Oleic Acid Monolayer Research Articles

Super-low friction of ta-C coating in presence of oleic acid

Abstract Friction tests have been carried out on bearing steel friction pairs coated with a-C:H and ta-C under lubricated conditions with 1-hexadecene and pure oleic acid, respectively. Main results show that ta-C leads to the super-low regime with oleic acid (friction coefficient below 0.01) and that a-C:H is quite well lubricated by 1-hexadecen. Surface analyses by coupling X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) have been carried out in the case of oleic acid with ta-C and a-C:H coatings. Results show that tribochemical reactions have occurred. OH groups terminate the ta-C surface whereas a-C:H is covered by a thin tribofilm and is terminated by oleic acid monolayers. The superlow regime in the case of ta-C is mainly attributed to the presence of the OH-termination.

Quantitative Time-Resolved Vibrational Sum Frequency Generation Spectroscopy as a Tool for Thin Film Kinetic Studies: New Insights into Oleic Acid Monolayer Oxidation

Environmental air-water interfaces are often covered by thin films of surface-active organic substances that play an important role for air-sea gas exchange and aerosol aging. Surface-sensitive vibrational sum frequency generation (VSFG) spectroscopy has been widely used to study the static structure of organic monolayers serving as simple model systems of such films. Probably due to the difficulties to correlate the SFG signal intensity with the surface concentration, corresponding time-resolved studies of surface reactions are scarce. In this study, quantitative time-resolved measurements have been performed on the oleic acid monolayer ozonolysis, which is considered a benchmark system for investigating the reactivity and fate of unsaturated natural organics. Surface concentration calibration data have been obtained by combining the pressure-area isotherm and VSFG spectra acquisition such that the 2D phase behavior of the oleic acid film could be properly taken into account. In contrast to literature reports, surface-active oxidation products were found to be negligible and do not interfere with the VSFG measurements. A pseudo-first-order kinetic analysis of the time-resolved data yielded a bimolecular rate constant of k2(oleic acid + O3 → products) = (1.65 ± 0.64) × 10(-16) cm(3) molecules(-1) s(-1), corresponding to an uptake coefficient of γ = (4.7 ± 1.8) × 10(-6). This result is in very good agreement with most recent monolayer measurements based on alternative methods and underlines the reliability of the time-resolved VSFG approach.

Effect of perfluoroalkyl chain length on monolayer behavior of partially fluorinated oleic acid molecules at the air–water interface

A series of oleic acid (OA) analogs containing terminal perfluoroalkyl groups (CF3, C2F5, n-C3F7, n-C4F9 or n-C8F17) was synthesized to clarify how the fluorinated chain length affects the stability and molecular packing of liquid-expanded OA monolayers at the air–water interface. Although the substitution of terminal CF3 group for CH3 in OA had no effect on monolayer stability, further fluorination led to a gradual increase in monolayer stability at 25̊C. Surface pressure–area isotherm revealed that partially fluorinated OA analogs form more expanded monolayers than OA at low surface pressures, and that the monolayer behavior of OA analogs with the even-carbon numbered fluorinated chain is almost the same as that of OA upon monolayer compression, whereas the behavior of OA analogs with the odd-carbon numbered fluorinated chain significantly differs from that of OA. These results indicate: (i) the terminal short part (at least C2 residue) in OA predominantly determines the liquid-expanded monolayer stability; (ii) the molecular packing state of OA may be perturbed by the substitution of a short odd-carbon numbered fluorinated chain; (iii) hence, OA analogs with even-carbon numbered chain are considered to be preferable as hydrophobic building blocks for the synthesis of fluorinated phospholipids.

