Hollow amphiphilic crosslinked nanocapsules from sacrificial silica nanoparticle templates and their application as dispersants for oil spill remediation

Abstract

Hollow amphiphilic crosslinked nanocapsules were synthesized by sequential grafting-from of crosslinked hydrophobic polycaprolactone (PCL) via ring-opening polymerization and grafting-to of hydrophilic poly(ethylene glycol) (PEG) onto 70 nm silica nanoparticles, followed by removal of the silica core. To accomplish the crosslinking of the PCL layer a bis-caprolactone monomer was used. The effects on the brush properties of PCL grafted silica nanoparticles with crosslinker were investigated. Incorporation of only 0.25 mol% crosslinker in the bulk grafting reaction resulted in dramatic effects, such as significantly enhanced brush length and high molecular weight dispersities. Hollow PCL nanocapsules were synthesized by performing the grafting reaction of PCL with 2.5 mol% crosslinker under dilute conditions. Upon removal of the silica core, a significant increase in hydrodynamic radius was observed due to the relief of constrain of surface tethered chain ends and swelling in a good solvent. PEG was then coupled to particles grafted with crosslinked PCL to yield amphiphilic block polymer grafted silica nanoparticles, which displayed excellent dispersibility in water, and resulted in a contraction of the PCL layer, as determined by dynamic light scattering. Core removal of the amphiphilic block polymer grafted silica nanoparticles gave hollow amphiphilic crosslinked nanocapsules which displayed significant swelling in good, non-selective solvent conditions, and a collapsed hydrophobic core block in aqueous conditions. Finally, the amphiphilic materials, both before and after core removal, were determined to be effective at stabilizing hydrocarbons in water, with the hollow nanocapsules having ca. 15 times greater uptake capacity.