Oleic Acid Monolayer Research Articles

Experimental and computational insights into self-assembly sodium oleate on anodized aluminum interface in electric field

Electrochemical etching method has been used to construct anode aluminum foils with large surface area for electrolytic capacitor application. The applied current concentrated on surface defects would cause excessive corrosion of aluminum substrate and accelerate the initiation of merged tunnels. Self-assembly treatment with sodium oleate presents considerable improvement on optimization of size and structure of etched tunnels. Experimentally, aluminum foils with high etched tunnel density nearly 1.5027 × 107 cm−2 could be prepared after 0.10 mmol L−1 sodium oleate treatment. Theoretically, molecular dynamic and quantum chemistry calculations reveal the self-assembly process of sodium oleate in forms of oleic acid on Al (100) facet. The results indicate that the oleic acid monolayer will form at molecular density nearly 0.855, 0.847 and 0.844 mol. nm−2 as electric field E equal 0, 0.10 V Å−1 and 1.00 V Å−1, respectively. Based on the calculations of surface coverage in electric field conditions, experimental adsorption isotherm has been corrected to determine the optimal concentration of self-assembly composition.

Hydrophobic magnetic bilayer micro-particles from OA@Lignin@Fe3O4 for high-efficient oil adsorption

Marine oil or heavy oil spills occur frequently, causing pollution and endangering lives in marine, sea and river, even the soil. In this paper, a magnetic, hydrophobic and bilayer composite oleic acid@Lignin@Fe3O4 was synthesized by a simple method to remove oil contaminants floating on water. SEM, TEM, FT-IR, TGA, XRD, VSM and CA analyses were used to examine its structures, chemical composition and performance. With an oleic acid (OA) monolayer on surface, OA@Lignin@Fe3O4 microspheres showed excellent oil adsorption performance with quick adsorption equilibrium of 10 s, good adsorption capacity of 3.07, 3.52, 3.04 and 2.53 times its original weight for vacuum pump oil, soybean oil, dimethicone and kerosene, respectively. Furthermore, the OA@Lignin@Fe3O4 could be guided to collect oil droplets and separated from water under a magnetic field. Meanwhile, the OA@Lignin@Fe3O4 exhibited high cycle performance, which maintained high oil adsorption capacity after 5 recycles. Therefore, the OA@Lignin@Fe3O4 is believed to a promising adsorbent for oil removal and provides a novel avenue for multifunctional adsorbents in water treatment.

Surfactant Driven Marangoni Spreading in the Presence of Predeposited Insoluble Surfactant Monolayers.

When an insoluble surfactant is deposited on the surface of a thin fluid film, stresses induced by surface tension gradients drive Marangoni spreading across the subphase surface. The presence of a predeposited layer of an insoluble surfactant alters that spreading. In this study, the fluid film was aqueous, the predeposited insoluble surfactant was dipalmitoylphosphatidylcholine (DPPC), and the deposited insoluble surfactant was oleic acid. An optical density-based method was used to measure subphase surface distortion, called the Marangoni ridge, associated with propagation of the spreading front. The movement of the Marangoni ridge was correlated with movement of surface tracer particles that indicated both the boundary between the two surfactant layers and the surface fluid velocities. As the deposited oleic acid monolayer spread, it compressed the predeposited DPPC monolayer. During spreading, the surface tension gradient extended into the predeposited monolayer, which was compressed nonuniformly, from the deposited monolayer. The spreading was so rapid that the compressed predeposited surfactant could not have been in quasi-equilibrium states during the spreading. As the initial concentrations of the predeposited surfactant were increased, the shape of the Marangoni ridge deformed. When the initial concentration of the predeposited surfactant reached about 70 A2/molecule, there was no longer a Marangoni ridge but rather a broadly distributed excess of fluid above the initial fluid height. The nonuniform compression of the annulus of the predeposited monolayer also caused tangential motion ahead of both the Marangoni ridge and the boundary between the two monolayers. Spreading ceased when the two monolayers reached the same final surface tension. The final area per molecule of the DPPC monolayer matched that expected from the equilibrium DPPC isotherm at the same final surface tension. Thus, at the end of spreading, there was a simple surface tension balance between the two distinct monolayers.