Large scale solvothermal synthesis and a strategy to obtain stable Langmuir–Blodgett film of CoFe2O4 nanoparticles

Nearly monodisperse oleic acid coated cobalt ferrite nanoparticles were synthesized in large scale by a simple solvothermal method utilizing N-methyl 2-Pyrrolidone (NMP) as a high boiling solvent. The magnetic oxide was further investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). Langmuir–Blodgett (LB) technique is discussed to obtain a 2D assembly of oleic acid coated CoFe2O4 nanoparticles over a large area. We describe a method to obtain stable, condensed three layers of cadmium arachidate on a piranha treated glass substrate. The hydrophobic surface thus obtained was subsequently used for forming a stable monolayer of oleic acid stabilized cobalt ferrite nanoparticles at the air–water interface. The stability of the LB films at the air–water interface was studied by pressure–area isotherm curves and atomic force microscopy (AFM) cross sectional height profile analysis. 2D organization of the magnetic nanoparticles at different surface pressures was studied by TEM. Preparation of large area LB films of CoFe2O4 nanoparticles is reported for a surface pressure more than 15mN/m.

Polysaccharide-anchored fatty acid liposome

In this study, the preparation of N-pamitoyl chitosan (ChP) anchored oleic acid (OA) liposome was demonstrated. Two different types of water-soluble ChPs with different degrees of acylation (DA) were selected for this study. The presence of ChPs on the surface of OA liposome was confirmed with their micrographs and physicochemical properties. The "peeling off" effect on the surface of the ChP-anchored OA (OAChP) liposomes was observed on the atomic force microscope micrographs and confirmed the presence of the ChPs layer on the liposome surface. The surface tension of the OAChPs liposome solution was found to be higher than that of the OA liposome solution. This result indicated the removal of OA monomer by ChPs from the air-water interface. The increase in the minimum area per headgroup (A(min)) of the OA with the presence of ChPs has further proved the interaction between OA monomer and the hydrophobic moieties of the ChPs. The ChPs anchored onto the OA monolayer increased the curvature of the OAChP liposomes monolayer and reduced the liposome size. The size of the OAChP liposomes was reduced by 30 nm as compared with the unmodified OA liposome. Results revealed that the anchored ChPs can improve the integrity and rigidity of the OA liposome.

Low Friction Property of Diamond-Like Carbon Coating Films and Oxygen Transmission Ratio of Amorphous Carbon Films Deposited by Advanced Coating Processes

The topics of the applied technology of amorphous carbon film to reduce friction using diamond-like carbon (DLC) coated by the vacuum arc ion plating process and to improve the gas barrier property using the amorphous carbon film by the atmospheric pressure plasma process are introduced with the basic experimental results. For reducing friction, the super low friction coefficient below 0.01 has been found when the tetrahedral amorphous carbon coating deposited by T-shape filtered arc deposition method [ta-C(T)] was evaluated the friction property under oleic acid lubrication at pure sliding condition. It was thought that the low share strength tribofilm composed of water and oleic acid mono-layer seemed to be formed on the sliding interface. For gas barrier performance, the amorphous carbon film deposited by the atmospheric pressure plasma chemical vapour deposition (CVD) technique on poly(ethylene terephthalate) (PET) substrate was improved the oxygen transmission ratio (OTR) around 30% compared with that of uncoated PET substrate. These advanced performance obtained by the optimum material combination of DLC with lubricant and the original atmospheric pressure plasma CVD technique are expected to be applied on the actual application for the different types of the industrial fields in near future.

Study on the properties and stability of ionic liquid-based ferrofluids

Ionic liquid (IL)-based ferrofluids have been prepared dispersing both bare and sterically stabilized CoFe2O4 nanoparticles. The precipitated particles were characterized by X-ray diffraction, scanning electronic microscopy, transmission electron microscopy, Fourier transform infrared, and vibrating sample magnetometry studies. The water-absorbing property of ferrofluids at ambient temperature was estimated by weight and viscosity measurements. Colloidal dispersion stability of the ferrofluids was evaluated by particle suspension percentage. Experimental results indicate that interparticle electrostatic repulsion is not effective in stabilizing bare magnetic particles in IL. There is no significant increase on the dispersion stability when the particles were coated with a monolayer of oleic acid. The reason could be caused by the incompatibility between the nonpolar tail of surfactant and carrier liquid. When excess oleic acid was added into IL, stable magnetic colloid was achieved by a steric stabilization layer coated to be compatible with the IL.

