Oleic Acid Surfactant Research Articles

Anisotropic CeCo5 based permanent magnetic nanoflakes with high coercivity

ABSTRACTMagnetic anisotropic CeCo5 nanoflakes with nominated compositions of CeCo4.5Cu0.5Fe0.5 were prepared by surfactant assistant high-energy ball milling (SA-HEBM) with oleic acid as the surfactant and heptanes as the solvent. The crystal structure, morphology, and magnetic properties of these CeCo5 nanoflakes, were examined with scanning electronic microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM), respectively. The infrared absorption spectroscopy (FT-IR) was used to study the evolution of surface structure of oleic acid coated CeCo5 nanoflakes. Results show that CeCo5 nanoflakes have an average thickness of tens of nanometers, an average particle size of ∼3 μm, a relatively large aspect ratio, high room temperature (RT) coercivity of 5.4 kOe, and significant geometrical and magnetic anisotropy. The oleic acid surfactant in the SA-HEBM process plays an important role in the formation and development process of the obvious magnetic anisotropy of CeCo5 nanoflakes.

Study of the structural features of ε-Co nanoparticles synthesized by cobalt carbonyl decomposition in the presence of surfactant

Cobalt nanoparticles (3–7 nm in size) obtained by cobalt carbonyl decomposition in 1,2-dichlorobenzene in the presence of surfactants (trioctylphosphine oxide and oleic acid) have been studied by a complex of structural methods: small-angle X-ray scattering, electron diffraction, and transmission electron microscopy. The nanoparticles synthesized are found to consist of the cubic e-Со phase; their crystal structure is described within the sp. gr. P4132, a = 6.097 A. Using small-angle X-ray scattering, the size and shape of nanoparticles have been determined directly in the liquid dispersion. Most of the particles have a spherical shape; their average size is ≈3.5 ± 0.5 nm, which agrees with the electron microscopy data. Possible factors causing the e-phase formation during synthesis of metallic Co nanoparticles are discussed.

Lead-Free, Air-Stable All-Inorganic Cesium Bismuth Halide Perovskite Nanocrystals.

Lead-based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead-based and the other is the poor stability. Lead-free all-inorganic perovskite Cs3 Bi2 X9 (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand-free Cs3 Bi2 Br9 NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2-20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.

Lead‐Free, Air‐Stable All‐Inorganic Cesium Bismuth Halide Perovskite Nanocrystals

AbstractLead‐based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead‐based and the other is the poor stability. Lead‐free all‐inorganic perovskite Cs3Bi2X9 (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand‐free Cs3Bi2Br9 NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2–20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.

Highly dispersible and uniform size Cu2ZnSnS4 nanoparticles for photocatalytic application

Highly dispersible, uniform size (∼7nm) single-phase Cu2ZnSnS4 nanoparticles have been synthesized by hydrothermal method using non-toxic surfactant (oleic acid). High resolution transmission electron microscopy image indicates good crystallinity of the Cu2ZnSnS4 nanoparticles with the growth along (112) plane. X-ray photoelectron spectroscopy analyses suggested that the formation of with Cu, Zn, and Sn in +1, +2 and +4 oxidation states. The optical absorption spectrum of Cu2ZnSnS4 nanoparticles exhibits an absorption in the visible region and its optical band gap was found to be ∼1.72eV, which could be much more appropriate for photocatalytic application under visible light irradiation. These Cu2ZnSnS4 nanoparticles have been shown high photocatalytic degradation activity of methylene blue (MB) dye in the presence of visible light irradiation. The rate constant (k) value of Cu2ZnSnS4 nanoparticles is found to be 0.0144min−1. We have discussed the mechanism of dye degradation process that drives the photocatalytic degradation process. The reusability of the Cu2ZnSnS4 nanoparticles for the dye degradation is also demonstrated.

Temperature Dependence and Impedance Characteristics of Hybrid Solar Cells Based on Poly(phenylene vinylene): ZnO Nanoparticles With Added Surfactants

A recent study has shown that the use of a semiconducting surfactant in hybrid bulk heterojunction solar cells based on poly[2-methoxy-5-(3',7'-dimethyloctyloxyl)-1,4-phenylene vinylene] and zinc oxide significantly increases their performance. To further study the mechanism underlying the improved performance resulting from the addition of a semiconducting surfactant, we compared the temperature and light intensity dependence of the current voltage characteristics and impedance spectra of devices that used no surfactant, an insulating oleic acid (OA) surfactant, or a semiconducting 2-(2-ethylhexyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic acid (BQ) surfactant. The temperature and light intensity dependence data enabled us to extract the activation energy for different devices, and we measured the junction resistance through impedance spectroscopy. The device that used BQ had significantly lower activation energy (9-12 meV) than that without surfactant or oleic acid (17-21 meV), thus indicating improved charge transport and consequently an increased short-circuit current. Furthermore, the impedance characteristics showed that the injection resistance, when the BQ surfactant was used, was lower than that when no surfactant or oleic acid was used. These experiments provide further evidence that the use of semiconducting surfactants is essential to improve the performance of hybrid bulk heterojunction solar cells.

