0000000000875315
AUTHOR
Guntars Kitenbergs
Low-Cost Solution for Magnetic Field Mapping Device
Distribution of magnetic field around different magnetic objects is important for various applications of magnetic materials. Field distribution can be measured with a 3-axis Hall probe sensor, which is moved around the sample. There are excellent systems available in market for this purpose for example, magnetic field mapper MMS-1A-RS from SENIS AG. However, these systems are quite expensive, starting from 25000=C. Here we demonstrate how a simple automated magnetic field mapper can be made from common parts found in laboratories, test it to verify accuracy, compare results with numerical simulations and discuss the benefits of this low-cost alternative.
Deformation of flexible ferromagnetic filaments under a rotating magnetic field
Research on magnetic particles dispersed in a fluid medium, actuated by a rotating magnetic field, is becoming increasingly active for both lab-on-chip and bio-sensing applications. In this study, we experimentally investigate the behaviour of ferromagnetic filaments in a rotating field. Filaments are synthesized by linking micron-sized ferromagnetic particles with DNA strands. The experiments were conducted under different magnetic field strengths, frequencies and filament sizes, and deformation of the filaments was registered via microscope and camera. The results obtained showed that the body deformation is larger for longer filaments and higher frequencies and lower for larger magnetic …
Magnetic field driven micro-convection in the Hele-Shaw cell: the Brinkman model and its comparison with experiment
International audience; The micro-convection caused by the ponderomotive forces of the self-magnetic field in a magnetic fluid is studied here both numerically and experimentally. The theoretical approach based on the general Brinkman model substantially improves the description with respect to the previously proposed Darcy model. The predictions of both models are here compared to finely controlled experiments. The Brinkman model, in contrast to the Darcy model, allows us to describe the formation of mushrooms on the plumes of the micro-convective flow and the width of the fingers. In the Brinkman approach, excellent quantitative agreement is also obtained for the finger velocity dynamics …
Gravity effects on mixing with magnetic micro-convection in microfluidics.
Mixing remains an important problem for development of successful microfluidic and lab-on-a-chip devices, where simple and predictable systems are particularly interesting. One is magnetic micro-convection, an instability happening on the interface of miscible magnetic and non-magnetic fluids in a Hele-Shaw cell under applied field. Previous work proved that Brinkman model quantitatively explains the experiments. However, a gravity caused convective motion complicated the tests. Here we first improve the experimental system to exclude the gravitational convective motion. Afterwards, we observe and quantify how gravity and laminar flow play an important role in stabilizing the perturbations …
Rotating hematite cube chains
Recently a two-dimensional chiral fluid was experimentally demonstrated. It was obtained from cubic-shaped hematite colloidal particles placed in a rotating magnetic field. Here we look at building blocks of that fluid, by analyzing short hematite chain behavior in a rotating magnetic field. We find equilibrium structures of chains in static magnetic fields and observe chain dynamics in rotating magnetic fields. We find and experimentally verify that there are three planar motion regimes and one where the cube chain goes out of the plane of the rotating magnetic field. In this regime we observe interesting dynamics -- the chain rotates slower than the rotating magnetic field. In order to ca…
Gelation of semiflexible polyelectrolytes by multivalent counterions
Filamentous polyelectrolytes in aqueous solution aggregate into bundles by interactions with multivalent counterions. These effects are well documented by experiment and theory. Theories also predict a gel phase in isotropic rodlike polyelectrolyte solutions caused by multivalent counterion concentrations much lower than those required for filament bundling. We report here the gelation of Pf1 virus, a model semiflexible polyelectrolyte, by the counterions Mg(2+), Mn(2+) and spermine(4+). Gelation can occur at 0.04% Pf1 volume fraction, which is far below the isotropic-nematic transition of 0.7% for Pf1 in monovalent salt. Unlike strongly crosslinked gels of semiflexible polymers, which stif…
Instabilités hydrodynamiques de fluides magnétiques en écoulements microfluidiques
Advisors: Prof. Andrejs Cēbers (University of Latvia) & Prof. Régine Perzynski (University of Pierre and Marie Curie)
Rivalry of diffusion, external field and gravity in micro-convection of magnetic colloids
Magnetic fields and magnetic materials have promising microfluidic applications. For example, magnetic micro-convection can enhance mixing considerably. However, previous studies have not explained increased effective diffusion during this phenomenon. Here we show that enhanced interface smearing comes from a gravity induced convective motion within a thin microfluidic channel, caused by a small density difference between miscible magnetic and non-magnetic fluids. This motion resembles diffusive behavior and can be described with an effective diffusion coefficient. We explain this with a theoretical model, based on a dimensionless gravitational Rayleigh number, and verify it by numerical si…
3D motion of flexible ferromagnetic filaments under a rotating magnetic field.
