Copper Nanoparticle Synthesis in Compressed Liquid and Supercritical Fluid Reverse Micelle Systems

Abstract

Synthesis of copper nanoparticles within sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles was performed by implementing compressed liquid and supercritical fluid (SCF) alkanes as the bulk solvent of the microemulsion system. In this reverse micelle reaction media, the role of the anionic surfactant AOT is twofold. Initially, the AOT creates a thermodynamically stable microemulsion system consisting of water and metal ions encased within an AOT surfactant reverse micelle and dispersed within a bulk oil phase. The AOT surfactant also acts as a stabilizing ligand where the surfactant tails sterically stabilize the synthesized copper particles in solution. Our previous experimental and modeling studies have shown that the strength of the solvent interactions between the bulk liquid organic solvent and the surfactant tails affects the particle growth rate and the mean copper nanoparticle size synthesized within the microemulsion system. The thermophysical properties of compressed liquids and SCFs can be tuned through adjustments in temperature and pressure. This affords the unique ability to control particle synthesis within the reverse micelle systems by adjusting the strength of the interaction between the surfactant tails and the bulk solvent. Our results demonstrate that an increase in pressure or a decrease in temperature results in the ability to synthesize slightly larger particles. In compressed propane, the median particle diameter synthesized can be shifted from 5.4 to 9.0 nm with an increase in pressure from 241 to 345 bar. Synthesis in compressed and SCF ethane is achieved at a pressure of 517 bar and can be slightly adjusted with temperature and even more so with the addition of a liquid alkane cosolvent. A soft-sphere modeling approach was taken to model the total interaction energy of copper particles, stabilized by AOT surfactant and dispersed within the bulk fluid, and effectively support our experimental results.

Recent advances in nanoparticle synthesis with reversed micelles

“…In w/o microemulsions, the most popular choice of surfactant is AOT and for most liquid/supercritical alkanes, AOT can still be applied. 62,138,144 However, when using liquid or supercritical CO 2 , AOT will not form stable microemulsions alone, being of low compatibility with the continuous CO 2 phase (discussed in chapters 3 and 7). Fluorinated co-surfactants, such as PFPE-PO 4 (perfluoropolyether-phosphate) [141][142][143]147 or F-pentanol 139,148 must be employed to stabilize the dispersions.…”

Final Report for Fractionation and Separation of Polydisperse Nanoparticles into Distinct Monodisperse Fractions Using CO2 Expanded Liquids

“…Previously, studies have been done to predict the particle size that can be stabilized at given conditions in conventional liquid solvents 23 , supercritical ethane 24 , compressed propane 25 and supercritical CO 2 26 . Shah et al 24 initiated this soft sphere modeling approach, where stabilization of nanoparticles in a given solvent depends on the balance between the van der Waals attractive forces with steric repulsive forces.…”

“…There is experimental evidence that thiol tails on a metal surface are in the extended mode. For example, using IR spectroscopic and ellipsometric data, Porter et al 39 have shown that thiol tails with hydrocarbon group (-CH 2 ) greater than 9 assemble on gold surfaces in a densely packed manner with fully extended alkyl chains tilted from the surface normal by [20][21][22][23][24][25][26][27][28][29][30] o . This suggests that the Condensed Phase Model may not be the correct phenomenological model for our experimental system.…”

Continuous Tuning of Cadmium Sulfide and Zinc Sulfide Nanoparticle Size in a Water‐in‐Supercritical Carbon Dioxide Microemulsion

“…Above that pressure, the average size of the silver nanoparticles remained virtually constant with smaller standard deviations. Synthesis of copper nanoparticles in reverse micelles was performed by Kitchens and Roberts [18] using compressed liquid and supercritical fluid alkanes as the bulk solvent. The size of the nanocrystals was found to increase with pressure.…”

“…Tuning of CdS nanoparticles by density variation appears to work well at short reaction times where the exchange-channel mechanism and the micellar-templating effect dominate. For very long reaction times, as the nanoparticles grow larger, the surfactant might act as a dispersant ligand [18] and www.chemeurj.org sterically stabilizes the nanoparticles without involving the microemulsion. Conversely, in the case of ZnS nanoparticles, the reaction time seems not to affect the final particle size.…”