Salt-tolerant and self-healing hydrogel containing cationic hyperbranched poly (amido amine) as electrostatic and chemical cross-linking junctions

The excellent salt tolerance of ionic electrostatic and chemical double cross-linking hydrogels (D-IEC gel) was demonstrated using cationic hyperbranched poly(amido amine) as both electrostatic and chemical cross-linking junctions in an electrolyte solution. The D-IEC gel can be synthesized in NaCl concentrations ranging from 0 to 4.5 mol/L, while the single ionic electrostatic cross-linking hydrogel containing linear cationic monomers (SL-IEC gel) cannot form when the salt concentration exceeds 0.6 mol/L. Notably, the elastic modulus (G’) of the D-IEC gel, formed in a 4.5 mol/L NaCl solution, decreased slightly from 28.00 kPa (in distilled water) to 24.01 kPa––yielding a G’ retention rate of 85.75%, which is nearly 27 times higher than that of conventional IEC gels. Additionally, the D-IEC gel exhibited a self-healing efficiency of up to 90%. From practical applications, the G’ values of the D-IEC gel synthesized in a 3.5 wt% NaCl aqueous solution (similar to seawater) and in distilled water were measured, revealing a retention rate of 87.61%, significantly outperforming conventional IEC gel (3.18%). These findings indicate that the D-IEC gel, with its salt tolerance and self-healing capabilities, is a promising candidate for industrial materials, even in highly concentrated electrolyte solutions. Their exceptional performance is attributed to the structural stability of the hyperbranched polymer in an electrolyte solution and the dynamic irreversibility of ionic electrostatic cross-linking owing to the high charge density of the hyperbranched units.