Effect of drop-like aggregates on the viscous stress in magnetic suspensions

We present results of theoretical and experimental study of effect of dense drop-like aggregates on the magnetoviscous effects in suspensions of non-Brownian magnetizable particles. Unlike the previous works on this subject, we do not restrict ourselves by the limiting case of highly elongated drops. This allows us to reproduce the experimental rheological curve in wide region of the shear rate of the suspension flow.This work has been supported by the Russian Fund of Fundamental Investigations, Grants 12-01-00132, 13-02-91052, 13-01-96047 and 14-08-00283; by the Act 211 Government of the Russian Federation No. 02.A03.21.0006; by the Junta de Andalucía (Spain), Project P09-FQM-4787; and by the University of Granada (Acción Integrada con Russia; Plan Propio 2011); and CNRS PICS No. 6102 is also acknowledged

Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields

When a micron-sized magnetizable particle is introduced into a suspension of nanosized magnetic particles, the nanoparticles accumulate around the microparticle and form thick anisotropic clouds extended in the direction of the applied magnetic field. This phenomenon promotes colloidal stabilization of bimodal magnetic suspensions and allows efficient magnetic separation of nanoparticles used in bioanalysis and water purification. In the present work, size and shape of nanoparticle clouds under the simultaneous action of an external uniform magnetic field and the flow have been studied in details. In experiments, dilute suspension of iron oxide nanoclusters (of a mean diameter of 60 nm) was pushed through a thin slit channel with the nickel microspheres (of a mean diameter of 50$\mu$m) attached to the channel wall. The behavior of nanocluster clouds was observed in the steady state using an optical microscope. In the presence of strong enough flow, the size of the clouds monotonically decreases with increasing flow speed in both longitudinal and transverse magnetic fields. This is qualitatively explained by enhancement of hydrodynamic forces washing the nanoclusters away from the clouds. In the longitudinal field, the flow induces asymmetry of the front and the back clouds. To explain the flow and the field effects on the clouds, we have developed a simple model based on the balance of the stresses and particle fluxes on the cloud surface. This model, applied to the case of the magnetic field parallel to the flow, captures reasonably well the flow effect on the size and shape of the cloud and reveals that the only dimensionless parameter governing the cloud size is the ratio of hydrodynamic-to-magnetic forces - the Mason number. At strong magnetic interactions considered in the present work (dipolar coupling parameter $\alpha \geq 2$), the Brownian motion seems not to affect the cloud behavior

On the theory of magnetoviscous effect in magnetorheological suspensions

Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The following article appeared in Zubarev, A.; et al. On the theory of magnetoviscous effect in magnetorheological suspensions. Journal of Rheology, 58: 1673 (2014) and may be found at http://dx.doi.org/10.1122/1.4889902A theoretical model of magnetoviscous effect in a suspension of nonBrownian linearly magnetizable particles is suggested. A simple shear flow in the presence of an external magnetic field aligned with the velocity gradient is considered. Under the action of the applied field, the particles are supposed to form dense highly elongated droplike aggregates. Two different scenarios of the aggregates’ destruction under shearing forces are considered, namely, a “bulk” destruction of aggregates into pieces and an “erosive” destruction connected to the rupture of individual particles from the aggregate surface. Both models are based on a balance of forces acting either on the whole aggregate or on individual particles. The two approaches lead to qualitatively different Mason number (Ma) behaviors of the magnetic suspensions: The suspension viscosity scales as either Ma^-2/3 for the bulk destruction of aggregates or Ma^-4/5 for the erosive destruction. In any case, we do not recover Bingham behavior (Ma^-1) often predicted by chain models of the magneto- or electrorheology. Our theoretical results are discussed in view of comparison with existing theories and experimental results in the wide range of Mason numbers.This work has been done under support of Russian Fund of Fundamental Investigations, Grant Nos. 12-01-00132, 13-02-91052, 13-01-96047, and 14-08-00283; by the Act 211 Government of the Russian Federation No. 02.A03.21.0006. The University of Granada (Acción Integrada con Rusia; Plan Propio 2011), as well as project CNRS PICS No. 6102 are also acknowledged for their financial support