Structural, optical, dielectric and magnetic properties of CaFe2O4 nanocrystals prepared by solvothermal reflux method

Single crystalline CaFe2O4 nanospheres were synthesized by solvothermal reflux method using high boiling point organic solvents mixture. Both X-ray diffraction and electron diffraction profiles were confirmed single phase nature of the compound. The sample shown spherical morphology with average particle size of 10 nm which is same as crystallite size determined from the XRD. A thin layer of surfactant oleic acid was adsorbed on the surface of the nanoparticles. The optical excitation spectra reveals that the compound has direct allowed energy bandgap of 1.26 eV. The temperature dependent dielectric constant (εr′) and dielectric loss (εr″) measurements show low values at room temperature and were nominally changes with enhance of temperature upto 650 K. Above which both εr′ and εr″ were steeply increased with small variation of temperature which could be assigned to enhanced electrical conductivity due to surface charge conduction and, partially, to on-set of decomposition of oleic acid present on the surface of the sample. The samples show variable electron hopping conductivity in the temperature range studied and was supported by both Arrhenius plots and electric modulus studies at different frequencies. The CaFe2O4 nanoparticles show superparamagnetic nature at room temperature with high saturation magnetization (48.54 emu/g). The magnetization is much higher than ferrimagnetic bulk magnetization. Langevin function fit to magnetization data give 8 nm magnetic domain diameter and 1 nm magnetically disordered thin shell on the surface of the nanoparticles. As CaFe2O4 nanoparticles were electrically resistive and low dielectric loss materials, they may find applications in microwave engineering. In addition, the CaFe2O4 superparamagnetic nanoparticles were biocompatible and have high saturation magnetization, they could be used in biomedical applications such as magnetic hyperthermia and directed drug delivery applications.

Experimental investigation on the stability and abrasive action of cerium oxide nanoparticles dispersed diesel

Ceria nanoparticle is a well-known fuel borne additive for reducing the particulate emissions from diesel engines. Main challenges in the use of ceria nanoparticles are the lack of long-term dispersion stability in diesel and their effect on lubricity of diesel. The present work mainly focuses on synthesis of stable ceria nanoparticle diesel suspension and study on their lubricity. Ceria nanoparticles were synthesized by co-precipitation method and nano fluids were prepared by two-step method. The optimum concentration of oleic acid (surfactant) was determined based on critical micelle concentration studies and concentration of ceria nanoparticle in diesel was varied from 5 to 25 ppm. Long term dispersion stability studies using Dynamic light scattering system and Turbidity meter shows 10 ppm as an optimum concentration of ceria nanoparticle in diesel for maximum stability. Tribological properties of modified diesel were studied by a standard pin on disk apparatus. The wear rate was found to be reduced for all the nano additive concentrations in diesel and was least for 15 ppm. Based on studies conducted, 10 ppm is reported as an optimum concentration of nanoparticle in diesel having both enhanced stability and lubricity as compared to other concentrations of ceria nanoparticles in diesel.

Cleaning of magnetic nanoparticle surfaces via cold plasmas treatments

We report surface cleaning of magnetic nanoparticles (SmCo5 nanochips and CoFe2O4 nanoparticles) by using cold plasma. SmCo5 nanochips and CoFe2O4 nanoparticles, coated with surfactants (oleic acid and oleylamine, respectively) on their surfaces, were treated in cold plasmas generated in argon, hydrogen or oxygen atmospheres. The plasmas were generated using a capacitively coupled pulsed radio frequency discharge. Surface cleaning of nanoparticles was monitored by measurement of the reduction of surface carbon content as functions of plasma processing parameters and treatment times. EDX and XPS analyses of the nanoparticles, obtained after the plasma treatment, revealed significant reduction of carbon content was achieved via plasma treatment. The SmCo5 nanochips and CoFe2O4 nanoparticles treated in an argon plasma revealed reduction of atomic carbon content by more than 54 and 40 in atomic percentage, compared with the untreated nanoparticles while the morphology, crystal structures and magnetic properties are retained upon the treatments.

