Partitioning Behavior
of Silica-Coated Nanoparticles
in Aqueous Micellar Two-Phase Systems: Evidence for an Adsorption-Driven
Mechanism from QCM‑D and ATR-FTIR Measurements
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Abstract
Quartz crystal microbalance with dissipation (QCM-D),
attenuated
total reflectance Fourier transform infrared spectroscopy (ATR-FTIR),
and total organic carbon detection (TOC) are employed to examine the
cause of the differences in the partitioning of silica-coated nanoparticles
in an aqueous micellar two-phase system based on nonionic surfactant
Eumulgin ES. The particles partition into the micelle-rich phase at
pH 3 and into the micelle-poor phase at pH 7. Our results clearly
show that the nonionic surfactants are adsorbed to the silica surface
at pH 3. Above the critical temperature, a stable surfactant bilayer
forms on the silica surface. At pH 7, the surfactants do not adsorb
to the particle surface; a surfactant-loaded particle is therefore
drawn to the micelle-rich phase but otherwise repelled from it. These
results suggest that the partitioning in aqueous micellar two-phase
systems is mainly driven by hydrogen bonds formed between the surfactants
and the component to be partitioned