Ansis Mezulis

Soret coefficient of nanoparticles in ferrofluids in the presence of a magnetic field

Experiments on a nonstationary separation of nanometer-sized Mn0.5Zn0.5Fe2O particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for a one-dimensional mixed (thermal and concentration) convection in the column, the Soret coefficient of lyophilized nanoparticles from the separation curves are calculated. It is shown that in a zero magnetic field particles are transferring toward decreasing temperatures. The thermal diffusion ratio αT reaches a value αT≈+20. A significant influence of a uniform magnetic field B on particle separation is observed. If B is oriented along the temperature gradient ∇T, a strong decrease in thermal diffusion coefficient takes place whereas the transversal field B⊥∇T causes an intensification of particle thermophoretic transfer. Both effects qualitatively well agree with theoretical predictions based on a hydrodynamic theory of particle thermomagnetophoretic motion.

Thermal diffusion of magnetic nanoparticles in ferrocolloids: Experiments on particle separation in vertical columns

Abstract Experiments on nonstationary separation of nanometer-sized Fe 3 O 4 particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for an one-dimensional mixed (thermal and concentration) convection in the column, the Soret coefficient of magnetic nanoparticles are calculated. It is shown that particles are transferred in the direction of decreasing temperature. The thermal diffusion ratio α T for magnetite particles suspended in tetradecane reaches the value α T ≈ − 20. Neithera dependence of α T on temperature nor any changes in particle-size distribution curves during the separation are observed.

On the microconvective instability in optically induced gratings

In the present work, attention is paid to some significant effects (phenomena) in forced Rayleigh scattering (FRS) experiments with an applied magnetic field, ∇T∥H, which have not been analyzed before. In the work we deal with an idea that the experimentally observed effects are caused by microconvection [M. Igonin, Magnetohydrodynamics 37, 3 (2001); A. Cebers and M. Igonin, Magnetohydrodynamics 38, 265 (2002)]. The dimensionless numbers Cm and Rm, which are responsible for the onset of microconvection, are calculated from experiments as well as from the linear stability analysis in a Hele-Shaw approximation [M. Igonin, Magnetohydrodynamics 37, 3 (2001)]. The problem of the definition of the true values of diffusion and Soret coefficients from experiments and their field dependence, which are not affected by the assumed microconvection, is solved by original data processing. Visual observation of the FRS experiment provides additional information, applicable for a further analysis.

Magnetic Soret effect in a hydrocarbon based colloid containing surfacted Mn–Zn ferrite particles

Abstract The Soret effect has been investigated in a hydrocarbon based magnetic fluid containing surfacted Mn 0.5 Zn 0.5 Fe 2 O 4 nanoparticles with a magnetic volume concentration of 2.3%. The magnetic fluid fills up a vertical diffusion column which consists of a flat vertical channel between two walls and two reservoirs at the ends of the channel. One wall of the channel is being heated while the another one is cooled, maintaining a temperature gradient over the channels width that leads to separation of particles due to the Soret effect as well as the convective flow in the channel. The combination of the two mentioned effects brings up a measurable change of the concentration of magnetic particles in both reservoirs. The results have been obtained for uniform magnetic fields, aligned parallelly and normally to the temperature gradient respectively, by measuring the concentration of magnetic particles in the reservoirs. Obtained results are in good qualitative agreement with thermodiffusion column theory, published earlier (E. Blums, J. Magn. Magn. Mater. 149 (1995) 111).

Thermodiffusion motion of electrically charged nanoparticles

The present work deals with experimental studies to examine the theoretical model of thermodiffusion of electrically charged nanoparticles. Three different ionic magnetic colloid samples have been synthesized and profoundly analyzed. The theoretical model is a classical one, based on the calculation of the temperature and the electric potential distribution around nanoparticles. The discrepancy between experimental data and theory turns out not to exceed 20%. We focus on applying different approximations between calculated electrical double layer in the theoretical model and experimental determination of the surface charge density of colloidal particles. We assume this is the main reason for obtained discrepancy.

The Presence of Microconvective Instability in Optically Induced Gratings

Abstract In the present work, attention is paid to some significant effects (phenomena) in forced Rayleigh scattering (FRS) experiments with an applied magnetic field, ∇ T ∥ H, which have not been analyzed before. The work deals with the idea that the experimentally observed effects are caused by microconvection. The dimensionless numbers Cm and Rm, which are responsible for the onset of microconvection, are calculated from experiments as well as from the linear stability analysis in a Hele-Shaw approximation. The problem of definition of the true values of diffusion and Soret coefficients from experiments and their field dependence, which are not affected by the assumed microconvection, is solved by original data processing.