Ni nanoparticles prepared by simple chemical method for the synthesis of Ni/NiO-multi-layered graphene by chemical vapor deposition

A new chemical method was used to obtain a high yield of nickel nanoparticles (Ni-NPs). The effect of solvent (distilled water, ethylene glycol, and ethanol) and surfactant (oleic acid and polyvinyl pyrrolidinone) on the morphology and crystallinity of the synthesized Ni-NPs has been investigated. The experimental results revealed that among the solvents mentioned above, ethanol gives the best results in terms of complete reduction, controlled morphology and size distribution of Ni-NPs. The surfactants played an important role in impeding the agglomeration and surface oxidation of Ni-NPs. The surfactants also affected the morphology of the Ni-NPs. The synthesized Ni-NPs are found to be quite stable in air. The best of the synthesized Ni-NPs were effectively used as catalysts for the synthesis of Ni/NiO-multi-layered graphene using catalytic chemical vapor deposition technique.

Facile synthesis of water‐dispersible magnetite nanorings from surfactant‐free hematite nanorings

Surfactant-free α-Fe2O3 nanorings (NRs) were directly converted into water-dispersible Fe3O4 NRs through a simple and straightforward approach. In this process, uniform α-Fe2O3 NRs obtained through hydrothermal synthesis method are firstly thermally reduced to hydrophobic Fe3O4 NRs in the presence of hydrophobic oleic acid surfactant and non-polar trioctylamine solvent (under a flow of 5% H2/95% Ar). Subsequently, oxidative cleavage of oleic acid capping agent using sodium periodate oxidising agent is imparted to yield water-dispersible Fe3O4 NRs. As compared with the traditional solid-state reduction in tube furnace, the obtained Fe3O4 NRs using solution-based reduction process can retain its original uniform ring shape with good crystallinity and well-defined magnetic vortex domain. Moreover, with the presence of azelaic acid on the surface of hydrophilic Fe3O4 NRs, antibody or drugs can be easily conjugated, which further boost its potential theranostics application. This work provides a convenient approach to convert surfactant-free nanoparticle (NP) powders into water-dispersible NPs colloidal solutions for various biomedical applications.

Experimental study on the thermo-physical properties of car engine coolant (water/ethylene glycol mixture type) based SiC nanofluids

The engine coolant (water/ethylene glycol mixture type) becomes one of the most commonly used commercial fluids in cooling system of automobiles. However, the heat transfer coefficient of this kind of engine coolant is limited. The rapid developments of nanotechnology have led to emerging of a relatively new class of fluids called nanofluids, which could offer the enhanced thermal conductivity (TC) compared with the conventional coolants. The present study reports the new findings on the thermal conductivity and viscosity of car engine coolants based silicon carbide (SiC) nanofluids. The homogeneous and stable nanofluids with volume fraction up to 0.5vol.% were prepared by the two-step method with the addition of surfactant (oleic acid). It was found that the thermal conductivity of nanofluids increased with the volume fraction and temperature (10–50°C), and the highest thermal conductivity enhancement was found to be 53.81% for 0.5vol.% nanofluid at 50°C. In addition, the overall effectiveness of the current nanofluids (0.2vol.%) was found to be ~1.6, which indicated that the car engine coolant-based SiC nanofluid prepared in this paper was better compared to the car engine coolant used as base liquid in this study.

Transport of a partially wetted particle at the liquid/vapor interface under the influence of an externally imposed surfactant generated Marangoni stress

Marangoni flows offer an interesting and useful means to transport particles at fluid interfaces with potential applications such as dry powder pulmonary drug delivery. In this article, we investigate the transport of partially wetted particles at a liquid/vapor interface under the influence of Marangoni flows driven by gradients in the surface excess concentration of surfactants. We deposit a microliter drop of soluble (sodium dodecyl sulfate) aqueous surfactant solution or pure insoluble liquid (oleic acid) surfactant on a water subphase and observe the transport of a pre-deposited particle. Following the previous observation by Wang et al. [1] that a surfactant front rapidly advances ahead of the deposited drop contact line and initiates particle motion but then moves beyond the particle, we now characterize the two dominant, time- and position-dependent forces acting on the moving particle: (1) a surface tension force acting on the three-phase contact line around the particle periphery due to the surface tension gradient at the liquid/vapor interface which always accelerates the particle and (2) a viscous force acting on the immersed surface area of the particle which accelerates or decelerates the particle depending on the difference in the velocities of the liquid and particle. We find that the particle velocity evolves over time in two regimes. In the acceleration regime, the net force on the particle acts in the direction of particle motion, and the particle quickly accelerates and reaches a maximum velocity. In the deceleration regime, the net force on the particle reverses and the particle decelerates gradually and stops. We identify the parameters that affect the two forces acting on the particle, including the initial particle position relative to the surfactant drop, particle diameter, particle wettability, subphase thickness, and surfactant solubility. We systematically vary these parameters and probe the spatial and temporal evolution of the two forces acting on the particle as it moves along its trajectory in both regimes. We find that a larger particle always lags behind the smaller particle when placed at an equal initial distance from the drop. Similarly, particles more deeply engulfed in the subphase lag behind those less deeply engulfed. Further, the extent of particle transport is reduced as the subphase thickness decreases due to the larger velocity gradients in the subphase recirculation flows.

