Oleic Acid Molecules Research Articles

The Biomimetic System of Oleanolic Acid and Oleic Acid at the Air-Water Interface-Interactions in Terms of Nanotechnology-Based Drug Delivery Systems.

Oleanolic acid (OLA) and oleic acid (OA) are ubiquitous in the plant kingdom, exhibiting a therapeutic effect on human health, and are components of novel pharmaceutical formulations. Since OLA has limited solubility, the utilization of nanotechnology-based drug delivery systems enhancing bioavailability is highly advantageous. We report on the interfacial behavior of the OLA:OA system at various molar ratios, using the Langmuir technique to assess the dependence of the molar composition on miscibility and rheological properties affecting film stability. Specifically, we evaluate the interfacial properties (morphology, thermodynamics, miscibility, and viscoelasticity) of the OLA:OA binary system in various molar ratios, and indicate how the OLA:OA system exhibits the most favorable molecular interactions. We apply the Langmuir monolayer technique along with the complementary techniques of Brewster angle microscopy, dilatational interfacial rheology, and excess free energy calculations. Results demonstrate that the properties of mixed monolayers depend on OLA:OA molar ratio. Most of the systems (OLA:OA 2:1, 1:1, 1:5) are assumed to be immiscible at surface pressures >10 mN/m. Moreover, the OLA:OA 1:2 is immiscible over the entire surface pressure range. However, the existence of miscibility between molecules of OLA and OA in the 5:1 for every surface pressure tested suggests that OA molecules incorporate into the OLA lattice structure, improving the stability of the mixed film. The results are discussed in terms of providing physicochemical insights into the behavior of the OLA:OA systems at the interface, which is of high interest in pharmaceutical design.

Yellow-light emitted single halide CsPbI3 nanowire

With the rapid development of metal halide perovskite, reducing its dimensionality into two-dimensional (2D) or one-dimensional (1D) nanostructures has been reported to be a good alternative for expanding the spectral absorption or emission range. For example, when substituting monovalent cation Cs+ with phenylethylammonium (PEA+) on fabricating 2D-CsPbI3, the photoluminescence peak processes a maximum regulation from 710 to 625 nm. Simultaneously, when slicing into 1D CsPbI3 nanowires, the light emission could also achieve a maximum blue shift from 700 to 600 nm. Herein, by using a ligand-assistant reprecipitation (LARP) method, oleic acid (OA) molecule is successfully inserted into the lattice of one-dimensional CsPbI3 nanowire (namely OA-CsPbI3), which presents a monochromatic yellow light emission at 558 nm with narrow emission-band (about 28 nm), and records high photoluminescence quantum yield (PLQY) of 94%. Such a yellow-light emission in single halide CsPbI3 systems has never been discovered before. Meanwhile, a shallow energy level in the OA-CsPbI3 nanowire is further identified by the ultrafast transient absorption (TA) and first-principle calculation, which helps the photoexcited carriers bypass the trap state level in the bandgap and enhances the radiative excitons lifetime with maximum binding energy up to 212.5 meV. What's more, the excellent thermal and moisture stabilities of the newly formed one-dimensional OA-CsPbI3 nanowire indicate a promising application prospect in the field of luminescent devices.

Reversible, voluminous and tunable patterning of multiwalled carbon nanotubes in ferrofluid: Partial or complete?

A new kind of hybrid fluids showing multiwalled carbon nanotubes (MWCNTs) coupled with magnetic nanoparticles have been synthesized and investigated for their structural, magnetic, and magneto-viscoelastic properties. The experimental results confirmed the cooperative coupling between MWCNTs and Fe3O4 nanoparticles forming the basis of magnetorheological mechanism which narrates the rheological properties. The molecular dynamics (MD) simulation and interaction calculations for particle-particle, particle-tube and tube-tube have been described and explained comprehensively in view of the interface properties of nanoparticles and nanotubes. The whole of the experimental and theoretical investigations confirms the bulk alignment of bent MWCNTs in ferrofluidic system which can be tuned with an applied magnetic field. The MD simulation predicts a weak and short-range molecular ordering mediated via free oleic acid molecules between MWCNTs and coated nanoparticles of ferrofluid. The interparticle interaction calculations (van der Waals, steric and magnetic energies) showed that the surface coated magnetic nanoparticles are kinetically stable in the fluid while the MWCNTs form chain-like aggregates. Moreover, by application of classical beam theory, a thermodynamic energy barrier comparison was made for the unbending of particle impregnated MWCNTs. Thus, considering the dimensional compatibility of nanotubes and nanoparticles, a field-induced partial alignment of MWNCTs by virtue of their bent form in ferrofluidic system is proposed. A partial or complete accomplishment of the reversibility and tunability of the patterning of MWCNTs on a large scale in ferrofluid has been investigated in detail.