Magnetorheological effect in the magnetic field oriented along the vorticity

Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The following article appeared in Kuzhir, P.; et al. Magnetorheological effect in the magnetic field oriented along the vorticity. Journal of Rheology, 58: 1829 (2014) and may be found at http://dx.doi.org/10.1122/1.4893586.In this work, we have studied the magnetorheological (MR) fluid rheology in the magnetic field parallel to the fluid vorticity. Experimentally, the MR fluid flow was realized in the Couette coaxial cylinder geometry with the magnetic field parallel to the symmetry axis. The rheological measurements were compared to those obtained in the cone-plate geometry with the magnetic field perpendicular to the lower rheometer plate. Experiments revealed a quasi-Bingham behavior in both geometries with the stress level being just a few dozens of percent smaller in the Couette cylindrical geometry at the same internal magnetic field. The unexpectedly high MR response in the magnetic field parallel to the fluid vorticity is explained by stochastic fluctuations of positions and orientations of the particle aggregates. These fluctuations are induced by magnetic interactions between them. Once misaligned from the vorticity direction, the aggregates generate a high stress independent of the shear rate, and thus assimilated to the suspension apparent (dynamic) yieldstress. Quantitatively, the fluctuations of the aggregate orientation are modeled as a rotary diffusion process with a diffusion constant proportional to the mean square interaction torque. The model gives a satisfactory agreement with the experimental field dependency of the apparent yield stress and confirms the nearly quadratic concentration dependency rY / U2:2, revealed in experiments. The practical interest of this study lies in the development of MR smart devices with the magnetic field nonperpendicular to the channel walls.This work has been supported by Projects P09-FQM-4787 (Junta de Andalucıa, Spain), “Factories of the Future” (Grant No. 260073, DynExpert FP7) and PICS 161801 project: “Magnetic nanocomposites for mechanical and biological applications” with Ural Federal University, Russia. In addition, L.R.-A. acknowledges financial support by Secretarıa de Estado de Educacion, Formacion Profesional y Universidades (MECD, Spain) through its FPU and Estancias Breves programs

Rheology of magnetic alginate hydrogels

Según Sherpa/Romeo el periodo de embargo es de 12 mesesMagnetic hydrogels are becoming increasingly in demand for technical and biomedical applications, especially for tissue engineering purposes. Among them, alginate-based magnetic hydrogels emerge as one of the preferred formulations, due to the abundance, low cost, and biocompatibility of alginate polymers. However, their relatively slow gelation kinetics provokes strong particle settling, resulting in nonhomogeneous magnetic hydrogels. Here, we study magnetic hydrogels prepared by a novel two-step protocol that allows obtaining macroscopically homogeneous systems, consisting of magnetic microparticles embedded within the alginate network. We describe a comprehensive characterization (morphology, microstructure, and mechanical properties under shear stresses) of the resulting magnetic hydrogels. We pay special attention to the effects of particle volume fraction (up to 0.33) and strength of the magnetic field on the viscoelastic properties of the magnetic hydrogels. Our results indicate that magnetic hydrogels are strongly strengthened against shear stresses as magnetic particle concentration and applied field intensity increase. Finally, we report an adaptation of the two-step protocol for the injection of the magnetic hydrogels that might be adequate for implementation in vivo. Interestingly, injected magnetic hydrogels present similar morphology and mechanical properties to noninjected hydrogels. To conclude, we report magnetic alginate hydrogels with adequate homogeneity and injectability character. These characteristics, together with the broad range of their mechanical properties, make them perfect candidates for cutting-edge technology.FIS2013-41821-R (Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica, MINECO, Spain, cofunded by ERDF, European Union) and FIS2017-85954-R (Ministerio de Economía, Industria y competitividad, MINECO, and Agencia Estatal de Investigación, AEI, Spain, cofunded by Fondo Europeo de Desarrollo Regional, FEDER, European Union). Ministry of Education and Science of the Russian Federation, projects 02.A03.21.0006, 3.1438.2017/4.6, and 3.5214.2017/6.7, as well as to the Russian Fund of Basic Researches, project 18-08-00178. French government, piloted by the National Research Agency (ANR) in the framework of the project Future Investments UCA JEDI, Ref. No. ANR-15-IDEX-01 (RheoGels).

