Ladislau Vekas

Romanian Academy · Center for Fundamental and Advanced Technical Research, Tmişoara

The sealing capacity of magnetofluidic (MF) rotating seals is limited by the highest magnetization of the sealing ferrofluids (FFs) of about 1000 G (80 kA/m). A sharp, almost an order...

This chapter presents the evolution of research in Romania on the mechanics (the mechanics of rigid solids, deformable solids in elastic, elastoplastic or plastic behavior regimes, the theory of mechanical vibrations, fluid mechanics) but also closely related problems such as the theory of mechanisms, contact mechanics, construction of hydraulic eq...

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...

Drug therapy for vascular disease has been promoted to inhibit angiogenesis in atherosclerotic plaques and prevent restenosis following surgical intervention. This paper investigates the arterial depositions and distribution of PEG-functionalized magnetic nanocomposite clusters (PEG_MNCs) following local delivery in a stented artery model in a unif...

Ferrofluids investigated along for about five decades are ultrastable colloidal suspensions of magnetic nanoparticles, which manifest simultaneously fluid and magnetic properties. Their magnetically controllable and tunable feature proved to be from the beginning an extremely fertile ground for a wide range of engineering applications. More recentl...

Today, public health is one of the most important challenges in society. Cancer is the leading cause of death, so early diagnosis and localized treatments that minimize side effects are a priority. Magnetic nanoparticles have shown great potential as magnetic resonance imaging contrast agents, detection tags for in vitro biosensing, and mediators o...

High magnetization Fe3O4/OA-FeCo/Al2O3 nanocomposite magnetic clusters have been obtained by a modified oil-in-water miniemulsion method. These nanocomposite clusters dispersed in a ferrofluid carrier results in a magnetorheological fluid with improved...

Antibodies play an essential role in modern medicine for diagnostic and therapeutic applications. Even though the production of antibodies is the fastest growing pharmaceutical industry area, the cost of antibodies remains high, which limits access to antibody-based medicine both in developing and developed countries. The bottleneck and major cost...

The self-induced instabilities developed in decelerated swirling flows lead to pressure fluctuations. The swirling flows generated under variable speeds of the rotor of a swirl generator using a magneto-rheological brake are numerically and experimentally investigated. Three-dimensional turbulent flow computation is performed for several rotor spee...

Vascular stent implantation needs a rapid endothelialization to reduce morbidity and improve patient outcomes. A promising strategy to enhance the artery wall healing is to use the site-specific drug targeting technique to deliver the required medication at the site of injury. This work presents a new concept of using permanent magnet systems to gu...

The heating effect in the temperature interval of 20―70 °C on the aggregate structure in aqueous ferrofluids is analyzed basing on the data of small-angle X-ray (SAXS) and neutron (SANS) scattering. Samples prepared according to the same stabilization procedure (double-layer surfactant coating) but with different dispersed magnetic materials (magne...

Iron oxide nanoparticles are the basic components of the most promising magnetoresponsive nanoparticle systems for medical (diagnosis and therapy) and bio-related applications. Multi-core iron oxide nanoparticles with a high magnetic moment and well-defined size, shape, and functional coating are designed to fulfill the specific requirements of var...

Magnetoactive electrospun fibrous membranes consisting of polyvinylpyrrolidone (PVP), chitosan (CS) and pre‐fabricated, double‐layer oleic acid‐coated magnetite nanoparticles (OA.OA.Fe3O4) were fabricated and evaluated as new adsorbent materials for the removal and recovery of uranium (U(VI)) from aqueous solutions. The adsorption has been investig...

Structure characterizations of concentrated water-based magnetic fluids stabilized by oleic and lauric acids were done by means of small-angle neutron scattering (SANS) and complemented by dynamic light scattering and magnetization analysis. Stability of ferrofluids with time against sedimentation was concluded despite the presence of aggregates in...

In the present study, the synthesis of superparamagnetic collagen-based nanocomposite hydrogels with tunable swelling, mechanical and magnetic properties is reported. The fabrication strategy involved the preparation of pristine collagen type-I hydrogels followed by their immersion in highly stable aqueous solutions containing pre-formed double-lay...

This study reports the development of a continuous flow process enabling the synthesis of very small iron oxide nanoparticles (VSION) intended for T1-weighted magnetic resonance imaging (MRI). The influence of parameters, such as the concentration/nature of surfactants, temperature, pressure and the residence time on the thermal decomposition of iron...

