Dynamic Covalent Bonding and Bridging: pH-Governed Complexation of Phenylboronic Acid-Modified Alginate with Alkyl Polyglycoside for Smart Emulsification

The dynamic covalent complexation between phenylboronic acid (PBA)-functionalized polymers and diol-containing surfactants presents a powerful strategy for fabricating smart interfacial materials. This work presents a comprehensive investigation into a pH-responsive system composed of Alg-PBA and the diol-bearing surfactant alkyl polyglycoside (APG). The pH-governed formation of boronate ester (B–O) bonds between Alg-PBA and APG dictates their interaction regimes, leading to distinct behaviors in bulk solution, at the oil–water interface, and in macroscopic emulsions. At pH 3, weak hydrogen bonding dominates, while above the p K a of PBA (pH 9 and 10), strong dynamic covalent complexes form. At intermediate pH (pH 6), the interaction is in a dynamic transitional state. These molecular-level interactions directly govern tunable interfacial activity and adsorption kinetics. Crucially, a pH-dependent “bridging effect” is identified: at low APG concentrations, Alg-PBA chains connect oil droplets into a three-dimensional network, yielding gel-like emulsions stabilized by hydrogen bonds (pH 3) or robust B–O bonds (pH 6, 9 and 10). At high APG concentrations, hydrophobic interactions disrupt this network, fluidizing the emulsion. By decoupling the interplay between pH-tunable binding, polymer conformation, and surfactant concentration, this study establishes the Alg-PBA/APG complex as a versatile, stimuli-responsive emulsifier platform. This provides a design principle for creating emulsions with on-demand rheological properties and stability for applications in drug delivery, food, and cosmetics.