Effect of Adsorbed Amphiphilic Copolymers on the Interfacial Activity of Superparamagnetic Nanoclusters and the Emulsification of Oil in Water

Abstract

A series of sub-100 nm superparamagnetic iron oxide nanoparticles with amphiphilic poly(acrylic acid-b-butylacrylate); PAA-b-PBA) copolymer shells were synthesized and characterized by NMR spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and a superconducting quantum interference device (SQUID) to investigate the effect of the polymer structure on the interfacial tension for nanoparticles adsorbed at the dodecane-water interface. Large reductions in interfacial tension of up to 27.6 mN/m were measured at nanoparticle concentrations of 0.27 wt %, indicating significant nanoparticle adsorption and interaction between the oil and water molecules at the interface. The adsorption energy of the polymer-coated nanoparticles at the dodecane/water interface was determined from the interfacial tension and nanoparticle radius, and analyzed in terms of the structure of the polymer stabilizer. Furthermore, the equilibrium adsorption of amphiphilic copolymer-functionalized iron oxide nanoclusters at the oil–water interface was determined by material balance from the concentration in the excess water phase and the known overall oil/water interfacial area. The formation and stabilization of oil droplets were on the order of 10 μm in water with unusually low nanoparticle concentrations was explained in terms of the high interfacial activity of the particles.