Ultra-Long-Chain Biobased Nonionic Surfactants with Cryo-Tolerance and Viscoelasticity

Conventional glycol- and glycerol-based antifreezes effectively depress freezing points but lack the viscoelastic properties required for non-Newtonian fluid applications under subzero conditions. To overcome this limitation, a series of nonionic ultralong-chain alkenyl gluconamide surfactants (UCAGS) were synthesized from renewable rapeseed-derived monounsaturated fatty acids (UC18–UC24) and hydroxyl-rich N-Methyl-d-glucamine or N-Ethyl-d-glucamine. The molecular architecture integrates a polyhydroxyl headgroup with an ultralong hydrophobic tail, enabling a balance between solubility and self-assembly. These biobased surfactants significantly reduce the freezing temperature of water, with the UC22GEt variant reaching −14.5 °C at 5 wt %. This performance corresponds to a 2.5-, 2.9-, and 9.1-fold greater depression compared to 10 wt % ethylene glycol (EG), propylene glycol (PG), and glycerol (GLY), respectively. Simultaneously, they transform aqueous systems from Newtonian to non-Newtonian fluids, imparting pronounced shear-thinning behavior and enhanced viscosity at below-zero temperatures. Mechanistic studies indicate that the hydrogen bonding between hydroxyl-rich headgroups and water suppresses ice formation, while self-assembly into lamellar liquid crystalline structures restricts ice crystal growth and modulates rheology. Biodegradability assessments confirm the environmental compatibility of the materials. These developed UCAGS thus represent dual-functional cryoprotective fluids that independently regulate both freezing point and flow behavior, offering a sustainable alternative to petroleum-derived antifreezes.