Papers by Keyword: Ferrofluids

Abstract: Candidiasis is an infection caused by the fungus C. albicans. Ferrofluid Zn_0.2Fe_2.8O₄/Ag is the best candidate to overcome the problem of infection caused by this fungus. In addition to the safe ingredients used, its ability to create ROS and maintain stability has the potential to be an excellent antifungal agent. The purpose of this study was to create a new ferrofluid with double surfactants for the antifungal C. albicans. Zn_0.2Fe_2.8O₄/Ag ferrofluids were synthesized using a bottom-up method, starting from the synthesis of Zn_0.2Fe_2.8O₄ nanoparticles, Zn_0.2Fe_2.8O₄/Ag nanocomposites, to the synthesis of Zn_0.2Fe_2.8O₄/Ag ferrofluids. Zn_0.2Fe_2.8O₄/Ag powder was characterized using XRD and SEM to determine the particle structure and morphology. Meanwhile, Zn_0.2Fe_2.8O₄/Ag ferrofluids were characterized using FTIR and antifungal activity tests to determine the functional group and zone of inhibition against the growth of the fungus C. albicans. The results of the characterization analysis showed that Zn_0.2Fe_2.8O₄/Ag nanoparticles had good crystallinity, with a crystallite size of Zn_0.2Fe_2.8O₄/Ag of 11.32 nm and an Ag crystallite size of 7.00 nm. SEM characterization showed that Zn_0.2Fe_2.8O₄/Ag nanoparticles had agglomeration with the average particle size distribution of 443 nm. The functional groups detected by FTIR confirmed the success of the ferrofluid synthesis Zn_0.2Fe_2.8O₄/Ag where spinel functional groups, olefin groups, and functional groups S=O were formed. The results of the antifungal activity test showed that Zn_0.2Fe_2.8O₄/Ag ferrofluids were relatively active as an antifungal agent, with a diameter of the C. albicans growth inhibition zone of 9.63 mm.

Abstract: The recent development of the using the magnetic nanoparticles for hyperthermia treatments emphasizes the needed of smart materials to become a safety for heat therapy. Self-regulate magnetic nanoparticles of MnZnFe₂O₄ may be proper for thermal treatments. Structure and magnetic properties of the synthesis Mn_1-xZn_x Fe₂O₄ with x=0- 0.5 by step 0.1were studied. Superparamagnetic nanoparticles of MnZnFe₂O₄ were prepared by co-precipitation method, followed that heat treatment in the autoclave reactor. XRD results showed that is difficult to prepare MnZnFe₂O₄ directly using the co-precipitation method. Preparation method yield nanoparticles with spherical shape and there is a slight change in the particle size distribution, also observed shrinkage occurs in the particle size after heat treatments, the average particle size was estimated about 20nm as confirmed by FESEM images. FTIR spectra of samples showed two distinct absorption peaks in the range ~ 617 – 426 (cm^-1) related to stretching vibrations of the (Fe-O) in the tetrahedral and octahedral side respectively. Magnetic measurements were carried out using (VSM), M-H curves indicate typical soft magnetic materials and particles so small to be identical superparamagnetic nanoparticles. Heating ability of water based colloidal dispersions of samples were studied under magnetic field strength 6.5kA/m and the frequency 190 kHz, and the results showed when increasing Zn²⁺ to x=0.3 or more the samples not heated up. Depending on the heating curve susceptibility, effective relaxation time 𝜏 and Néel relaxation time , were determined.

Abstract: Magnetic magnetite, Fe₃O₄ nanoparticles produced by Massart’s procedure were used to prepare water based magnetite, Fe₃O₄ ferrofluids without addition of any stabilizing agent or surfactant. The thermal properties and suspension stabilization of the ferrofluids were investigated by varying the magnetite, Fe₃O₄ nanoparticles concentration in the ferrofluids prepared. The thermal conductivity of water based ferrofluids prepared using five different volume fraction of magnetite, Fe₃O₄ suspension (0.1, 0.05, 0.02, 0.01 and 0.005) were measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C in order to evaluate its potential application as heat transfer fluid. The results shows that the thermal conductivity of the ferrofluids are higher than the base fluid, and the thermal conductivity of the ferrofluids increased as the magnetite concentration in the ferrofluids decreased however reached its optimum for ferrofluids prepared using 0.01 volume fraction of magnetite suspension over 0.99 volume fraction of water. Accordingly, the thermal conductivity of the ferrofluids significantly increased as the temperature increased where 49.4% enhancement with respect to water were observed at temperature 60°C.