Iron oxide nanoparticles are the basic components of the most promising magneto-responsive systems for nanomedicine, ranging from drug delivery and imaging to hyperthermia cancer treatment, as well as to rapid point-of-care diagnostic systems with magnetic nanoparticles. Advanced synthesis procedures of single- and multi-core iron-oxide nanoparticl...

Histamine, a biogenic amine, is abundant in fermented foods and beverages, notably wine. A high intake of this monoamine may produce adverse reactions in humans, which may be severe in individuals with a reduced capacity to catabolise extrinsic histamine. Thus, control of histamine concentration during wine production and before distribution is adv...

Blended polymer fibers based on a hydrophobic random copolymer having β-ketoester metal ion binding functionalities namely poly(methyl methacrylate)-random-poly(2-(acetoacetoxy) ethyl methacrylate) (PMMA-co-PAEMA) and the hydrophilic polyethylene oxide (PEO) were fabricated by electrospinning and further evaluated for the first time as adsorbents f...

A magneto-rheological clutch was designed and built in order to modify the speed of an axial rotor mounted in front of a centrifugal pump. The main goal by modifying the speed of the axial rotor is to increase the operating regimes with less cavitation and to uniform the flow at the inlet of the pump impeller. The magneto-rheological clutch is test...

A magneto-rheological brake (MRB) is designed and embedded in a swirl generator apparatus in order to control the runner speed. Several swirling flow configurations are obtained slowing down the runner speed. The main challenge for MRB is associated with its operation under water conditions. As a result, two magneto-rheological fluids (a convention...

Magnetic targeting is a non-invasive strategy to improve treatment efficacy for graft intimal hyperplasia (the leading cause of the arterial bypass graft failure). The present study aims are to investigate the possibility of MPs retention in the bypass graft anastomosis region where IH are developed after surgical intervention and quantify the part...

The fabrication of magnetically modified elec-trospun nanocomposite fibers based on a naturally-derived biocompatible and biodegradable polysaccharide chitosan (CS) and the hydrophilic and biocompatible poly(vinylpyrrolidone) (PVP) is reported herein. The anchoring of magnetic nanoparticles (MNPs) onto the surfaces of the electrospun PVP/CS fibers...

This paper is an in-depth analysis devoted to two basic types of water-based magnetic fluids (MFs), containing magnetite nanoparticles with electrostatic and with electro-steric stabilization, both obtained by chemical coprecipitation...

Biocompatible magnetite nanoparticles (MNPs) were prepared by post-coating the magnetic nanocores with a synthetic polymer designed specifically to shield the particles from non-specific interaction with cells. Poly(ethylene glycol) methyl ether methacrylate (PEGMA) macromonomers and acrylic acid (AA) small molecular monomers were chemically couple...

This chapter discusses the synthesis, functionalization, characterization, and imaging applications of iron-oxide-nanoparticle-based contrast agents. By reducing the size from bulk to the nanometer scale (<20 nm), ferrimagnetic iron oxide acquires a magnetic property called superparamagnetism, which is key to the potential of these particles as MRI...

Magnetoresponsive, methacrylate-based 3D polymer networks containing hydrophilic/thermoresponsive, hydrophilic/pH-responsive and hydrophobic/metal chelating functionalities and oleic acid-coated magnetite nanoparticles, have been synthesized by conventional crosslinking radical polymerization and further evaluated as adsorbents for the removal of U...

The ongoing research project SEMNAL-MRD (Seismic Protection of Engineering Structures through Dissipative Braces of Nano-Micro Magneto-Rheological Fluid Dampers), aims to develop a seismic protection system employing a semi-active structural control system. The most promising devices appear to be magneto-rheological (MR) dampers. The current paper...

Comprehensive flow and magnetization data obtained previously on the behavior of ferrofluid based magnetorheological fluids (FF-MRF) [Susan-Resiga and Vékás, Rheol. Acta 55(7), 581–595 (2016)] were correlated using a Mason number (Mn) defined for these nano-micro composite fluids and the corresponding Casson (Ca) number, instead of the Bingham numb...

Currently there is a growing demand for renewable energy in the industrialized countries. However, these sources (e.g. solar, wind) introduce a fluctuating component within the electrical grid. Therefore, the hydraulic turbines have to operate far away from the best efficiency point (BEP) covering a wide range. As a result, the self-induced instabi...

An experimental model of a magneto-rheological brake (MRB) was designed, developed and built in order to analyze in detail different brake and clutch types models. Also the test rig serves to test different MR fluids available on the market as well as several MR fluids developed and characterized in our laboratory. The preliminary test rig consists...