Combining micro-infrared reflection absorption spectroscopy with density functional theory for investigating the adsorption of organic friction modifiers on steel surfaces

Friction plays a major role in contributing to the global energy consumptions and reducing it would bring about major economic and environmental advantages. Organic friction modifiers are cost-effective and environmentally friendly additives which are included in the lubricant packages to improve performances. Their friction-reducing properties are connected to their adsorption state on steel surfaces. This study applies Infrared Reflection Absorption Spectroscopy (IRRAS) to probe the oleic acid tribofilm on microscopic areas of the sample (micro-IRRAS). The recorded spectra are interpreted by density functional theory (DFT) calculations and provide useful information about the effect of the tribological phenomena on the adsorption state and molecular orientation of the oleic acid friction modifier. The oleic acid molecules adsorb on the surface forming both monodentate and bridging configurations on the iron atoms. IRRAS data show that under the effect of friction the molecules tilt towards the steel surface.

Changes in structures and digestibility of amylose-oleic acid complexes following microwave heat-moisture treatment

Amylose-oleic acid complexes (AOA) were exposed to microwave heat-moisture treatment (M-HMT) with different moisture content (MC), and the variations in structures and digestibility were investigated. M-HMT caused the dissociation of helical structures and destruction of short-range molecular order of AOA. Meanwhile, the molecules of amylose and oleic acid rearranged and more amylose-oleic acid complexes were formed during M-HMT, the complexing index of AOA was increased from 25.41 % to 41.20 % when treating at 35 % MC. Moreover, the relative content of single helix increased with increasing MC, resulting in higher V-type relative crystallinity. With ≥30 % MC, the treated complexes showed greater thermostability than that of original AOA. The treatment increased the enzymatic digestibility of AOA, and sample treated with 35 % MC had the highest resistant starch content of 82.33 %, which was 17.96 % higher than that of native AOA. The improved enzyme resistance should be correlated to increased molecular interplay and formation of amylose-oleic acid complexes.

Dynamic interfacial tensions of sulfobetaine and polymers solutions: Effect of structures

To facilitate the understanding of the intrinsic mechanism responsible for the IFTs of betaine solutions, partly hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM) were employed to investigate their effect on IFTs of different betaine solutions against decane using a spinning drop interfacial tensiometer. Moreover, the effects of oleic acid on the IFTs of betaine-polymer systems were also studied. The results show that the water-soluble polymers (HPAM) form the mixed adsorption film with alkyl sulfobetaine (ASB) molecules and prevent the hydrophilic groups of ASB from lying flat, which produces a minimum IFT with aging time. Besides, the hydrophobic HMPAM forms mixed micelle-like interfacial associations with ASB molecules, which results in a stronger disruption tendency for the interfacial film. The branched xylyl substituted alkyl sulfobetaine (BSB) molecules will form a tight interfacial film, therefore HPAM can’t insert into the interfacial film easily. Meanwhile, steric hindrance makes it difficult to form interfacial aggregates with HMPAM. Thus, the addition of HPAM and HMPAM polymers has little influence on the IFTs in the BSB system. The mixed adsorption of oleic acid and betaine molecules results in a significant decrease in IFTs, especially for BSB. However, in the ASB-polymer system, HPAM forms mixed adsorption film with ASB molecules and hinders the adsorption of oleic acid, accordingly IFTs change little. In contrast, the hydrophobic interaction of HMPAM promotes the adsorption of oleic acid, so the synergistic effect reduces IFTs to some extent. In the BSB-polymer system, the strong synergistic effect between oleic acid and BSB molecules is disrupted by polymers, which results in a significant increase in IFTs. The relevant results are helpful for the design of novel and efficient chemical flooding systems.

Molecular modeling, mutational analysis and steroid specificity of the ligand binding pocket of mPRα (PAQR7): Shared ligand binding with AdipoR1 and its structural basis

The 7-transmembrane architecture of adiponectin receptors (AdipoRs), determined from their X-ray crystal structures, was used for homology modeling of another progesterone and adipoQ receptor (PAQR) family member, membrane progesterone receptor alpha (mPRα). The mPRα model identified excess positively charged residues on the cytosolic side, suggesting it has the same membrane orientation as AdipoRs with an intracellular N-terminus. The homology model showed identical amino acid residues to those forming the zinc binding pocket in AdipoRs, which strongly implies that zinc is also present in mPRα. The homology model showed a critical H-bond interaction between the glutamine (Q) residue at 206 in the binding pocket and the 20-carbonyl of progesterone. Mutational analysis showed no progesterone binding to the arginine (R) 206 mutant and modeling predicted this was due to the strong positive charge of arginine stabilizing the presence of an oleic acid (C18:1) molecule in the binding pocket, as observed in the X-rays of AdipoRs. High Zn2+ concentrations are predicted to form a salt with the carboxylate group of the oleic acid, thereby eliminating its binding to the free fatty acid (FFA) binding pocket, and allowing progesterone to bind. This is supported by experiments showing 100 µM Zn2+ addition restored [3H]-progesterone binding of the Q206R mutant to levels in WT mPRα and increased [3H]-progesterone binding to mPRγ and AdipoR1 which have arginine residues in this region. The model predicts hydrophobic interactions of progesterone with amino acid residues surrounding the binding pocket, including valine 146 in TM3, which when mutated into a polar serine resulted in a complete loss of [3H]-progesterone binding. The mPRα model showed there is no hydrogen bond donor in the vicinity of the 3-keto group of progesterone and ligand structure-activity studies with 3-deoxy steroids revealed that, unlike the nuclear progesterone receptor, the 3-carbonyl oxygen is not essential for binding to mPRα. Interestingly, the small synthetic AdipoR agonist, AdipoRon, displayed binding affinity for mPRα and mimicked progesterone signaling, whereas D-e-MAPP, a ceramidase inhibitor, blocked progesterone signaling. Thus, critical residues around the binding pocket and steroid structures that bind mPRα, as well as similarities with AdipoRs, can be predicted from the homology model.

