Aluminum nanoparticles capped by polymerization of alkyl-substituted epoxides: ratio-dependent stability and particle size.

We report here on the polymerization of epoxide monomers on incipient aluminum nanoparticle cores and the effects of changing the epoxide-capping precursor and the metallic monomer ratio on the resultant stability and particle size of passivated and capped aluminum nanoparticles. When altering the ratio of aluminum to cap monomer precursor, nanoparticles capped with epoxydodecane, epoxyhexane, and epoxyisobutane show a clear decreasing trend in stability with decreasing alkane substituent length. The nanoparticle core size was unaffected by cap ratio or composition. PXRD (powder X-ray diffraction) and DSC/TGA (differential scanning calorimetry/thermal gravimetric analysis) confirm the presence of successfully passivated face-centered cubic (fcc) aluminum nanoparticles. We also report preliminary results from ATR-FTIR (attenuated total reflectance-Fourier transform infrared), (13)C CPMAS (cross-polarization/magic-angle spinning), and (27)Al MAS solid-state NMR (nuclear magnetic resonance) measurements. The most stable aluminum nanoparticle-polyether core-shell nanoparticles are found at an Al:monomer mole ratio of 10:1 with an active Al(0) content of 94%.

Capping and passivation of aluminum nanoparticles using alkyl-substituted epoxides.

We report here on the synthesis and passivation of small (20-30 nm) aluminum nanoparticles using alkyl-substituted epoxides as capping agents. FTIR and 13C NMR spectroscopy indicate that the epoxides polymerize to form a polyether cap on the surfaces of the aluminum nanoparticles. Nanoparticles capped with epoxyhexane and epoxydodecane are stable in air, but particles capped with epoxyisobutane are pyrophoric. TEM images show spherical Al particles. Powder X-ray diffraction shows the presence of crystalline Al. Titrimetric analysis of the core-shell nanostructures in air reveals that 96% of the total aluminum present is active (unoxidized) aluminum.