Magnetorheological behavior of magnetite covered clay particles in aqueous suspensions

Montmorillonite clay particles coated with magnetite nanoparticles suspended in aqueous media behave as magnetorheological fluids with enhanced stability as compared to conventional ones. In this work, the study of the magnetorheological behavior of these suspensions of magnetite-clay composite particles has been carried out. For this purpose, both steady and dynamic rheological measurements were carried out in the absence and in the presence of external magnetic fields. In the first kind of experiments, the rheograms of the suspensions (shear stress versus shear rate plot) are analyzed as a function of the strength of the magnetic field applied. In the second one, oscillatory stresses are applied to the system, and the storage modulus is studied as a function of the external magnetic field. In the absence of magnetic field, the suspensions develop a weak yield stress due to the aggregation of the magnetite covered clay particles. In the presence of magnetic field, the yield stress is strongly dependent on the magnetic field strength inside the samples, demonstrating that the suspensions experience a magnetorheological effect, moderate when the magnetic field strength is weak and stronger for values of magnetic field higher than 150–200 kA/m. Actually, the most intriguing result is the change of the trend in the dependence of the yield stress with the field. This dependence is approximately linear with the field for strength values smaller than 150–200 kA/m. On the other hand, for higher values, the yield stress increases with magnetic field following a power law with exponent 4.5.The results are interpreted by means of a model that relates the structure of the particles in the suspensions to the magnetic field applied and using the interaction energy between particles calculated by the extended DLVO theory to include magnetic interaction.Financial support by Ministerio de Ciencia e Innovación (Spain) under project No FIS2009-07321, and Junta de Andalucía (Spain) under Project Nos. P08-FQM-3993 and P09-FQM-4787 is gratefully acknowledge

Inverse magnetorheological fluids

We report a new kind of field-responsive fluids consisting of suspensions of diamagnetic (DM) and ferromagnetic (FM) microparticles in ferrofluids. We designate them as inverse magnetorheological (IMR) fluids for analogy with inverse ferrofluids (IFFs). Observations on the particle self-assembly in IMR fluids upon magnetic field application showed that DM and FM microparticles were assembled into alternating chains oriented along the field direction. We explain such assembly on the basis of the dipolar interaction energy between particles. We also present results on the rheological properties of IMR fluids and, for comparison, of IFFs and bidispersed magnetorheological (MR) fluids. Interestingly, we found that upon magnetic field, the rheological properties of IMR fluids were enhanced with respect to bidispersed MR fluids with the same FM particle concentration, by an amount greater than the sum of the isolated contribution of DM particles. Furthermore, the field-induced yield stress was moderately increased when up to 30 % of the total FM particle content was replaced with DM particles. Beyond this point, the dependence of the yield stress on the DM content was non-monotonic, as expected for FM concentrations decreasing to zero. We explain these synergistic results by two separate phenomena: the formation of exclusion areas for FM particles due to the perturbation of the magnetic field by DM particles, and the dipole-dipole interaction between DM and FM particles, which enhances the field-induced structures. Based on this second phenomenon, we present a theoretical model for the yield stress that semi-quantitatively predicts the experimental results.Projects 12-01-00132, 13-02-91052, 13-01-96047, 14-08-00283 (Russian Fund of Fundamental Investigations), 2.1267.2011 (Ministry of Education of Russian Federation), the Act 211 (Government of the Russian Federation № 02.A03.21.0006). The University of Granada (Acción Integrada con Rusia; Plan Propio 2011). L. Rodríguez-Arco acknowledges financial support by Secretaría de Estado de Educación, Formación Profesional y Universidades (MECD, Spain) through its FPU program

Scaling between viscosity and hydrodynamic/magnetic forces in magnetic fluids

The aim of this work is the investigation of the magnetorheological behavior, under both simple steady- and oscillatory-shear flow regimes, of fluids composed by micron-sized iron particles (average diameter 930 ± 330 nm) dispersed in silicone oil. Magnetic fields ranging from 279 A/m (0.35 mT) to 1727 A/m (2.17 mT) were applied to the suspensions. The effect of silica nanoparticles as stabilizer of the suspensions has also been considered. The study has been made by the scaling between the viscosity of the suspension and the ratio of hydrodynamic to magnetic forces acting on the dispersed particles, given by the dimensionless Mason number (Mn), and interpreted in terms of the chainlike model taken from the theory of Martin and Anderson (J. Chem. Phys. 104 (1996) 4814-4827). The model is quite well accomplished for iron suspensions of different (20 % and 30 %) volume fraction without any stabilizing agent. The presence of added silica nanoparticles in the suspension hinders the formation of regular iron structures induced by the magnetic field, especially at the lowest applied magnetic fields. Thus the model becomes not applicable to these cases. Viscometry has been shown to be more adequate than oscillometry for scaling the viscous properties of magnetorheological suspensions with microscopic interparticle forces in terms of Mn number.Financial support from MEC (Spain) and FEDER funds (EU) (Project MAT2005-07746-C02-01) and Junta de Andalucía, Spain (PE-FQM-410) are gratefully acknowledged