The impact of surfactant type on the structure organization of aqueous ferrofluids was considered based on the data of small-angle neutron scattering (SANS). The aggregates of different sizes and types were observed for magnetite magnetic nanoparticles of in heavy water stabilized by sodium oleate (SO) or dodecylbenzene sulphonic acid (DBSA). Accor...

The preparation of superparamagnetic composites obtained by CaCO3 mineralization from supersaturate aqueous solutions is presented. The preparation was conducted in the presence of oleic acid stabilized magnetite nanoparticles as a water-based magnetic fluid and insoluble templates as gel-like cross-linked polymeric beads. The presence of the magne...

We developed a new type of magnetic hybrid system with superparamagnetic behavior and high saturation magnetization, covered with poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (pAMPS) or polydopamine (pDPA) layers of controlled thickness. TEM confirms the formation of magnetic clusters with 150 nm mean diameter, highly regular shape and a ver...

Complex susceptibility measurements provide a unique and efficient means for the investigation and determination of the dynamic properties of magnetic fluids. In particular, measurement of the frequency, f(Hz), and field, H(kA/m), dependent, complex susceptibility, χ(ω, Η)= χ‘(ω, Η)- iχ“(ω, Η), of magnetic fluids has proven to be a valuable and rel...

Magnetosomes are isolated from the Magnetospirillum magneticum strain AMB-1 bacteria. Two samples are compared: magnetosomes normally prepared of a 'standard' length and magnetosomes of a short length. Chains of magnetosomes are shortened by mechanical modification (cleavage) by means of sonication treatment. They represent a new geometry of magnet...

The magnetorheological behavior of three sets of ferrofluid-based magnetorheological (MR) fluids is investigated to determine the dependence of the static and dynamic yield stresses, as well as of the magnetoviscous effect on the volume fraction of magnetite nanoparticles φ and of the added Fe particles Φ Fe , at different values of the magnetic in...

A quantitative treatment of the effects of magnetic mutual interactions on the specific absorption rate of a superparamagnetic system of iron oxide nanoparticles coated with oleic acid is reported. The nanoparticle concentration of the considered ferrofluid samples varied from a very low (0.005) to a medium (0.16) value of the volume fraction, wher...

The study on radiation stability of some magnetic liquids used in nuclear power plants for the restriction of loss coolant is presented. The oxidation of organic fraction which is subjected to radiochemical degradation is investigated by nonisothermal chemiluminescence, which depicts the evolution of accelerated ageing as the temperature increase....

The paper focuses on numerical analysis of temperature field into a magneto-rheological break. The magneto-rheological fluid is used for a brake operated at different speeds. The magneto-rheological brake application was developed due to the magnetic control and fast response. The two dimensional axi-symmetric computational domain corresponds to th...

In this paper, static magnetic properties and magnetorheological behavior of a set of 12 nano-micro composite magnetic fluids (CMFs) were studied. The samples with a ferromagnetic particle volume fraction ranging in a large interval φFe=(1÷44)% were prepared by adding carbonyl iron powder in a highly concentrated transformer oil-based ferrofluid (F...

A review of neutron scattering researches of various magnetic fluids (ferrofluids) is made. Advantages and disadvantages of other complementary methods for the structure characterization of ferrofluids are discussed. The small-angle neutron scattering (SANS) method with a wavelength of 0.1–1 nm is a classic example of applying radiation to the dete...

Laser pyrolysis was employed to synthesize iron-based magnetic nanocomposites from fixed Fe(CO)5 and various CS2 vapor flows by using C2H4 as sensitizer. The resulted nanopowders were composed from a mixture of iron-containing phases: metallic, carbides, oxide (maghemite) and sulfide (pyrrhotite). The γFe2O3 was formed after post-synthesis air expo...

γFe2O3-based nanoparticles were synthesized by laser pyrolysis using various optimized Fe(CO)5, O2 and C2H4 flow ratios in the reactive mixture, and different laser power values. Depending on particular conditions, two different iron oxide-based nanoparticles (MNPs) were synthesized, with a hydrophilic or hydrophobic behavior, both presenting a hig...

The study on radiation stability of some magnetic liquids used in nuclear power plants for the restriction of loss coolant is presented. The oxidation of organic fraction which is subjected to radiochemical degradation is investigated by nonisothermal chemiluminescence, which depicts the evolution of accelerated ageing as the temperature increase....

We report the synthesis and characterization of new hybrid materials based on conducting polypyrrole (PPY) and multi wall carbon nanotubes (MWCNTs). MWCNTs were prepared by spray-pyrolysis of liquid hydrocarbon-ferrocene solution in an Ar atmosphere. The composites (PPY-CNT) were obtained by in-situ chemical oxidative polymerization of pyrrole in a...