Evidence for Phospholipids on the Surface of Human Tears.

PurposeThe structure of tears has been theoretically considered three tiers with lipids at the air interface, aqueous and proteins in the subphase, and anchored mucins on the corneal epithelial surface. While many lipid and protein species have been identified in tears by mass spectrometry, the localization of the major components within the tear film structure remains speculative. The most controversial components are phospholipids. Although surface active, phospholipids have been presumed to be bound entirely to protein in the aqueous portion of tears or reside at the aqueous-lipid interface. Herein, the possibility that phospholipids are adsorbed at the air-surface interface of tears is interrogated.MethodsPolarization-modulated Fourier transform infrared reflective absorption spectroscopy (PM-IRRAS) was used to study the presence of phosphate signals at the tear surface. In order to constrain the depth of signal detection to the surface, an extreme grazing angle of incident radiation was employed. Nulling ellipsometry was used to confirm the presence of monolayers and surface thicknesses when surface active reagents were added to solutions.ResultsSurface selection of PM-IRRAS was demonstrated by suppression of water and phosphate signals in buffers with monolayers of oleic acid. Phosphate signals were shown to reflect relative concentrations. Absorption peaks attributable to phospholipids were detected by PM-IRRAS on the human tear film surface and were augmented by the addition of phospholipid.ConclusionsThe data provide strong evidence that phospholipids are present at the surface of tears.

Interfacial complex of α-lactalbumin with oleic acid: effect of protein concentration and PM-IRRAS study

We used the Langmuir technique to investigate the binding of the bovine α-lactalbumin (BLA III) to the oleic acid (OA) monolayer in gastric conditions (pH 2.0 and 36.6 °C). Both substances are components of the BAMLET complex, which is beneficial to human health. The monolayer studies have been completed with BAM imaging and PM-IRRAS spectra. This paper explores the interfacial behavior of the lipid monolayer in the presence of the protein. It proves that the higher the concentration of protein in the subphase, the higher the increase in the relative surface pressure of the OA monolayer is, until the additional amount of protein affects the maximmum film response. We also discussed the MIP (maximum insertion pressure) value and analyzed the infrared spectra to prove that BLA III interacts with OA at the interface. We focused on the kinetics of the interaction between these components. We noticed that after protein adsorption at the interface (which rate depends on BLA III concentration), the protein penetrates the lipid monolayer, followed by film rearrangement (the protein forces on fatty acid molecules to change their orientation) until finally a stable lipid-protein complex is formed at the air-water interface. This multi-stage process is relevant to the course of a relaxation curve, which demonstrates the monolayer response on protein injection. This paper explores the physicochemical phenomena which fully recognized may open the door to numerous applications of these lipid-protein system.

Homogeneously dispersed composites of hydroxyapatite nanorods and poly(lactic acid) and their mechanical properties and crystallization behavior

Aiming to disperse HA nanocrystals in a polymer matrix homogenously, uniform oil-soluble HA nanorods were synthesized via an oleic acid (OA)-assisted mixed-solvent thermal method, and then poly(lactic acid) (PLA)/HA nanorods nanocomposites were fabricated by using a solution method. The HA nanorods with an OA monolayer on the surface dispersed homogeneously in organic solvents and the dispersion in polymer solution was transparent and colloidally stable. TEM images showed that HA nanorods dispersed as single particles without aggregation in PLA matrix. The elongation at break of the composites increased from 4.24% to 8.79% by adding HA nanorods, whereas the tensile strength and Young's modulus were largely unchanged. HA nanorods accelerated evidently the PLA crystallization rate even at a low HA loading and induced a transition to an ordered crystalline morphology confirmed via non-iso/isothermal crystallization, the spherulitic morphology, calculations and wide-angle X-ray diffraction during heating and cooling cycles.

The reaction of oleic acid monolayers with gas-phase ozone at the air water interface: the effect of sub-phase viscosity, and inert secondary components.

