Self organization in oleic acid-coated CoFe2O4 colloids: a SAXS study

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.Facultad de Ciencias ExactasInstituto de Física La Plat

Assessing written work by determining competence to achieve the module-specific learning outcomes.

This chapter describes lasers and other sources of coherent light that operate in a wide wavelength range. First, the general principles for the generation of coherent continuous-wave and pulsed radiation are treated including the interaction of radiation with matter, the properties of optical resonators and their modes as well as such processes as Q-switching and mode-locking. The general introduction is followed by sections on numerous types of lasers, the emphasis being on todayʼs most important sources of coherent light, in particular on solid-state lasers and several types of gas lasers. An important part of the chapter is devoted to the generation of coherent radiation by nonlinear processes with optical parametric oscillators, difference- and sum-frequency generation, and high-order harmonics. Radiation in the extended ultraviolet (EUV) and x-ray ranges can be generated by free electron lasers (FEL) and advanced x-ray sources. Ultrahigh light intensities up to 1021 W/cm2 open the door to studies of relativistic laser–matter interaction and laser particle acceleration. The chapter closes with a section on laser stabilization