Ferromagnetic filaments in a rotating magnetic field are studied both numerically and experimentally. The filaments are made from micron-sized ferromagnetic particles linked with DNA strands. It is found that at low frequencies of the rotating field a filament rotates synchronously with the field and beyond a critical frequency it undergoes a transition to a three dimensional regime. In this regime the tips of the filament rotate synchronously with the field on circular trajectories in the plane parallel to the plane of the rotating field. The characteristics of this motion found numerically match the experimental data and allow us to obtain the physical properties of such filaments. We als…
Magnetic Soft Matter: Book of Abstracts, 79th Scientific Conference of the University of Latvia, February 11, 2021
Seminar chair is Professor Andrejs Cēbers. Seminar organizing committee includes Dārta Antāne, Ivars Driķis and Guntars Kitenbergs.
Kustības magnētiskajā laukā reģistrācija un digitālā apstrāde
Darbā aprakstīta metode atsevišķu objektu magnētisko momentu noteikšanai, analizējot vides siltumfluktuāciju ietekmi uz to magnetoforētisko kustību. Izveidota magnetoforēzes iekārta un atbilstošs attēlu apstrādes algoritms. Parādīts, ka veicot magnētisku daļiņu kustības videoierakstu, iespējams noteikt to kustības trajektorijas un vidējos ātrumus. Vidējo ātrumu sadalījums katrai daļiņai ir atkarīgs no vides siltumfluktuācijām un var tikt aprakstīts ar teorētisku sakarību. No tās tika atrastas difūzijas koeficienta un vidējā kustības ātruma vērtības, kas ļauj aprēķināt objekta magnētisko momentu. Metode pārbaudīta, nosakot komerciālu magnētisku daļiņu magnētisko momentu dispersiju. Demonstrē…
Latvian-Brazilian meeting on Active and Soft Matter Physics: Book of Abstracts, Thursday, 3 February 2022, 15:00, Online
This abstract book is made for the Latvian-Brazilian meeting on Active and Soft Matter Physics, held on February 3, 2022. It was organized by the MMML lab (Lab of Magnetic Soft Materials) of the University of Latvia together with the Condensed Matter Physics Group of the Federal University of Ceará (Fortaleza, Brazil) as a part of the 80th International Scientific Conference of the University of Latvia. It includes topical contributions from researchers working on active and soft matter physics at both research groups.