Organic films that form on atmospheric particulate matter change the optical and cloud condensation nucleation properties of the particulate matter and consequently have implications for modern climate and climate models. The organic films are subject to attack from gas-phase oxidants present in ambient air. Here we revisit in greater detail the oxidation of a monolayer of oleic acid by gas-phase ozone at the air-water interface as this provides a model system for the oxidation reactions that occur at the air-water interface of aqueous atmospheric aerosol. Experiments were performed on monolayers of oleic acid at the air-liquid interface at atmospherically relevant ozone concentrations to investigate if the viscosity of the sub-phase influences the rate of the reaction and to determine the effect of the presence of a second component within the monolayer, stearic acid, which is generally considered to be non-reactive towards ozone, on the reaction kinetics as determined by neutron reflectometry measurements. Atmospheric aerosol can be extremely viscous. The kinetics of the reaction were found to be independent of the viscosity of the sub-phase below the monolayer over a range of moderate viscosities, , demonstrating no involvement of aqueous sub-phase oxidants in the rate determining step. The kinetics of oxidation of monolayers of pure oleic acid were found to depend on the surface coverage with different behaviour observed above and below a surface coverage of oleic acid of ∼1 × 1018 molecule m-2. Atmospheric aerosol are typically complex mixtures, and the presence of an additional compound in the monolayer that is inert to direct ozone oxidation, stearic acid, did not significantly change the reaction kinetics. It is demonstrated that oleic acid monolayers at the air-water interface do not leave any detectable material at the air-water interface, contradicting the previous work published in this journal which the authors now believe to be erroneous. The combined results presented here indicate that the kinetics, and thus the atmospheric chemical lifetime for unsaturated surface active materials at the air-water interface to loss by reaction with gas-phase ozone, can be considered to be independent of other materials present at either the air-water interface or in the aqueous sub-phase.

Lipid-Protein Interactions in Langmuir Monolayers under Dynamically Varied Conditions.

In the Langmuir monolayer technique, a single layer of molecules is formed on a water subphase. This approach was used to mimic the antitumoricidal lipid-protein complex of oleic acid and bovine α-lactalbumin called the BAMLET complex. Our previous studies have shown that at the interface, the BAMLET complex is stabilized by the hydrophobic forces supported by the hydrogen bonds. This study provides an insight into the influence of calcium ions and the experimental conditions (temperature and subphase pH) on the stability of the complex at the interface. The Langmuir technique was expanded using a dosing pump to exchange the subphase and deliver additional substances to the system. We investigated the interactions between oleic acid monolayer and α-lactalbumin in the presence of Ca2+ in the bulk and the effect of varied experimental conditions on the complex stability. The role of calcium ions in this system is important because (in addition to low pH and relatively high temperature) it affects the conformational changes within the protein molecule and facilitates the transition of α-lactalbumin into the molten globule state. A partially unfolded state is required to form the BAMLET complex. We found that the mixed monolayer spread at the interface is stable despite drastic changes in the process conditions and remains stable even after the subphase exchange. This study of molecular interactions explored by the Langmuir technique with peristaltic pump enabled to understand the role of Ca2+ in BAMLET complex formation.

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air–aqueous interface

Abstract. Water-soluble brown carbon in the aqueous core of aerosol may play a role in the photochemical aging of organic film on the aerosol surface. To better understand the reactivity and photochemical aging processes of organic coating on the aqueous aerosol surface, we have simulated the photosensitized reaction of organic films made of several long-chain fatty acids in a Langmuir trough in the presence or absence of irradiation. Several chemicals (imidazole-2-carboxaldehyde and humic acid), PM2.5 samples collected from the field, and secondary organic aerosol samples generated from a simulation chamber were used as photosensitizers to be involved in the photochemistry of the organic films. Stearic acid, elaidic acid, oleic acid, and two different phospholipids with the same carbon chain length and different degrees of saturation, i.e. 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC), were chosen as the common organic film-forming species in this analysis. The double bond (trans and cis) in unsaturated organic compounds has an effect on the surface area of the organic monolayer. The oleic acid (OA) monolayer possessing a cis double bond in an alkyl chain is more expanded than elaidic acid (EA) monolayers on artificial seawater that contain a photosensitizer. Monitoring the change in the relative area of DOPC monolayers has shown that DOPC does not react with photosensitizers under dark conditions. Instead, the photochemical reaction initiated by the excited photosensitizer and molecular oxygen can generate new unsaturated products in the DOPC monolayers, accompanied by an increase in the molecular area. The DSPC monolayers did not yield any photochemical oxidized products under the same conditions. The spectra measured with polarization modulation-infrared reflection–absorption spectroscopy (PM-IRRAS) were also consistent with the results of a surface pressure–area isotherm. Here, a reaction mechanism explaining these observations is presented and discussed. The results of PM2.5 and SOA samples will contribute to our understanding of the processing of organic aerosol aging that alters the aerosol composition.

