showed maximum swelling capacity. The equilibrium swelling ratio increased first slightly up to 5 °C and then decreased continuously with increasing T_prep. This trend indicated that swelling is influenced by properties of both crosslinking region and the main constituent amorphous region. In swollen state, elastic modulus of gels changed from 0.9 to 108 kPa and increased 120 times as T_prep decreased from 60 to − 18 °C. Terpolymer gels showed pH-sensitive swelling characteristic of cationic DMAEMA monomer and exhibited high swelling ratio in acidic solutions induced by electrostatic repulsion between quaternary amine groups. The swelling ratio decreased due to hydrophobic effect of the alkyls when environmental pH is higher than 7.7. Regardless of T_prep, the gels gradually contracted as swelling temperature increased from 25 to 75 °C. Flory–Huggins interaction parameter χ ranged from 0.4005 to 0.5358 and increased with the degree of intermolecular hydrophobic interactions. The effectiveness of ternary gels for removing methyl orange from aqueous solution was tested, and the results showed that the gels prepared under low-temperature conditions were promising for removing anionic dyes. The adsorption was spontaneous and found to be a multistep process with surface adsorption followed by intraparticle diffusion. This knowledge will aid the future design of n-alkyl methacrylate ester-based ternary gels as an effective adsorbent for dye removal from wastewater and pharmaceutical preparations. Graphical abstract: Aminegroup-containing ternary gels were prepared by free radical crosslinkingpolymerization of HPMA, DMAEMA and GMA at different gel preparationtemperature. [Figure not available: see fulltext.]