Magnetic Nanoparticles and Rapamycin Encapsulated into Polymeric Nanocarriers

The objective of this study was to develop nanocapsules and nanospheres of polylactide-co-glycolide (PLGA) containing magnetic nanoparticles and rapamycin. Magnetic nanoparticles (MP) were obtained by the co-precipitation of Fe(ll) and Fe(III) salts by addition of ammonium hydroxide. Nanocapsules (NC) and nanospheres (NS) containing either uncoated magnetic nanoparticles (MP), MP coated with oleic acid monolayer (MPOA) or MP coated with oleic acid bilayer (MPOA-OA) were prepared by the emulsion evaporation method. Rapamycin was also encapsulated into NC and NS. Morphology, size, size distribution, entrapment efficiency, stability and magnetization characteristics were determined. Non-contact AFM images showed that the composite nanoparticles were almost spherical in shape. The resulting polymeric nanocarriers were found to have a mean diameter of approximately 120 nm with a narrow size distribution. The influence of some experimental parameters on the entrapment efficiency and stability was determined. Nanocapsules and nanospheres prepared with uncoated magnetic nanoparticles exhibited higher entrapment efficiency and stability. Superparamagnetic behavior of the magnetic nanocomposite was demonstrated by magnetization data. These findings may contribute to the development of potential controlled release drug targeting devices based on magnetic polymeric nanocarriers.

In vitro biocompatibility assessment of functionalized magnetite nanoparticles: Biological and cytotoxicological effects

In the biomedical field, nanomaterials have the potential for use in the targeted delivery of drugs in the human body and in the diagnosis and therapy of certain diseases. In the category of targeted delivery, magnetite (Fe(3)O(4)) nanoparticles have received much attention. As with any similar new therapy, when such nanoparticles are functionalized with chemical groups designed to permit the specific attachment of drugs, cytotoxicological testing is necessary before moving to animal models. Here, we consider several variously functionalized magnetite nanoparticles, including those prepared with (1) a monolayer of oleic acid (Fe(3)O(4)@OA), which is subsequently converted to (2) a shell of amine-containing silane (Fe(3)O(4)@NH(2)), (3) a shell of silica (Fe(3)O(4)@SiO(2)), and (4) a shell of amine-containing silane over a shell of silica (Fe(3)O(4)@SiO(2)@NH(2)). These latter three functionalities were evaluated for biocompatibility, cellular morphology, mitochondrial function (MTT assay), lactate dehydrogenase membrane leakage (LDH assay), and proinflammatory potential through enzyme linked immunosorbent assay (ELISA) for interleukin 6 (IL-6). Controlled tests were performed over a period of 72 h, with results showing LDH leakage and abnormal Il-6 secretion at high concentrations (>50 μg/mL). The tests showed that, in addition to the surface characteristics of the nanoparticles, both the nutrient medium and the time of suspension before exposure to cells also contribute to nanoparticle cytotoxicity.

Determination of molecular groups involved in the interaction of annexin A5 with lipid membrane models at the air–water interface

Annexin A5 (AnxA5) is a member of a family of homologous proteins sharing the ability to bind to negatively charged phospholipid membranes in a Ca(2+)-dependent manner. In this paper, we used polarization-modulated infrared reflection absorption spectroscopy (PMIRRAS), Brewster angle microscopy (BAM), and ellipsometry to investigate changes both in the structure of AnxA5 and phospholipid head groups associated with membrane binding. We found that the secondary structure of AnxA5 in the AnxA5/Ca(2+)/lipid ternary complex is conserved, mainly in alpha-helices and the average orientation of the alpha-helices of the protein is slightly tilted with respect to the normal to the phospholipid monolayer. Upon interaction between AnxA5 and phospholipids, a shift of the nu(as) PO(2)(-) band is observed by PMIRRAS. This reveals that the phosphate group is the main group involved in the binding of AnxA5 to phospholipids via Ca(2+) ions, even when some carboxylate groups are accessible (PS). PMIRRAS spectra also indicate a change of carboxylate orientation in the aspartate and glutamate residues implicated in the association of the AnxA5, which could be linked to the 2D crystallization of protein under the phospholipid monolayer. Finally, we demonstrated that the interaction of AnxA5 with pure carboxylate groups of an oleic acid monolayer is possible, but the orientation of the protein under the lipid is completely different.

