PREPARATION OF HOMOGENOUS OCTANOIC ACID COATED 𝜸-Fe2O3 NANOPARTICLE MONOLAYERS USING A MIXED SOLVENT SYSTEM
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2016-06-06
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Abstract
While magnetic nanoparticles have many exciting potential applications, one common obstacle that needs to be overcome is their instability in air and solution. We investigated a less common surfactant, octanoic acid, to coat and stabilize iron oxide magnetic nanoparticles. Highly crystalline and monodisperse octanoic acid coated 𝛾-Fe2O3 magnetic nanoparticles were synthesized by the thermal decomposition of iron(0) pentacarbonyl. The presence of octanoic acid capped iron oxide nanoparticles was confirmed by FT-IR spectrum. With a coordination separation less than 110 cm-1, nanoparticles formed a bidentate coordination between carboxylate and the iron oxide metal surface. The product nanoparticles were controlled in size and shape with an average diameter of 2.8 ± 0.7 nm.
Previous studies used a single, nonpolar, solvent to disperse octanoic acid coated iron oxide nanoparticles, which resulted in the formation of aggregates. Different ratios of chloroform and methanol (5:1 to 1:5 by volume) were used as dispersing agents for the nanoparticles in order to determine if a mixed solvent system would prevent nanoparticle aggregation by creating a significantly larger solvent sphere that would further stabilize these nanoparticles in solution.
By using the Langmuir-Blodgett (LB) technique, compressed monolayers of nanoparticles at the air-water interface were prepared. The monolayers were then transferred onto Transmission Electron Microscopy (TEM) grids using either the LB or Langmuir-Schaefer (LS) methods. Two other thin film preparation methods: drop casting and spin coating were also used for monolayer formation comparison. TEM images revealed that highly crystalline packing of nanoparticles could be achieved by preparing LB films using a chloroform and methanol mixture in a 4:1 ratio. The average interparticle spacing was determined to be 1.9 ± 0.4 nm. This distance was comparable with the theoretical prediction of 1.8 nm, which showed octanoic acid did not interdigitate during the packing process.
Results suggested that applying a mixed solvent system of chloroform and methanol to disperse octanoic acid coated maghemite nanoparticles could reduce aggregation of these particles in solution thus promoting more ordered nanoparticle packing.
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Nanoparticles