Tribological Properties of Composite Langmuir–Blodgett Coatings of OLEIC Acid with Molybdenum Disulfide Nanoparticles

Tribological properties of composite Langmuir–Blodgett monolayers of oleic acid (OA) with MoS2 nanoparticles formed on silicon surfaces by the horizontal precipitation method were studied. Incorporation of MoS2 (the average particle size [Formula: see text][Formula: see text]nm) into the structure of the layer was found to result in the increase of minimal area per molecule from 0.43[Formula: see text]nm2 to 0.58[Formula: see text]nm2 and wear stability of OA monolayer.

Temperature, pH, and Molecular Packing Effects on the Penetration of Oleic Acid Monolayer by α-Lactalbumin.

Recently, we reported on the interfacial behavior of mixed oleic acid (OA)-α-lactalbumin monolayer and its relevance in the formation of tumoricidal HAMLET (human α-lactalbumin made lethal to tumor cells)-like complex. This complex is probably formed in the gastrointestinal tract, but it has not been proved so far. The molecular base and the underlying physicochemical forces leading to such complexation remain to be known as well. There are also several other issues related with the complex stoichiometry that need to be fully explained. This study provides insight into the mechanism of temperature, pH, and physical state of monolayer-dependent binding of OA by the milk protein- apo-α-lactalbumin. Using the Langmuir and Langmuir-Blodgett approaches, we investigated the interactions between the OA monolayer and the apo-bovine α-lactalbumin (BLA III) at different pH, temperatures, and molecular packing. We found that the most favorable conditions for the formation of mixed OA-BLA III film are relevant to the gastric environment. The stabilization of OA-BLA III at the interface is associated with the conformational changes of protein in the presence of fatty acids induced by low pH and high temperature in the expanded monolayer. Our approach helps to understand the molecular mechanism of HAMLET/bovine α-lactalbumin made lethal to tumor cells formation in vivo.

Establishing a model organic film of low volatile compound mixture on aqueous aerosol surface

Long chain fatty acids and alcohols are low volatile species in continental and marine aerosols. We established a surface film model by Langmuir trough to investigate the interfacial properties of sea salts droplets coated by surface active molecules—stearic acid (SA), oleic acid (OA), 1-octadecanol (C18OH) and their mixtures. The aim of this work was to verify the impact of the head group, saturation degree, mixing ratio of different surfactants on miscibility and stability between these compounds in monolayers at the air–water interface. Compared to the organic-coated water droplets, the surface properties of mixed fatty acid and alcohol-coated aqueous sea salt particles are substantially different. Mixed SA/C18OH monolayers are less stable than pure SA or C18OH monolayer at high surface pressure. From the point of view of the geometry, steric hindrance of unsaturated chain is the crucial factor in loose packing of OA monolayer. The negative values of excess mixing areas (ΔAex) for OA/C18OH monolayer on artificial seawater result from the attractive interaction between tail groups. The maximum negative value of excess Gibbs free energies (ΔGex) appears at the equimolecular OA and C18OH. Surface pressure−area (π–A) isotherm combined with equilibrium spreading pressure (ESP) confirms that the tightly packed monolayer formed by C18OH molecules can minimize water evaporation rate of the potential droplet. Different surface properties of organic films coated on aqueous aerosol must have a significant impact on interaction droplet growth. The interactions between fatty acid and alcohol at the air-water interface provide an insight into the nucleation and growth mechanism of droplets covered by film-forming species.