Photothermoelectric (PTE) calorimetry was applied for the first time for thermal characterization of liquids. Both back and front detection configurations, together with the thermal-wave resonator cavity (TWRC) scanning procedure, have been used in order to measure the thermal diffusivity and thermal effusivity of a particular magnetic nanofluid: c...

Magnetoactive nanocomposite fibers, based on poly(ethylene oxide) (PEO), poly(L-lactide) (PLLA) and pre-formed oleic acid-coated magnetite nanoparticles (OA·Fe3O4), were fabricated by electrospinning and evaluated for the first time as substrates for the adsorption of N-methylated diaminotriphenylmethane dye (malachite green oxalate, MG) from aqueo...

The decelerated swirling flow in the draft tube cone of hydraulic turbines (especially turbines with fixed blades) is responsible for self-induced instabilities which generates pressure pulsations that hinder the turbine operation. An experimental test rig was developed in order to investigate the flow instabilities. A new method was implemented to...

For specific applications in the field of high gradient magnetic separation of biomaterials, magnetic nanoparticle clusters of controlled size and high magnetic moment in an external magnetic field are of particular interest. We report the synthesis and characterization of magnetic microgels designed for magnetic separation purposes, as well as the...

The building blocks for the fabrication of biocompatible magnetoresponsive carriers are the subdomain magnetite nanoparticles surface coated by biocompatible molecular layers which ensure their stabilization and dispersion in an appropriate carrier liquid, in order to obtain stable magnetic nanofluids that are the primary materials for the envisage...

In this paper, the magnetorheological (MR) and magnetoviscous properties of ferrofluid-based iron particle suspensions were investigated. The 2.1-µm mean size Fe particles were dispersed in high-concentration transformer oil-based ferrofluid, the iron particle volume fraction in the resulting nano-micro composite magnetorheological fluid samples va...

A new and facile synthesis approach employed for the fabrication of multiresponsive polymer conetworks characterized by predefined architecture and composition is described for the first time. The presented methodology involves the crosslinking of well-defined 2-(dimethylamino)ethyl methacrylate (DMAEMA) homopolymers and polyDMAEMA-containing diblo...

X-ray microcomputed tomography was used in a three-dimensional investigation of the microstructure of suspensions of multi-domain soft iron particles in magnetic nanofluids. The measurements were performed using two different approaches: with the sample kept frozen, and with the sample under the effect of an external magnetic field. Results show th...

Magnetite nanoparticles (MNP) were synthesized and stabilized with carboxylated compounds citric acid – CA, poly(acrylic acid) – PAA, poly(acrylic acid-co-maleic acid) – PAM, humic acid – HA and gallic acid – GA (polymerizing in situ on the surface). Adsorption isotherms and bonding feature were determined and used to explain the changes in charge...

The fabrication of magnetoactive fibrous nanocomposite membranes based on poly(vinyl pyrrolidone) (PVP), poly(L-lactide) (PLLA) and pre-formed oleic acid coated magnetite nanoparticles (OA Fe3O4) is presented. The aforementioned materials have been prepared by means of the electrospinning technique following a single-step fabrication process. The P...

Results of the structure and interparticle interaction investigations of polar magnetic fluid with different content of magnetite, which are obtained by small-angle neutron scattering(SANS) are presented in the work. The experiment was performed on small-angle scattering spectrometer YuMO at the Pulsed Reactor IBR-2 in the Joint Institute for Nucle...

The fabrication of electrospun magnetoactive fibrous nanocomposite membranes based on the water soluble and biocompatible poly(ethylene oxide) (PEO), the biocompatible and biodegradable poly(L-lactide) (PLLA) and pre-formed oleic acid-coated magnetite nanoparticles (OA.Fe3O4) is reported. Visualization of the membranes by electron microscopy techni...

We report the synthesis and characterization of magnetic nanogels based on magnetite nanoparticles sterically stabilized by double layer oleic acid in water carrier and chemically cross linked poly (N-isopropylacril amide) (pNIPA) and poly (acrylic acid) (pAAc). In this structure the magnetite nanoparticles are attached to the flexible network chai...

Five types of magnetic nanofluids, based on Fe3O4 nanoparticles with water as the carrier liquid, were investigated by using the two photopyroelectric (PPE) detection configurations (back (BPPE) and front (FPPE)), together with the thermal-wave resonator cavity (TWRC) technique as the scanning procedure. The difference between the nanofluids was th...