Heterografted Molecular Brushes as Stabilizers for Water-in-Oil Emulsions

A series of well-defined heterografted molecular brushes with poly(ethylene oxide) (PEO) and poly(n-butyl acrylate) (PBA) side chains were synthesized via atom transfer radical polymerization (ATRP). Structural parameters including graft length, graft ratio, and backbone length were systematically tuned by using a synthetic strategy combining grafting through and grafting from methods. Coexistence of hydrophilic and hydrophobic grafts allowed these molecular brushes to stabilize water-in-oil emulsions at extremely low surfactant concentration (0.005 wt %). The effects of graft length and composition were demonstrated by tunable performance/behavior in the generation of emulsions. A comparison between molecular brushes of different conformation and their diblock analogues indicated that combining multiple hydrophilic and hydrophobic grafts in one molecule could enhance their adsorption at the interface but did not necessarily favor the formation of smaller droplets. The lowering of interfacial tension in pendant drop experiments provided evidence that the emulsifying properties of heterografted molecular brushes could be partially attributed to a decrease in the energy cost of emulsion formation.