Characterization of Nanoemulsion Prepared from Self-emulsifying Rifampicin and its Antibacterial Effect on Staphylococcus aureus and Stap. epidermidis Isolated from Acne

In this study, three different self emulsifying drug delivery systems of rifampicin (SEDD-R) were made using oleic acid and different surfactants such as Tween 80, Chremophor RH 40 and Chremophor EL designated as RN-TW, RN-CRH and RN- CEL. These self-emulsifying systems were converted to rifampicin nanoemulsion by adding water under sonication. The resulting particle sizes were found to be 192.7 nm, 183.4 nm and 179.2 nm for RN- CEL, RN-CRH and RN-TW, respectively using Zetasizer. Drug content, entrapment efficiency, in vitro drug release and pH stability tests was performed. Drug content and entrapment efficiency for RNTW, RN-CRH and RN- CEL were found as 0.9945% & 0.9835%, 0.9720% & 84.31% and 74.58 % & 56.89%, respectively. The release of drug from RN-TW, RN-CRH and RN-CEL occurred for 450-, 330- and 240- minutes, respectively. The pH stability study demonstrated that all formulations retained maximum drug at pH 5.8. Antibacterial effect of the preparations was evaluated against S. epidermidis and S. aureus isolated from acne and showed effective results.Dhaka Univ. J. Pharm. Sci. 14(2): 171-177, 2015 (December)

Magnetoviscous effect in ferrofluids with different dispersion media

Ferrofluids based on magnetite nanoparticles dispersed in different carrier media (dialkyldiphenyl and polyethylsiloxane) have been synthesized using mixed surfactants (oleic acid, stearic acid and alkenyl succinic anhydride). Magnetic properties of the samples and a change of their shear viscosities in an applied magnetic field have been studied in order to evaluate an influence of the carrier medium on a magnetoviscous effect. A significance of the interaction of the carrier medium and surfactant with a consideration of the magnetic and rheological behavior of ferrofluids was demonstrated.

Heat transfer behaviour of silver particles containing oleic acid surfactant: application in a two phase closed rectangular cross sectional thermosyphon (RTPTC)

This article focuses on heat transfer behaviour of silver nanoparticles containing oleic acid surfactant (OA) applied as a working fluid in a two-phase closed rectangular cross sectional thermosyphon (RTPTC). Thus, the OA could reduce the surface tension of the working fluid, which improved the colloidal ability and increased the lead-time period for nanoparticles to be uniformly dispersed. It highlights theories for investigating the effects on heat transfer characteristics of RTPTC such as heat transfer rate, thermal resistance, heat transfer coefficients and nanofluids behaviour. The most important heat transfer characteristic to be examined in this experiment is the relative thermal efficiency (RT). Five working fluids were tested, these include: de-ionized water; de-ionized water base with a silver nanoparticles concentration of 0.5 wt% (NP); and NP containing 0.5; 1; and 1.5 wt% of OA respectively. The results showed that 0.5 wt% NP containing 1 wt% OA produced the best results. It was further found that the heat transfer rate of 0.5 wt% NP containing 1 wt% of OA with a RT value of 1, was the highest across all experimental parameters studied. The NP containing OA demonstrated approximately 80 % higher heat transfer rate than the de-ionized water.

Extreme pressure properties of nanolubricants for metal-forming applications

Purpose – The purpose of this paper is to evaluate the extreme pressure properties of CuO and TiO2 nanoparticle additives with the incorporation of a surfactant within a synthetic fluid for metal-forming applications. Design/methodology/approach – The paper studies the effect of CuO and TiO2 nanoparticle additives at various concentrations (0.01, 0.05 and 0.10 wt. per cent) in a synthetic lubricant fluid under extreme pressure conditions. Oleic acid surfactant is added to the nanolubricant to improve dispersion and stability of nanoparticles. Extreme pressure tribological tests are performed on a four-ball T-02 tribotester according to the ITEePib Polish method for testing lubricants under conditions of scuffing. Findings – The results show that the addition CuO and TiO2 nanoparticles under the presence of OA resulted in an increase of the load-carrying capacity (poz) of the lubricant up to 137 and 60 per cent, respectively. The seizure load was also increased by 50 and 15 per cent, respectively. Practical implications – The results show that CuO and TiO2 nanoparticles can be successfully used as additives improving extreme pressure properties of lubricants. Originality/value – This demonstrates the potential of nanoparticle additives using surfactants for improving the extreme pressure properties of lubricants. These nanolubricants can be used for metal-forming applications like deep-drawing, achieving an increased tool life.

