The role of responsive branched copolymer composition in controlling pH-triggered aggregation of “engineered” emulsion droplets: towards selective droplet assembly‡

Stable polymer-functionalized oil-in-water emulsion droplets are prepared with precise surface compositions, which are defined by that of the branched copolymer surfactant. The influence of composition, specifically ratios of methacrylic acid (MA) to ethylene glycol (EG), on acid-triggered inter-polymer/inter-droplet hydrogen-bonding events is studied. It is demonstrated that simple variation of the EG : MA ratio can: (i) control the kinetics of, and thereby switch “on and off”, inter-droplet interactions, and (ii) control the stiffness and mechanical integrity of aggregated “engineered emulsions” under shear. We exemplify these points by demonstrating selective acid-triggered assembly of binary mixtures of contra-functionalized emulsion droplets. It is postulated that these results will allow fine-tuning of complex assembled engineered emulsion systems with the principles developed being applicable to other disperse systems (i.e., colloids and nanoparticles) and surfaces (i.e., for reversible adhesion).