Self organization in oleic acid-coated CoFe2O4 colloids: a SAXS study
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We report a structural study of magnetic colloids composed of CoFe2O4 nanoparticles (mean radii in the range 2–7 nm) synthesized by thermal decomposition of different high boiling temperature organic solvents in the presence of oleic acid and oleylamine, and subsequently re-suspended in hexane. Although the surfactant layer prevents permanent aggregation and precipitation of the disperse phase, competition between attractive interactions (i.e., dipolar and van der Waals) and repulsive steric interaction leads to self organization of the magnetic nanoparticles. Our small angle X-ray scattering results evidence the presence of distinctive self organized structures in the liquid colloid depending on the type of solvent used in the synthesis. A completely homogeneous dispersion is obtained for those colloids synthesized with benzyl-ether and octadecene. Bi-disperse systems, in which nanoclusters coexist with free nanoparticles, appear when phenyl-ether and trioctylamine are used. Chain-like structures are observed in a colloid containing the particles synthesized using phenyl-ether, while more compact 3D structures form in colloids prepared with particles synthesized with trioctylamine. The presented results have important implications in the design and selection of magnetic nanoparticles for those applications where the size dispersion determines the final efficiency of the material, such as magnetic fluid hyperthermia clinical therapy.
KeywordsMagnetic colloids Aggregation Dipolar interaction London–van der Waals interaction Small angle X-ray scattering
We thank financial support from: LNLS synchrotron, Campinas, SP, Brazil under proposals D11A-SAXS1-9293, CONICET (PIP 01111) and ANPCyT (PICT 00898) of Argentina and the Spanish Ministerio de Ciencia e Innovación (projects MAT2010-19326 and CONSOLIDER NANOBIOMED CS-27 2006). Valuable help of Dr. A. Ibarra on TEM analysis and Dr. Aldo Craievich on SAXS data analysis is deeply acknowledged.
- Evans W, Prasher R, Fish J, Meakin P, Phelan P, Keblinski P (2008) Effect of aggregation and interfacial thermal resistance on thermal conductivity of nanocomposites and colloidal nanofluids. Int J Heat Mass Transfer 51(5–6):1431–1438. doi: 10.1016/j.ijheatmasstransfer.2007.10.017 CrossRefGoogle Scholar
- Gonzalez-Fernandez MA, Torres TE, Andrs-Vergs M, Costo R, de la Presa P, Serna CJ, Morales MP, Marquina C, Ibarra MR, Goya GF (2009) Magnetic nanoparticles for power absorption: Optimizing size, shape and magnetic properties. J Solid State Chem 182(10):2779–2784. doi: 10.1016/j.jssc.2009.07.047 CrossRefGoogle Scholar
- Kim BH, Lee N, Kim H, An K, Park YI, Choi Y, Shin K, Lee Y, Kwon SG, Na HB, Park JG, Ahn TY, Kim YW, Moon WK, Choi SH, Hyeon T (2011) Large-scale synthesis of uniform and extremely small-sized iron oxide nanoparticles for high-resolution t1 magnetic resonance imaging contrast agents. J Am Chem Soc 133(32):12624–12631. doi: 10.1021/ja203340 CrossRefGoogle Scholar
- Kruglyakov PM (2000) Chapter 2 Stabilising ability of surfactants in emulsification and foam formation. In: Kruglyakov PM (ed) Hydrophile-Lipophile balance of surfactants and solid particles physicochemical aspects and applications, studies in interface science, vol 9, Elsevier, pp 100–145, doi: 10.1016/S1383-7303(00)80015-0
- Kwak K, Kim C (2005) Viscosity and thermal conductivity of copper oxide nanofluid dispersed in ethylene glycol. Rheology 17(2):35–40Google Scholar
- Rosensweig RE (1997) Ferrohydrodynamics. Dover books on physics. Dover Publications, New York. http://books.google.com.ar/books?id=uSa5nJGXYicC
- Weinstein JS, Varallyay CG, Dosa E, Gahramanov S, Hamilton B, Rooney WD, Muldoon LL, Neuwelt EA (2010) Superparamagnetic iron oxide nanoparticles: diagnostic magnetic resonance imaging and potential therapeutic applications in neurooncology and central nervous system inflammatory pathologies, a review. J Cereb Blood Flow Metab 30(1):15–35. doi: 10.1038/jcbfm.2009.192 CrossRefGoogle Scholar