Rheological measurement of redispersibility and settling to analyze the effect of surfactants on MR particles

The smart materials such as magnetorheological (MR) fluids are gaining wide popularity due to their superior control abilities. These abilities are strongly dependent about the stability of the MR fluid which needs to be sustained for the useful life of the system. In the present research work, experimental studies focusing on aggregation, redispersibility and settling of carbonyl iron-based MR fluids have been conducted to analyze the effect of surfactants on controlling settling and redispersibility. The experimental investigations were conducted by preparation of nine MR fluids samples using three types of surfactants (oleic acid, citric acid and tetramethylammonium hydroxide) and three different carrier fluids (water, silicone oil and DTE light mineral oil). The samples were prepared by mixing on rotational machine for 24 h and the homogeneity of the samples was visually inspected. The shear stress and viscosity variation of the homogenous mixture with respect to shear rate was obtained using magnetic rheometer. A new method is presented for measuring the settling of homogenous mixtures by measurement of the change in the magnetic field strength due to settlement of particles. The effect of surfactant type and its quantity on the stability of MR fluid is explored and the results of settling and redispersibility have been presented.

Thermal conductivity, viscosity and stability of Al2O3-diathermic oil nanofluids for solar energy systems

Nanofluids have excellent potentiality in the field of heat transfer fluids and particularly for solar energy systems such as concentrated solar power plants. However they present many issues to be fixed in order to have a large diffusion. One of these is sedimentation. In this paper, stability, viscosity, FT-IR spectra, cluster size and thermal conductivity of Al2O3 – Therminol nanofluids have been investigated as heat transfer fluid in high temperature solar energy systems.Al2O3 – Therminol nanofluids have been prepared to investigate and to improve stability of the suspensions, varying temperature during mixing with magnetic stirrer, amount of surfactant and sonication time with ultrasonic vibrator. Stability of the nanofluid samples was investigated through backscattering technique and for cluster size analysis Dynamic Light Scattering (DLS) was used. Thermal conductivity of the sample was measured in order to evaluate not only the effect of both volume fraction and temperature, but also the influence of the surfactant (oleic acid).Stability of nanofluids depends on temperature during sample preparation and sedimentation phenomenon is inversely proportional to temperature during mixing with magnetic stirrer.Influence of concentration of surfactants was studied through preparation of samples having a solid phase particles concentration of 0.3%vol, 0.7%vol and 1.0%vol, respectively. The presence of surfactants creates some bonds with nanoparticles, which mainly helps nanofluids long-term stability. On the other hand, the presence of surfactants inside the nanofluids does not influence their thermal conductivity. From DLS measurements, a dependence of cluster size on volume fraction was observed for all nanofluid samples. Experimental data showviscosity increases by increasing volume concentration; nanofluids with and without surfactants show a non-Newtonian behavior and viscosity of nanofluids increases by increasing cluster size.

Optimizing Synthesis of Maghemite Nanoparticles as an Anode for Li-Ion Batteries by Exploiting Design of Experiment

The synthesis of iron oxide nanoparticles via coprecipitation was studied by exploiting a factorial design of experiment methodology to investigate the influence of pH, medium temperature, Fe3+/Fe2+ ratio, and reaction time on the crystallite size. X-ray diffraction revealed that crystallite size decreased with increased pH and the Fe3+/Fe2+ ratio more significantly. This approach enabled us to make a reliable and reproducible protocol for optimizing the synthesis of monodispersed maghemite nanoparticles. Fourier transform infrared spectra and simultaneous thermal analysis results suggested the coexistence of two kinds of binding energies between surfactant (oleic acid) molecules and the maghemite nanoparticles. Brunauer–Emmett–Teller surface area and high-resolution transmission electron microscope results disclosed that the average particle size of the optimized sample was around 8 nm. Galvanostatic charge–discharge cycling for the optimized sample, and the sample with average particle size of 19 nm showed reversible capacities of 430 mAh g−1 and 340 mAh g−1 at 500 mA g−1, respectively, which is attributed to the narrower size distribution and smaller particle size of the optimized sample.