The interfacial behavior of water-soluble
poly[oligo(ethylene oxide)
monomethyl ether methacrylate], grafted from 15-nm-diameter silica
nanoparticles using a living atom-transfer radical polymerization
technique, was examined for hexane and water interfaces. The polymer-grafted
nanoparticles reduced the hexane–water interfacial tension
from ∼50 to ∼20 mN/m at concentrations of silica in
the range of 1–10 ppm. The hydrodynamic size of the dispersed
hybrid nanoparticle, a function of the molecular weight of the polymer
and grafting density, was the dominant variable in determining the
critical particle concentration and efficacy of the hybrid nanoparticles
in reducing the hexane–water interfacial tension. A simple
phenomenological model is used to explain the strong dependence of
the critical particle concentration on the effective hydrodynamic
size of the nanoparticles. Water–hexane and water–squalene
emulsions formed using 1000 ppm of hybrid nanoparticles were stable
for more than 60 days