Role of particle clusters on the rheology of magneto-polymer fluids and gels

Even in absence of cross-linking, at large enough concentration, long polymer strands have a strong influence on the rheology of aqueous systems. In this work, we show that solutions of medium molecular weight (120,000 – 190,000 g/mol) alginate polymer retained a liquid-like behaviour even for concentrations as large as 20 % w/v. On the contrary, solutions of alginate polymer of larger (and also polydisperse) molecular weight (up to 600,000 g/mol) presented a gel-like behaviour already at concentrations of 7 % w/v. We dispersed micron-sized iron particles at a concentration of 5 % v/v in these solutions, which resulted either in stable magnetic fluids or gels, depending on the type of alginate polymer employed (medium or large molecular weight, respectively). These magneto-polymer composites presented a shear-thinning behaviour that allowed injection through a syringe and recovery of the original properties afterwards. More interestingly, application of a magnetic field resulted in the formation of particle clusters elongated along the field direction. The presence of these clusters intensely affected the rheology of the systems, allowing a reversible control of their stiffness. We finally developed theoretical modelling for the prediction of the magnetic-sensitive rheological properties of these magneto-polymer colloids.Ministerio de Economía, Industria y Competitividad, MINECO, and Agencia Estatal de Investigación, AEI, Spain, cofounded by Fondo Europeo de Desarrollo Regional, FEDER, European Union, project FIS2017-85954-R. Ministry of Education and Science of the Russian Federation, projects 02.A03.21.0006; 3.1438.2017/4.6; 3.5214.2017/6.7 as well as to the Russian Fund of Basic Researches, project 19-52-1202

On the effect of wall slip on the determination of the yield stress of magnetorheological fluids

We studythe effect ofwall slip on themeasuredvalues ofthe yield stress of magnetorheological (MR) fluids. For this aim we used a rheometer provided with parallel-plate geometries of two types, distinguished by having smooth or rough surfaces. We found that wall slip led to the underestimation of the yield stress when measuring geometries with smooth surfaces were used,and that this underestimation was more pronounced for the static than for the dynamic yield stress. Furthermore, we analysed the effect that both irreversible particle aggregation due to colloidal interactions and reversible magnetic field-induced particle aggregation had on the underestimation provoked by wall slip. We found that the higher the degree of aggregation the stronger the underestimation of the yield stress. At low intensity of the applied magnetic field irreversible particle aggregation was dominant and, thus, the underestimation of the yield stress was almost negligible for well-dispersed MR fluids, whereas it was rather pronounced for MR fluids suffering from irreversible aggregation. As the magnetic field was increased the underestimation of the yield stress became significant even for the best dispersedMR fluid.This study was supported by project FIS2013-41821-R (Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica, Ministerio de Economía y Competitividad, Spain, co-funded by ERDF, European Union), by the Russian Science Foundation, project 14-19-00989 and by Program of Ministry of Science and Education of the Russian Federation, project 3.12.2014/

Stability behaviour of composite magnetorheological fluids by an induction method

Este artículo puede consultarse en la siguiente dirección de la editorial: http://jim.sagepub.com/content/early/2015/03/26/1045389X15577656.full.pdf+htmlIn this work we study the stability behaviour of composite magnetorheological (MR) fluids consisting of magnetic (iron) and non-magnetic (poly (methylmethacrylate), PMMA) particles dispersed in mineral oil. Because of the opacity of the suspensions, optical methods traditionally employed for evaluation of the gravitational settling in colloidal suspensions are not suitable for sedimentation follow-up in this case. For this reason, we use an alternative method based on the evaluation of the resonant frequency of the inductance of a thin coil surrounding the sample The movement of the coil along the height of the container at specified steps and time intervals allows obtaining information about the local volume fraction of particles inside the tube. The obtained successive profiles for the multi-component suspensions show a decrease of the iron particle settling and of the initial rate of settling as the PMMA volume fraction is increased. Finally, the increase of the PMMA concentration gives rise to an improvement of the rheological properties upon magnetic field application for a given concentration of iron. Both a strongrheological response and a good colloidal stability are essential for practical applications.Proyectos PE2012-FQM694 (Junta de Andalucía, Spain)y FIS2013-47666-C3-1-R (Ministerio de Economía y Competitividad, Spain). L. R.-A. agrradece a la Universidad de Granada su contrato puente (Plan Propio de Investigación, UGR)