Two-stage kinetics of field-induced aggregation of medium-sized magnetic nanoparticles

The present paper is focused on the theoretical and experimental study of the kinetics of field-induced aggregation of magnetic nanoparticles of a size range of 20-100 nm. Our results demonstrate that (a) in polydisperse suspensions, the largest particles could play a role of the centers of nucleation for smaller particles during the earliest heterogeneous nucleation stage; (b) an intermediate stage of the aggregate growth (due to diffusion and migration of individual nanoparticles towards the aggregates) is weakly influenced by the magnetic field strength, at least at high supersaturation; (c) the stage of direct coalescence of drop-like aggregates (occurring under magnetic attraction between them) plays a dominant role at the intermediate and late stages of the phase separation, with the time scale decreasing as a square of the aggregate magnetization

Protein identification using a nanoUHPLC-AP-MALDI MS/MS workflow with CID of multiply charged proteolytic peptides

Liquid AP-MALDI can produce predominantly multiply charged ESI-like ions and stable durable analyte ion yields with samples allowing good shot-to-shot reproducibility and exhibiting self-healing properties during laser irradiation. In this study, LC-MALDI MS/MS workflows that utilize multiply charged ions are reported for the first time and compared with standard LC-ESI MS/MS for bottom-up proteomic analysis. The proposed method is compatible with trifluoroacetic acid as an LC ion pairing reagent and allows multiple MS/MS acquisitions of the LC-separated samples without substantial sample consumption. In addition, the method facilitates the storage of fully spotted MALDI target plates for months without significant sample degradation

Investigation and optimization of parameters affecting the multiply charged ion yield in AP-MALDI MS

Liquid matrix-assisted laser desorption/ionization (MALDI) allows the generation of predominantly multiply charged ions in atmospheric pressure (AP) MALDI ion sources for mass spectrometry (MS) analysis. The charge state distribution of the generated ions and the efficiency of the ion source in generating such ions crucially depend on the desolvation regime of the MALDI plume after desorption in the AP-tovacuum inlet. Both high temperature and a flow regime with increased residence time of the desorbed plume in the desolvation region promote the generation of multiply charged ions. Without such measures the application of an electric ion extraction field significantly increases the ion signal intensity of singly charged species while the detection of multiply charged species is less dependent on the extraction field. In general, optimization of high temperature application facilitates the predominant formation and detection of multiply charged compared to singly charged ion species. In this study an experimental setup and optimization strategy is described for liquid AP-MALDI MS which improves the ionization effi- ciency of selected ion species up to 14 times. In combination with ion mobility separation, the method allows the detection of multiply charged peptide and protein ions for analyte solution concentrations as low as 2 fmol/lL (0.5 lL, i.e. 1 fmol, deposited on the target) with very low sample consumption in the low nL-range

Dyson-Schwinger Equations: Density, Temperature and Continuum Strong QCD

Continuum strong QCD is the application of models and continuum quantum field theory to the study of phenomena in hadronic physics, which includes; e.g., the spectrum of QCD bound states and their interactions; and the transition to, and properties of, a quark gluon plasma. We provide a contemporary perspective, couched primarily in terms of the Dyson-Schwinger equations but also making comparisons with other approaches and models. Our discourse provides a practitioners' guide to features of the Dyson-Schwinger equations [such as confinement and dynamical chiral symmetry breaking] and canvasses phenomenological applications to light meson and baryon properties in cold, sparse QCD. These provide the foundation for an extension to hot, dense QCD, which is probed via the introduction of the intensive thermodynamic variables: chemical potential and temperature. We describe order parameters whose evolution signals deconfinement and chiral symmetry restoration, and chronicle their use in demarcating the quark gluon plasma phase boundary and characterising the plasma's properties. Hadron traits change in an equilibrated plasma. We exemplify this and discuss putative signals of the effects. Finally, since plasma formation is not an equilibrium process, we discuss recent developments in kinetic theory and its application to describing the evolution from a relativistic heavy ion collision to an equilibrated quark gluon plasma.Comment: 103 Pages, LaTeX, epsfig. To appear in Progress in Particle and Nuclear Physics, Vol. 4