Hydrogen-Bond Regulation Mechanism of the Interfacial Dilational Modulus in Sorbitol-Alkylamine Surfactants and Their Applications in Green Foams

The interfacial arrangement of surfactant molecules dictates the properties of adsorption films, rendering the molecular adsorption mechanisms fundamentally critical. This study integrates interfacial dilational rheology with molecular dynamics simulation to unravel the adsorption mechanism of renewable sorbitol-alkylamine surfactant (SAAS-C₁₂) at air/water (A/W) and n-decane/water (D/W) interfaces. We report the first discovery that hydrogen-bond switching governs the precise modulation of interfacial film strength: at the A/W interface, the transition from intramolecular hydrogen-bonded rings (low-concentration, irreversible adsorption) to intermolecular hydrogen-bonded networks (high-concentration, reversible adsorption) drives a distinctive bimodal dilational modulus trend while confining relaxation processes to slow molecular rearrangement. At the D/W interface, n-decane molecules weaken the interaction between surfactant alkyl chains by competing with surfactant molecules via van der Waals forces, converting the high-concentration modulus maximum to a gradual-decay plateau and concurrently redirecting dominant relaxation toward rapid diffusion exchange. Clarifying the mechanism of the interfacial dilational modulus dominated by hydrogen bonds helps to design green surfactants with good foam performance, showing promise for sustainable applications in the food industry, pharmaceutical delivery, and enhanced oil recovery.