Magnetic micro-droplet in rotating field: numerical simulation and comparison with experiment
Magnetic droplets obtained by induced phase separation in a magnetic colloid show a large variety of shapes when exposed to an external field. However, the description of shapes is often limited. Here we formulate an algorithm based on three dimensional boundary-integral equations for strongly magnetic droplets in a high-frequency rotating magnetic field, allowing us to find their figures of equilibrium in three dimensions. The algorithm is justified by a series of comparisons with known analytical results. We compare the calculated equilibrium shapes with experimental observations and find a good agreement. The main features of these observations are the oblate-prolate transition, the flat…
Colloidal nanoparticle sorting and ordering on anodic alumina patterned surfaces using templated capillary force assembly
Abstract A new, robust technique of size-selective nanoparticle ordering on porous anodized aluminum oxide (PAAO) templates is presented. Simultaneous particle sorting and array formation is achieved for the first time using a polydisperse suspension of irregularly shaped diamond nanocrystals. The array parameters can be tuned through a balance of evaporation driven particle flux, capillary, electrostatic, and adhesion forces, which are influenced by the asperities of the surface during the capillary and convective assembly dip-coating process. The resulting structures are dense (lower limit approximately 50 nm center separation), isolated (non-touching) nanoparticle arrays with a size dist…
Magnetic field driven micro-convection in the Hele-Shaw cell
AbstractMicro-convection caused by ponderomotive forces of the self-magnetic field of a magnetic fluid in the Hele-Shaw cell under the action of a vertical homogeneous magnetic field is studied both experimentally and numerically. It is shown that a non-potential magnetic force at magnetic Rayleigh numbers greater than the critical value causes fingering at the interface between the miscible magnetic and non-magnetic fluids. The threshold value of the magnetic Rayleigh number depends on the smearing of the interface between fluids. Fingering with its subsequent decay due to diffusion of particles significantly increases the mixing at the interface. Velocity and vorticity fields at fingering…
Swarming of micron-sized hematite cubes in a rotating magnetic field -- Experiments
Energy input by under-field rotation of particles drives the systems to emergent non-equilibrium states. Here we investigate the suspension of rotating magnetic cubes. Micron-sized hematite cubes are synthesized and observed microscopically. When exposed to a rotating magnetic field, they form rotating swarms that interact with each other like liquid droplets. We describe the swarming behaviour and its limits and characterize swarm size and angular velocity dependence on magnetic field strength and frequency. A quantitative agreement with a theoretical model is found for the angular velocity of swarms as a function of field frequency. It is interesting to note that hematite particles with p…
Relating magnetization, structure and rheology in ferrofluids with multi-core magnetic nanoparticles
Abstract Due to their magnetic moments solubilized magnetic nanoparticles are able to spontaneously assemble into dipolar mesostructures, which affect the flow behavior. Multi-core magnetic nanoparticles developed for biomedical applications have enhanced magnetic properties and show significant magnetoviscous effect, but the quantitative interpretation of this phenomenon is incomplete. We apply rheological measurements, magnetic granulometry and dimensional scaling to show the existence of a master curve for magnetorheology of these materials. Using the developed approach the magnetoviscous effect can now be interpreted in a unified way within the stochastic chain model.
Magnetic particle mixing with magnetic micro-convection for microfluidics
International audience; In this paper we discuss the magnetic micro-convection phenomenon as a tool for mixing enhancement in microfluidics systems in cases when one of the mis-cible fluids is a magnetic particle colloid. A system of a water-based magnetic fluid and water is investigated experimentally under homogeneous magnetic field in a Hele-Shaw cell. Subsequent image analysis both qualitatively and quan-titatively reveals the high enhancement of mixing efficiency provided by this method. The mixing efficiency dependence on the magnetic field and the phys-ical limits is discussed. A suitable model for a continuous-flow microfluidics setup for mixing with magnetic micro-convection is als…
Deformation of flexible ferromagnetic filaments under a rotating magnetic field
This repository contains experimental data and images related to the publication: A. Zaben, G. Kitenbergs, A. Cēbers (2020) Deformation of flexible ferromagnetic filaments under a rotating magnetic field. Journal of Magnetism and Magnetic Materials, 499, 166233 https://doi.org/10.1016/j.jmmm.2019.166233 / https://arxiv.org/abs/1908.02604. Excel files are results named corresponding to figure number in the publication. Root file '1' is for experimental images used for Fig.3, 4 and 5; where either the length is constant having file names as the value of the field strength or named with length values with fixed field strength for different frequencies. The images are named as …
3D motion of flexible ferromagnetic filaments under rotating magnetic field
This repository contains experimental data and numerical results related to the publication: A. Zaben, G. Kitenbergs, A. Cēbers (2020), 3D motion of flexible ferromagnetic filaments under rotating magnetic field. Soft Matter, https://doi.org/10.1039/D0SM00403K / https://arxiv.org/abs/2003.03737. Figs_data.xlsx contains the data presented in the figures. Experimental_Data.rar contains experimental images used to obtain the results for Fig. 3 and 9. The files are named with the operating frequency, field strength and filament length. Numerical.rar contains numerical results used in Fig.6, 8 and 9. The files are named with Cm values. The results are in .dat files named with Cm values follo…