Interaction of nitrogen dioxide (NO 2) with a monolayer of oleic acid at the air–water interface – A simple proxy for atmospheric aerosol

The reactions between atmospheric oxidants and organic amphiphiles at the air–water interface of an aerosol droplet may affect the size and critical supersaturation required for cloud droplet formation. We demonstrate that no reaction occurs between gaseous nitrogen dioxide (1000 ppm in air) and a monolayer of an insoluble amphiphile, oleic acid ( cis-9-octadecenoic acid), at the air–water interface which removes material from the air–water interface. We present evidence that the NO 2 isomerises the cis-9-octadecenoic (oleic) acid to trans-9-octadecenoic (elaidic) acid. The study presented here is important for future and previous studies of (1) the reaction between the nitrate radical, NO 3, and thin organic films as NO 2 is usually present in high concentrations in these experimental systems and (2) the effect of NO 2 air pollution on the unsaturated fatty acids and lipids found at the air–liquid surface of human lung lining fluid.

Structuralization of Magnetic Nanoparticles Induced by Laser Heating in Magnetic Fluids

The structuralization of magnetic particles in magnetic fluids due to the thermodiffusion induced by laser light illumination was experimentally observed in two types of magnetic fluids: one based on a mineral oil with magnetite particles covered by a monolayer of oleic acid as a surfactant and the other a kerosene-based magnetic fluid sterically stabilized by a double layer consisting of oleic acid and dodecylbenzenesulphonic acid (DBS). Forced Rayleigh scattering (FRS) showed different behaviors of magnetic particle structuralization in the observed magnetic fluids. While for the case of mineral oil-based magnetic fluids, there was observed a positive thermodiffusion (S > 0), an indication of negative thermodiffusion (S < 0) was observed in magnetic fluids based on kerosene. This was also confirmed by the time-dependent decay of a grating of magnetic particles. Numerical simulation of aggregation for the case of negative thermodiffusion was confirmed by the observed aggregation after laser illumination in kerosene-based magnetic fluids and enabled an estimated value of the negative Soret constant in the magnetic fluid studied (S ≈ −10−2 K−1).

Oxidation of oleic acid at the air–water interface and its potential effects on cloud critical supersaturations

The oxidation of organic films on cloud condensation nuclei has the potential to affect climate and precipitation events. In this work we present a study of the oxidation of a monolayer of deuterated oleic acid (cis-9-octadecenoic acid) at the air-water interface by ozone to determine if oxidation removes the organic film or replaces it with a product film. A range of different aqueous sub-phases were studied. The surface excess of deuterated material was followed by neutron reflection whilst the surface pressure was followed using a Wilhelmy plate. The neutron reflection data reveal that approximately half the organic material remains at the air-water interface following the oxidation of oleic acid by ozone, thus cleavage of the double bond by ozone creates one surface active species and one species that partitions to the bulk (or gas) phase. The most probable products, produced with a yield of approximately (87 +/- 14)%, are nonanoic acid, which remains at the interface, and azelaic acid (nonanedioic acid), which dissolves into the bulk solution. We also report a surface bimolecular rate constant for the reaction between ozone and oleic acid of (7.3 +/- 0.9) x 10(-11) cm2 molecule s(-1). The rate constant and product yield are not affected by the solution sub-phase. An uptake coefficient of ozone on the oleic acid monolayer of approximately 4 x 10(-6) is estimated from our results. A simple Kohler analysis demonstrates that the oxidation of oleic acid by ozone on an atmospheric aerosol will lower the critical supersaturation needed for cloud droplet formation. We calculate an atmospheric chemical lifetime of oleic acid of 1.3 hours, significantly longer than laboratory studies on pure oleic acid particles suggest, but more consistent with field studies reporting oleic acid present in aged atmospheric aerosol.