Biomedical applications of magnetic hydrogels

Hydrogels are used in biomedical applications thanks to their high-water content, porosity, and their ability to easily modify their properties (mechanical, chemical, microstructure, etc.). Hydrogels are the materials that most resemble the extracellular matrix of mammals. In recent years, magnetic hydrogels have become especially important. These are the result of combining magnetic nanoparticles with different hydrogel matrices. Among its properties, they have the ability to be remotely controlled modifying their physical properties, such as stability, stiffness and temperature (magnetic hyperthermia). Such unique characteristics make magnetic hydrogels very promising in biomedical applications such as, tissue engineering, drug delivery, biosensors, and cancer therapy. At this respect, this chapter focuses on the main biomedical applications of magnetic hydrogels and the most important discoveries on the subject.This study was supported by project 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). CGV acknowledges financial support by Ministerio de Ciencia, Innovación y Universidades and University of Granada, Spain, for her FPU17/00491 grant

In vitro characterization of a novel magnetic fibrin-agarose hydrogel for cartilage tissue engineering

The encapsulation of cells into biopolymer matrices enables the preparation of engineered substitute tissues. Here we report the generation of novel 3D magnetic biomaterials by encapsulation of magnetic nanoparticles and human hyaline chondrocytes within fibrin-agarose hydrogels, with potential use as articular hyaline cartilagelike tissues. By rheological measurements we observed that, (i) the incorporation of magnetic nanoparticles resulted in increased values of the storage and loss moduli for the different times of cell culture; and (ii) the incorporation of human hyaline chondrocytes into nonmagnetic and magnetic fibrin-agarose biomaterials produced a control of their swelling capacity in comparison with acellular nonmagnetic and magnetic fibrin-agarose biomaterials. Interestingly, the in vitro viability and proliferation results showed that the inclusion of magnetic nanoparticles did not affect the cytocompatibility of the biomaterials. What is more, immunohistochemistry showed that the inclusion of magnetic nanoparticles did not negatively affect the expression of type II collagen of the human hyaline chondrocytes. Summarizing, our results suggest that the generation of engineered hyaline cartilage-like tissues by using magnetic fibrin-agarose hydrogels is feasible. The resulting artificial tissues combine a stronger and stable mechanical response, with promising in vitro cytocompatibility. Further research would be required to elucidate if for longer culture times additional features typical of the extracellular matrix of cartilage could be expressed by human hyaline chondrocytes within magnetic fibrin-agarose hydrogels.This study was supported by projects FIS2013-41821-R (Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica, Ministerio de Economía, Industria y Competitividad, MINECO Spain, cofunded by Fondo Europeo de Desarrollo Regional, FEDER, European Union), 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), and by the Consejería de Salud y Familias, Junta de Andalucía, Spain, Grant SAS CS PI-0257-2017

Influence of the chirality of short peptide supramolecular hydrogels in protein crystallogenesis

For the first time the influence of the chirality of the gel fibers in protein crystallogenesis has been studied. Enantiomeric hydrogels 1 and 2 were tested with model proteins lysozyme and glucose isomerase and a formamidase from B. cereus. Crystallization behaviour and crystal quality of these proteins in both hydrogels are presented and compared.MICINN (Spain) projects BIO2010-16800 (JAG), CTQ-2011.22455 (LAC & JMC), CTQ2012-34778 (JJDM & ALG), “Factoría Española de Cristalización” Consolider-Ingenio 2010 (JAG & MCM) and EDRF Funds (JAG, LAC & JMC), P12-FQM-2721 (LAC) Junta de Andalucía.MINECO,Project No. FIS2013-41821-R

The role of thermal diffusion, particle clusters, hydrodynamic and magnetic forces on the flow behaviour of magneto-polymer composites

In this paper, we study the shear-induced flow of magneto-polymer composites, consisting of dispersions of magnetic particles in solutions of polymers, as a competition between the colloidal forces amid particles and their bulk transport induced by the hydrodynamic forces. For this aim, we analyse the role of different experimental parameters. Firstly, by using only solutions of a well-known anionic polymer (sodium alginate), we provoke a moderate hindering of particle movement, but keeping the liquid-like state of the samples. On the contrary, a gel-like behaviour is conferred to the samples when a cationic polymer (chitosan) is additionally added, which further reduces the particle movement. We analyse the effect of an applied magnetic field, which is opposed to particle transport by hydrodynamic forces, by inducing magnetic attraction between the particles. We perform the analysis under both stationary and oscillatory shear. We show that by using dimensionless numbers the differences between samples and experimental conditions are emphasized.Ministerio de Economía, Industria y Competitividad, MINECO and Agencia Estatal de Investigación, AEI, Spain, cofounded by Fondo Europeo de Desarrollo Regional, FEDER, European Union, project no. FIS2017-85954-R