Binding of α-lactalbumin to oleic acid monolayer and its relevance to formation of HAMLET-like complexes

The α-lactalbumin from human milk forms a cytotoxic protein-fatty acid complex with oleic acid (OA) called HAMLET, which is probably formed in the stomach of a breastfed infant. However, the mechanism of this process is still unclear and in vivo synthesis of this tumoricidal complex has not yet been observed. We used a Langmuir monolayer approach to form an OA monolayer and study the interactions between this fatty acid and milk proteins. The results revealed irreversible adsorption of α-lactalbumin from bovine milk and human milk α-lactalbumin followed by the penetration of the OA monolayer. The process was found to be governed mainly by hydrophobic interactions between protein and the fatty acid. Binding of OA and α-lactalbumin led to the formation of a stable interfacial film that was recognisable as a HAMLET-like complex. These results give credence to the concept of HAMLET formation in a newborn's gastrointestinal system.

Understanding the Molecule-Electrode Interface for Molecular Spintronic Devices: A Computational and Experimental Study.

A triple-decker SYML-Dy2 single-molecule magnet (SMM) was synthetized and grafted onto the surface of iron oxide nanoparticles (IO-NPs) coated by an oleic acid monolayer. The magnetism of the SYML-Dy2 complex, and the hybrid system, NP-Dy2, were studied by a superconducting quantum interference device (SQUID). Density functional theory (DFT) calculations were carried out to study both the energetics of the interaction between SYML-Dy2 complex to the organic capping, and the assembly presented by the oleic acid chains.

Thermodynamic Behaviour of Mixed Films of an Unsaturated and a Saturated Polar Lipid. (Oleic Acid-Stearic Acid and POPC-DPPC)

Mixed fatty acids or mixed phospholipids systems with saturated-unsaturated hydrocarbon chains are of biological interest. In this work, the monolayers of oleic acid-stearic acid (OA-SA) and palmitoyloleoylphosphatidylcholine-dipalmitoylphosphatidylcholine (POPC-DPPC) have been studied. From the surface pressure-area isotherms, elastic modulus values and virial equation coefficients can be obtained. Thermodynamic treatment also yields excess (GE) and mixing (ΔGmix) free energies. Results indicate positive GE values, that is, molecular interactions in the mixed films are less favourable, due to the presence of unsaturation; however, the mixture is slightly favourable due to the entropic factor that affords positive ΔGmix values. For the OA-SA system, a high SA content and surface pressure facilitate the phase separation, even though a certain miscibility between both components still remains. For the POPC-DPPC system, the most favourable mixing conditions occur for XPOPC ≈ 0.4. For these mixed systems, the values of the elastic modulus are more similar to those of more fluid components (OA or POPC); analysis of the virial coefficients shows that the b1 virial coefficient values lie between those of the individual components and are higher than values suitable for an ideal mixing.

Oleic Acid Surface Modification in the Preparation of Magnetic Nanoparticles by a Chemically Induced Transition

Using a chemically induced transition method, magnetic nanoparticles of $\gamma $ -Fe2O3 coated by FeCl3 $\cdot $ 6H2O ( $\gamma $ -Fe2O3/FeCl3 $\cdot$ 6H2O nanoparticles) can be prepared. Surface modification is performed using oleic acid. By adding oleic acid during the synthesis, FeCl3 $\cdot$ 6H2O can be replaced to produce nanoparticles of $\gamma $ -Fe2O3 coated by a monolayer of oleic acid ( $\gamma $ -Fe2O3/oleic acid nanoparticles). The amount of oleic acid added is sufficient, with the as-prepared sample single $\gamma $ -Fe2O3/oleic acid nanoparticles, whereas the as-prepared sample is a mixture of both $\gamma $ -Fe2O3/FeCl3 $\cdot$ 6H2O and $\gamma $ -Fe2O3/oleic acid nanoparticles. By chemical species analysis, the mass fraction of both the $\gamma $ -Fe2O3 phase and oleic acid adsorbed can be estimated. These magnetic nanoparticles coated by oleic acid can be considered as effective nanoparticles with an effective density $\rho _{\mathrm {p.e}}$ . The $\rho _{\mathrm {p.e}}$ reflects the amount of oleic acid chemisorbed on the nanoparticles. A kerosene-based suspension comprising the effective nanoparticles was synthesized. Results for the specific saturation magnetization $\sigma _{\mathrm {f.s}}$ and density $\rho _{\mathrm {f}}$ of the suspension confirm the effective particle structure, involving the mass fraction of oleic acid adsorbed and the effective density of the effective particles.

Emerging investigator series: exploring the surface properties of aqueous aerosols coated with mixed surfactants.