Abstract: This Composite Fe-C anode sputtering in a low-pressure arc discharge has been used to produce Fe-containing nanoparticles on a carbon matrix. Magnetic susceptibility as a function of background pressure has been measured. The data obtained showed the complex, no-monotonous dependency. The material synthesized at optimal pressure (maximal value of magnetic susceptibility) was investigated by means of transmission electron microscopy, X-ray diffraction and magnetometry. Size distribution function of iron containing nanoparticles has been measured. Chemical composition includes iron, iron carbide and carbon soot. Saturation magnetization have been measured and it was shown that the synthesized material is superparamagnetic. The physical processes resulting in the complex behavior of magnetic susceptibility are discussed.

Abstract: Two different bidisperse approximations of one gamma-distribution were examined in the present manuscript. The bidisperse system was chosen as the first step to allow for polydispersity when studying thermodynamics and microstructure of magnetic fluids. The author used the first-order modified mean-field model for investigating magnetization curves for these approximations and showed that curves are almost identical. Also analyzed was the influence of choosing variant of constructed bidisperse model on the structure factors, which were constructed using the mathematical model, developed in the paper by Novak et al. [J.Chem.Phys. 139 (2013) 224905].

Abstract: This paper investigates the dynamic characteristics of parabolic film slider bearing operating with ferrofluids. Comparing with the slider bearing of an inclined plane film, the parabolic film slider bearing operating with ferrofluids in the presence of external magnetic fields provide higher better dynamic stiffness and damping performances.

Abstract: We discuss materials which owe their stability to external elds. These include: 1)external electric or magnetic elds, and 2) quantum vacuum uctuations in these elds inducedby suitable boundary conditions (the Casimir e ect). Instances of the rst case include theoating water bridge and ferrouids in magnetic elds. An example of the second case is takenfrom biology where the Casimir e ect provides an explanation of the formation of stackedaggregations or \rouleaux" by negatively charged red blood cells. We show how the interplaybetween electrical and Casimir forces can be used to drive self-assembly of nano-structuredmaterials, and could be generalized both as a probe of Casimir forces and as a means ofmanufacturing nanoscale structures. Interestingly, all the cases discussed involve the generationof the somewhat exotic negative pressures. We note that very little is known about the phasediagrams of most materials in the presence of external elds other than those represented bythe macroscopic scalar quantities of pressure and temperature. Many new and unusual statesof matter may yet be undiscovered.

Abstract: Magnetorheological (MR), Electrorheological (ER), and Ferrofluids are considered as a class of smart materials due to their novel behavior under an external stimulus such as a magnetic and electrical field. The behavior of these synthetic fluids offer techniques for achieving efficient heat and mass transfer, damping, drag reduction, wetting, fluidization, sealing, and more. Magnetorheological fluids are suspensions of non-colloidal, multi-domain and magnetically soft particles organic and aqueous liquids. Electrorheological fluids are suspensions of electrically polarizable particles dispersed in electrically insulating oil. Ferrofluids are known as magnetic liquids that are colloidal suspensions of ultrafine, single domain magnetic particles in either aqueous or non-aqueous liquids. In this review article a history of these fluids is given, together with a description of their synthesis in terms of stability and redisperibility and how it is understood in various parts of the science and technology. Then the structural changes and rheological properties of these smart fluids under an external stimulus together with a series of applications are presented.

Abstract: Fe3O4 ferrofluids with uniform magnetic particles were prepared via improved chemical coprecipation technique. A narrow distribution of 8.6-10.8 nm particle sizes was obtained from the magnetization curve using the free-form-model based on Bayesian inference theory. The mean particle diameter about 9.8 nm is consistent with the XRD and SEM results. The hydrodynamic properties of ferrofluids were investigated with different applied magnetic field and shear rate. The experimental results show that diluted ferrofluid and concentrated ferrofluid are Newtonian-fluid and Bingham-plastic fluid, respectively.

Abstract: Magnetic nano- and microparticles have already found many important applications in various areas of biosciences, medicine, biotechnology, environmental technology etc. These smart materials exhibit different types of response to external magnetic field. In most cases they can be described as composite materials, where the magnetic properties are caused by the presence of iron oxides nano- or microparticles. Such materials can be efficiently separated from difficult-to-handle samples and targeted to the desired place, applied as contrast agents for magnetic resonance imaging, used to generate heat during exposure to alternating magnetic field or to modify biomolecules and biological structures.