Workshop on magnetic fluids

Em processament

Lyotropic ferronematic liquid crystals based on new Ni, Cu and Zn ionic magnetic fluids

The properties of lyotropic ferronematic liquid crystals based on new Ni, Cu and Zn ionic magnetic fluids are discussed. The efficiency of these new ferrofluids in the lyotropic nematic liquid crystal doping is verified and compared with the conventional surfacted ferro fluid lyotropic doping. It was observed that the structural characteristics of the lyotropics and ferro fluids determine the good formation of the ferronematics

X-DLVO interactions between Nanocolloidal Magnetic Particles : the quantitative interpretation of the pH-dependent phase diagram of EDL-MF

The phase behavior of acidic samples of EDL-MF based on cobalt ferrite nanoparticles with controlled mean sizes was investigated at constant temperature and in absence of magnetic field. By monitoring the anoparticle charge by pH adjustments, we constructed an experimental pH-dependent phase diagram for all samples that revealed sol, gel thixotropic or coagulated phases in different pH regions. Then, by using an extended DLVO potential we analyzed quantitatively the observed phase diagram in function of pH and nanoparticle mean size

Surface charge density determination in water based magnetic colloids : a comparative study

This work focuses on the systematic investigation of the two well-established methods of structural surface charge density determination on magnetic colloids, labeled as Single Potentiometric Method (SPM) and Potentiometric-Conductometric Method (PCM). To compare some important features of the methods we determined the structural surface charge density of magnetic colloids samples based on CoFe2O4@ɣ-Fe2O3 core-shell nanoparticles with three different mean sizes using both strategies. Concerning quickness, easiness and cost, the PCM has proved to be more advantageous than the SPM. Regarding the effectiveness, both methods were consistent in determining the saturation value of the structural charge, but the SPM was more accurate to describe the pH-dependence of the concentration of the charged surface sites. Considering the chemical safety, the methods are equivalent. Finally, both the SPM and PCM are reproducible and can be effectively applied to determine the saturation value of the surface charge density on magnetic colloids

Static magneto optical birefringence of New Electric Double Layered Magnetic Fluids

Magnetic birefringence measurements are performed under a static eld on Electric Double Layered Magnetic Fluids based on copper and zinc ferrite nanostructures. The optical birefringence is related to a single-particle e ect and well described by a Langevin model which includes a lognormal distribution of particles. By the eld-induced birefringence level, these new magnetic fluids are comparable to usual ones, a result which could o er a new way for biological applications

Désordre de spins, anisotropie magnétique et magnéto-optique de nanoparticules de ferrites

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceBrazilFRB

Etude des propriétés structurelles locales de liquides magnétiques (de la nanoparticule à la solution)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Etude des propriétés structurelles locales de liquides magnétiques (de la nanoparticule à la solution)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Electric Double Layered Magnetic Fluids (EDL-MF) based on spinel ferrite nanostructures [(M1-x+2Fex+3)]A [(Fe2-x+3 Mx+2)]BO4-2

This paper presents a review of Electric Double Layered Magnetic Fluids (EDL-MF) based on spinel ferrite type [(M1-x+2Fex+3)]A [(Fe2-x+3 Mx+2)]BO4-2, with M(II) = Mn, Co, Ni, Cu and Zn. The chemical synthesis of the nanoparticles using hydrothermal techniques and their complete peptization in an aqueous medium results in a ultra stable magnetic colloid, EDL-MF. The characterization of the particles was performed using X-ray diffraction and electronic microscopy techniques. The resulted sols were investigated by magnetic, magneto-optical measurements and magnetic resonance techniques

Colloidal stability and concentration effects on nanoparticle heat delivery for magnetic fluid hyperthermia

The heat produced by magnetic nanoparticles, when they are submitted to a time-varying magnetic field, has been used in many auspicious biotechnological applications. In the search for better performance in terms of the specific power absorption (SPA) index, researchers have studied the influence of the chemical composition, size and dispersion, shape, and exchange stiffness in morphochemical structures. Monodisperse assemblies of magnetic nanoparticles have been produced using elaborate synthetic procedures, where the product is generally dispersed in organic solvents. However, the colloidal stability of these rough dispersions has not received much attention in these studies, hampering experimental determination of the SPA. To investigate the influence of colloidal stability on the heating response of ferrofluids, we produced bimagnetic core@shell NPs chemically composed of a ZnMn mixed ferrite core covered by a maghemite shell. Aqueous ferrofluids were prepared with these samples using the electric double layer (EDL) as a strategy to maintain colloidal stability. By starting from a proper sample, ultrastable concentrated ferrofluids were achieved by both tuning the ion/counterion ratio and controlling the water content. As the colloidal stability mainly depends on the ion configuration on the surface of the magnetic nanoparticles, different levels of nanoparticle clustering are achieved by changing the ionic force and pH of the medium. Thus, the samples were submitted to two procedures of EDL destabilization, which involved dilution with an alkaline solution and a neutral pH viscous medium. The SPA results of all prepared ferrofluid samples show a reduction of up to half the efficiency of the standard sample when the ferrofluids are in a neutral pH or concentrated regime. Such results are explained in terms of magnetic dipolar interactions. Our results point to the importance of ferrofluid colloidal stability in a more reliable experimental determination of the NP heat generation performance.Authors gratefully acknowledge the financial support of the Brazilian agencies CAPES, CNPq (grants 465259/2014-6, 202340/2015-5, 400849/2016-0, 305796/2016-0, and 422740/2018-7), INCT-FCx (grant 2014/50983-3), and FAP-DF (grants 0193.001569/2017, 0193.001376/2016, and 0193.000.919/2016).Peer reviewe