Oxidation of oleic acid at air/liquid interfaces

Oxidation of oleic acid monolayers by ozone was studied to understand the fate of fat‐coated aerosols from both freshwater and saltwater sources. Oleic acid monolayers at the air/water interface and at the air/sodium chloride solution interface were investigated using surface‐specific, broad‐bandwidth, sum frequency generation spectroscopy. Complementary techniques of infrared reflection adsorption spectroscopy and surface pressure measurements taken during monolayer oxidation confirmed the sum frequency results. Using this nonlinear optical technique coupled with a Langmuir trough, concurrent spectroscopic and thermodynamic data were collected to obtain a molecular picture of the monolayers. No substantial difference was observed between oxidation of monolayers spread on water and on 0.6 M sodium chloride solutions. Results indicate that depending on the size of the aerosol and the extent of oxidation, the subsequent oxidation products may not remain at the surface of these films, but instead be dissolved in the aqueous subphase of the aerosol particle. Results also indicate that oxidation of oleic acid could produce monolayers containing species that have no oxidized acyl chains.

Kinetic analysis of the ozone processing of an unsaturated organic monolayer as a model of an aerosol surface

It has been suggested that an organic aerosol containing unsaturated organic compounds at the surface would likely be processed by atmospheric ozone. The ozonolysis of oleic acid gives rise to the formation of products having shorter chain lengths than the starting molecule, and are consequently more water soluble than oleic acid. Hence, the exposure of a monolayer of oleic acid to ozone should lead to a decrease in surface activity at the air-water interface. A model system is used for real-time measurements of surface tension changes due to ozone exposure of a pendant drop that is coated by a fatty acid monolayer. The surface tension is measured based on an analysis of the shape profile of acquired images of the drop. A study of the kinetics of the gas-surface reaction is presented. Assuming that the uptake of ozone is dominated by the reaction at the surface, the measured reactive uptake coefficient of ozone gamma(meas) is estimated to be (2.6 +/- 0.1) x 10(-6).

Competition between Atmospherically Relevant Fatty Acid Monolayers at the Air/Water Interface

Competition and oxidation of fatty acids spread at the air/water interface were investigated using surface-specific, broad-bandwidth, sum frequency generation spectroscopy. At the air/water interface, a monolayer of oleic acid replaced a monolayer of deuterated palmitic acid at equilibrium spreading pressure. Subsequent oxidation of the oleic acid monolayer with ozone resulted in products more water soluble than the palmitic acid; therefore, the palmitic acid monolayer reformed at the surface. Results indicate that the surfactants on the surface of fat-coated tropospheric aerosols will only possess oxidized acyl chains after all less soluble species in the aqueous subphase have been removed through the processes of replacement at the surface and atmospheric oxidation.

Silica encapsulation and magnetic properties of FePt nanoparticles

Core–shell nanoparticles have emerged as an important class of functional nanostructures with potential applications in many diverse fields, especially in health sciences. We have used a modified aqueous sol–gel route for the synthesis of size-selective FePt@SiO 2 core–shell nanoparticles. In this approach, oleic acid and olyel amine stabilized FePt nanoparticles are first encapsulated through an aminopropoxysilane (APS) monolayer and then subsequent condensation of triethoxysilane (TEOS) on FePt particle surface. These well-defined FePt@SiO 2 core–shell nanoparticles with narrow size distribution become colloidal in aqueous media, and can thus be used as carrier fluid for biomolecular complexes. In comparison, the scarce hydrophilic nature of oleic acid monolayers on FePt particle surface yields an edgy partial coating of silica when only TEOS is applied for the surface modification. The synthesized core–shell nanoparticles were characterized by direct techniques of high resolution transmission electron microscopy (HRTEM), EDS and indirectly via UV–vis absorption and FTIR studies. The FePt@SiO 2 nanoparticles exhibit essential characteristics of superparamagnetic behavior, as investigated by SQUID magnetometry. The blocking temperatures ( T B) of FePt and FePt@SiO 2 (135 and 80 K) were studied using zero field cooled (ZFC)/field cooled (FC) curves.

