Jose R Morillas

University of Granada | UGR · Department of Applied Physics

We design, fabricate, and test a double-gap bicone magnetorheological (MR) device to measure steady shear rheological properties of MR fluids under saturating magnetic fields (i.e., large enough to saturate the MR fluids). The device is optimized using finite element method and computational fluid dynamics simulations so that homogeneous, saturatin...

Magnetic field generators with the ability to create well-controlled dynamic fields in arbitrary directions are an essential tool to investigate magnetic soft matter and to drive (sub)micrometer structures to targeted locations. In this article we present the design and performance of a triaxial generator based on three fractal capacitor banks that...

In order to generate homogeneous magnetophoretic forces, current magnetic tweezer devices operate placing electromagnetic inductors far enough from the sample. Consequently, high-power supplies are needed to reach sufficiently large forces. We demonstrate that both magnetophoretic force magnitude and homogeneity can be increased at will in this kin...

Magnetically responsive soft matter is a colloidal model system where interparticle interactions can be tuned through external magnetic fields. Covering the most recent literature in the field, with special emphasis on the physical mechanisms behind their rheological behaviour, this book aims to demonstrate the controllability of soft matter throug...

Shear thinning fluids represent a class of non-Newtonian media characterized by a decrease of the apparent viscosity when increasing the shear rate. Here we experimentally demonstrate a deterministic ratchet effect in such media that enables directed transport of microscopic particles under a square-wave magnetic force. The applied modulation is de...

The postyield rheological regime is investigated in sheared magnetic field-responsive composites (i.e. carbonyl iron based magnetorheological fluids). When subjected to uniaxial DC fields, high-speed videomicroscopy techniques and dedicated image analysis tools demonstrate that dispersed magnetic microparticles self-assemble to form concentric laye...

A new formulation is proposed to lubricate tribopairs in extreme conditions where the amount of lubricant is small and the lubricating region highly confined. It is composed of non-magnetic solid lubricants dispersed in an oil-based ferrofluid. When this inverse ferrofluid (IFF) is magnetically activated, the lubricant particles are subjected to ma...

We propose three different techniques to synthesize anisotropic magnetic supraparticles for their incorporation in the formulation of magnetorheological fluids with novel potential applications. The techniques include microtransfer molding, electrodeposition and microfluidic flow-focusing devices. Although the yield of these methods is not large, w...

Hydrogels with self-healing properties constitute one of the most versatile three-dimensional (3D) materials for application in biomedicine due to the possibility of modulating their characteristics and incorporating specific elements such as magnetic particles (MPs). Herein, we describe a simple approach on the fabrication of self-healing magnetic...

Magnetic Soft Matter is a rapidly evolving discipline with fundamental and practical interest. This is due to the fact that its physical properties can be easily controlled through external magnetic fields. In this review paper, we revisit the most recent progress in the field (since 2010) emphasizing the rheological properties of these fascinating...

The underlying physics behind magnetorheological fluids is described under the presence of uniaxial DC fields and steady simple shear. A universal master curve exists in terms of two dimensionless numbers (the particle volume fraction and the Mason number). Especial emphasis is given to the particle concentration dependence.

Magnetic colloids were formulated by dispersion of magnetic oxide spheres in water. Their rheological behavior was investigated for a wide range of particle diameters covering in detail the magnetic single-multidomain transition and therefore spanning the gap between ferrofluids and conventional magnetorheological fluids. The magnetoviscous effect...

Understanding magnetorheology in saturating fields is crucial for success in high torque applications. In this paper we use numerical computations, analytical developments, and experimental data (using a double-gap magnetocell) to study the saturation behavior of model magnetorheological fluids for different particle loadings. Numerical calculation...

The yielding behavior of magnetorheological fluids is revisited through the use of finite element method calculations on model structures and carefully conducted experiments in a magnetorheometer. Model structures investigated in this work are monoclinic lattices with simple and body centered bases. From the simulation point of view we emphasize th...

Undoubtedly, the yield stress is the most relevant rheological property of a magnetorheological (MR) fluid. However, available analytical and simulation methodologies to compute the magnetostatic interparticle interactions that govern the yield stress, fail at large particle concentrations and large strain levels. In this communication we propose a...

A double-gap magnetorheological (MR) cell is designed, constructed, and validated using finite element method magnetostatics simulations, computational fluid dynamics calculations, and experimental data with Newtonian fluids and conventional MR fluids for a range of particle concentrations and external magnetic field strengths. This new cell is a g...

In this manuscript we investigate the shear rheology, sedimentation stability and redispersibility characteristics of bimodal MR fluids with a Large-to-Small size ratio σ_L/σ_S≈100 where the small-size population of particles is in the single- multidomain limit (σ_S≈100 nm) to promote the formation of core-shell supraparticles (i.e. large particles...

We demonstrate a new route to enhance the magnetorheological effect using bimodal suspensions in the single-multidomain limit. Experimental results are satisfactorily compared to 3D finite element method simulations. The physical reason behind this enhancement is the coating of the larger particles by the smaller ones due to the remnant magnetizati...

A new kind of magnetorheological fluid is proposed that exhibits both enhanced magnetorheological effect and kinetic stability against sedimentation. It includes the presence of small amounts of an emulsified aqueous ferrofluid as a third phase in a conventional oil-based magnetorheological fluid prepared by the dispersion of carbonyl iron micropar...

We investigate the (irreversible) two-dimensional aggregation kinetics of dilute non-Brownian magnetic suspensions in rectangular microchannels using video-microscopy, image analysis and particle-level dynamics simulations. Special emphasis is given to carbonyl iron suspensions that are of interest in the formulation of magnetorheological fluids. T...

This work reports an investigation into the effect of 1-octanol concentration in the formulation of concentrated polyalphaolefin-based magnetorheological fluids. Special emphasis is paid to the understanding of their kinetic stability and redispersibility characteristics in the 'off-state' (absence of magnetic field). Techniques employed involve li...

This work proposes the use of quartz crystal microbalances (QCMs) as a method to analyze and characterize magnetorheological (MR) fluids. QCM devices are sensitive to changes in mass, surface interactions, and viscoelastic properties of the medium contacting its surface. These features make the QCM suitable to study MR fluids and their response to...

We investigate the influence of the aspect ratio of the dispersed particles in magnetorheology. Two systems are studied: conventional magnetorheological fluids prepared by dispersion of nickel nanowires, and inverse ferrofluids prepared by dispersion of glass fibers in a ferrofluid. In both cases the apparent yield stress is found to increase with...

We report a systematic experimental investigation on the use of nanofibers to enhance the magnetorheological (MR) effect in conventional (microsphere-based) MR fluids formulated in polyalphaolefin oil/1-octanol. Two kinds of nanofibers are employed that have very similar morphology but very different magnetic properties. On the one hand we use non-...