Mixed Langmuir monolayers of cholesterol with both saturated and unsaturated fatty acids, stearic acid (SA), and oleic acid (OA) spread at the air-seawater surface were studied. The phase behavior, molecular interaction, and conformational order of the monolayers were investigated by surface pressure-area (π-A) isotherms and infrared reflection-absorption spectroscopy (IRRAS) measurements. The thermodynamic parameters of the mixed films, including excess molecular area and excess Gibbs free energy were calculated by using the isotherm data. The interaction between SA (or OA) and cholesterol varied with the molar fraction of the fatty acids and surface pressure. OA/chol monolayers showed the characteristics of miscibility, but they acted as nonideal systems. Cholesterol has been observed to have a stabilizing effect on OA monolayers. The negative values of the excess Gibbs free energy in the entire composition range demonstrated that mixed OA/chol monolayers were thermodynamically stable. IRRAS spectra showed that mixing with cholesterol changes the ordering of fatty acid monolayers at the air-seawater surface. The findings provide general information regarding the structural changes in the monolayer induced by lateral packing. These results help in the understanding of the mixing behavior of fatty acids and cholesterol and provide insights into the fate of the mixed-monolayer-coated sea salt aerosol in the ocean environment.

Ferrofluid-based magnetorheological fluids: tuning the properties by varying the composition at two hierarchical levels

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 induction B in the MR cell. A wide range of the magnetic particle volume fractions were considered at the two hierarchical levels involved: at the nanometer level, φ = 2.75, 11.67, and 22.90 %, and at the micrometer level, Φ Fe = 5–40 %. Taking into account also the oleic acid monolayer coating of the magnetite nanoparticles, the hydrodynamic volume fraction of the most concentrated ferrofluid results to be 65 % and, consequently, the highest value of the effective total volume fraction of the investigated extremely bidisperse MR fluids attains 85 %. The diagrams of the static and dynamic (Bingham) yield stresses and of the magnetoviscous effect offer an adequate choice of the nanometer and micrometer range particle volume fractions to fulfill the specific requirements of high-pressure rotating seals and of various MR devices.

Magnetically Controlled Release of Dispersed Iron Oxide Nanoparticles from Imprinted Organic Thin Films

Iron oxide nanoparticles (Fe3O4-NP) were compressed together with oleic acid (OA) in a Langmuir-Blodgett trough. Optimized dilution of the NP allowed the transfer of two-dimensional nanocomposites of Fe3O4-NP and OA to gold substrates. The characterization of the two-dimensional composite by scanning force microscopy (SFM) showed the existence of a sub-monolayer coverage with a few NP being pushed into the second layer. Polarization modulation infrared reflection absorption spectra (PM IRRAS) showed the presence of oleic acid. The nanoparticles could be removed in an external magnetic field of a permanent magnet as evidenced by SFM while the OA monolayer was left on the gold substrate as shown by PM IRRAS. Such composite layers can be used for the controlled release of specified small amount of intact NP.

Yield stress and flow behavior of concentrated ferrofluid-based magnetorheological fluids: the influence of composition

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 varying from Φ Fe = 5 to 40 %. The ferrofluid carrier has φ p = 23 % solid volume fraction of magnetic nanoparticles stabilized with chemisorbed oleic acid monolayer and without any excess surfactant. In the absence of the field, the ferrofluid has a quasi-Newtonian behavior with a weak shear thinning tendency. The static yield stress shows an increase of about 3 orders of magnitude for an iron particle content of approx. Φ Fe = 25 % (Φ tot = 42.25 %), while above this value, a saturation tendency is observed. The dynamic yield stress (Bingham model) also increases with the magnetic induction and the particle volume fraction; however, the saturation of the MR effect is less pronounced. The relative viscosity change has a maximum at Φ Fe = (10–15) % due to the accelerated increase of the effective viscosity of the composite for higher Fe content. Addition of micrometer-sized iron particles to a concentrated ferrofluid without any supplementary stabilizing agent proved to be a direct and simple way to control the magnetorheological and magnetoviscous behavior, as well as the saturation magnetization of the resulting nano-micro composite fluid to fulfill the requirements of their use in various MR control and rotating seal devices.