A kinetic study of the formation of β-cyclodextrin complexes with monomolecular films of fatty acids and glycerides spread at the air/water interface

The kinetics of formation of inclusion complexes between β-cyclodextrin and monolayers of one-, two- and three-chained lipid molecules, namely, oleic acid (OA), monoolein (MO), diolein (DO) and triolein (TO), was investigated at various pH using three independent dynamic methods. The formation and solubilization of soluble inclusion β-CD/OA and β-CD/MO complexes was detected by measuring the decrease of the surface area and surface pressure of the OA and MO monolayers in the presence of β-CD within a wide range of concentrations. A third approach, describing the dilatational properties of the monolayers, influenced by the formation and solubilization of the complexes, was developed. Using the three above-mentioned independent methods, the rate constants of formation ( k 1) and dissociation ( k 2) of β-CD/OA and β-CD/MO, were determined. We observed that solubilization flux i s for OA monolayer increases with pH and at pH 11 reached a value, which is closed to the diffusion flux i D and the process thus becomes diffusion controlled. For MO monolayer no significant effects of pH was observed above pH 6. The surface pressure (Δ π) – area per molecule ( A) and surface potential (Δ V) – area per molecule ( A) isotherms and rheological properties of DO and TO monolayers were measured in the presence or absence of β-CD. DO and TO form water-insoluble complexes with β-CD, as visualized by AFM images.

Structure and denaturation of adsorbed lysozyme at the air–water interface

Adsorption of lysozyme at the surface of a buffer solution at 25 °C, pH 7, and ionic strength 0.1 is studied under different denaturing conditions using on X-ray reflectometry technique. When the lysozyme is fully denatured with urea and dithiothreitol (DTT), its measured adsorption profile is very well explained by the scale law ( z −4/3) profile theoretically predicted for polymer adsorption. When no denaturing agent is present, a monolayer is also produced, but the adsorption profile cannot be explained by a monolayer of nondenatured lysozyme; furthermore, it is close to the one obtained for lysozyme partially denatured with urea. A PMIRRAS study of native lysozyme adsorbed at the air–buffer interface shows that the secondary structure of the protein is modified: most of the α-helices are replaced by β-sheets. In contrast, when the lysozyme is adsorbed below a monolayer of oleic acid at the air–buffer interface, that is, on a hydrophilic interface, the protein forms a monolayer whose thickness, 3.0 nm, is equal to one dimension of crystallized lysozyme. Under such conditions, the adsorbed protein is not denatured. Thus the hydrophobic nature of the air–water interface yields partial denaturation of the protein upon adsorption, but the disulfur bridges and β-sheets prevent total denaturation.

Effects of Water-Soluble Alcohols on the Surface Conductance of Lipid Monolayers: Bimodal Action

We (Yoshida et al. J. Phys. Chem. B 2000, 104, 1249) devised a submersible horizontal electrode for estimation of the conductance of surface monolayers. The effects of 1-propanol on the electrical conductance of surface monolayers of stearic, elaidic, and oleic acids were estimated. The effects depend on the structures of the hydrophobic part of the monolayers. The surface electrical conductance of a stearic acid monolayer increased 18-fold by the addition of 1-propanol. However, the response of an oleic acid monolayer was almost negligible. The result suggests that alcohol effects on the surface electrical conductance depend strongly on the packing of the monolayers, therefore it is affected by changes in the alkyl tails. Because alcohol molecules in water anchor to the monolayer surface, sandwiched water molecules between the alcohol and monolayer form two-dimensional structures. The solid condensed form of the stearic acid membrane tends to form two-dimensional structures of sandwiched water. The magnitude of their structures depends on the condensability of the monolayer. We contend that the proton flow through the hydrogen-bond network of water (electrical conductance) increases.