Study of the Electrical Conductivity of Magnetic Fluids

The effects of electrical conductivity of magnetic fluids (MFls) are investigated both in the presence and in the absence of an external magnetic field (MF). It is shown that in MFls based on magnetite (Fe3O4) magnetic nanoparticles (MNPs) coated with the surfactant – oleic acid (OA), conductive ions are formed by OA molecules in both dissociation and electro-chemical processes. The decisive role of electrochemical reactions of OA molecules on the surface of chemically active Cu electrodes, which form injection conductivity, has been proved. The analysis of the anisotropy of the MFl electrical conductivity in an external MF with chemically active and silent electrodes is given. An interpretation is present-ed of nonstationary ionic processes in the near-electrode layers which de-termine the kinetics of MNPs and autowaves in thin layers of MFLs.

Study on the pyrolysis mechanism of unsaturated fatty acid: A combined density functional theory and experimental study

In this study, oleic acid was used as a model compound to discuss the mechanism of thermal conversion of unsaturated fatty acids to hydrocarbons, so as to promote the goal of obtaining renewable chemicals and fuels from unsaturated fatty acids. In-situ detection techniques such as TG-FTIR and Py-GC/MS combined with density functional theory were applied to study the reaction mechanism of oleic acid molecules in the conditions of slow pyrolysis and fast pyrolysis. As the temperature rises, the hydrogen bond is broken, and the vibration peak of oleic acid shows obvious dehydrogenation under slow pyrolysis, and the same situation exists under fast pyrolysis. As the temperature increases, the pyrolysis process of oleic acid molecules changed from the dominant role of bimolecular mutual catalysis to that of free radical reaction. The results of Py-GC/MS showed that methyl, ethyl, and hydrogen radicals are the main active substances under the conditions of high temperature and fast pyrolysis of unsaturated fatty acid. This work demonstrates the feasibility of producing renewable hydrocarbons by pyrolysis of unsaturated fatty acids and proposed influenced factors to control product distribution. Novelty Statement Density functional theory (DFT) combined with experiments was used in present study to supplement the understanding of the pyrolysis mechanism of fatty acids in bio oil pyrolysis, and the control factors of controlling the distribution of fatty acid pyrolysis products were proposed.

Ligand exchange of SnO2 effectively improving the efficiency of flexible perovskite solar cells

Owing to the advantages of portability and flexibility, flexible perovskite solar cells have broad application prospects in the fields of portable wearable electronics and photovoltaic buildings. However, high temperature annealing process is often needed to improve the crystallinity and electron transport properties for electron transport layer, which restricts the development of flexible perovskite solar cells. In this work, well crystalline and monodisperse SnO2 nanocrystals are synthesized by facile solvothermal method with the assistance of oleic acid molecules. However, the presence of oleic acid molecules blocks the transportation of photogenerated electrons on account of the insulation of oleic acid molecules. To address the problem, the oleic acid ligands are ulteriorly peeled off by ligand exchange technique. Surprisingly, the resulted SnO2 electron transport layer exhibits superior electron extraction and transport capacity. The final power conversion efficiency comes to 17.96% from 13.71%.

Dynamics of Flat Barium Hexaferrite Particles in a Lyotropic Liquid Crystal

This paper describes the results of experiments on the magnetization of barium hexaferrite particles embedded in lyotropic liquid crystals. The carrier liquid crystal medium was an aqueous solution of a mixture of sodium lauryl sulfate and lauric acid in a ratio 2/1. Barium hexaferrite particles were stabilized with two layers of surfactant. The first layer consisted of oleic acid molecules. Second layer was a mix of sodium lauryl sulfate and lauric acid in a ratio 1/1. The process of particle magnetization was investigated by observing the effect of birefringence. The intensity of light passing through the system of crossed polaroids and the time of its establishment were measured depending on the magnitude of the magnetic field and the concentration of the components of the liquid crystal. It was found that the field dependence of the birefringence effect changes significantly depending on the concentration of the liquid crystal. In a concentrated solution in the liquid-crystalline phase, a significant enhancement of the birefringence effect is observed in weak fields. As the concentration of the solution decreases, the field dependence of the birefringence effect smoothly transforms into the curve for particles dispersed in water.

Adsorption mechanism of oleic acid on the surface of aluminum nanoparticle: ReaxFF molecular dynamics simulation and experimental study

The adsorption mechanism of oleic acid(OA) on the surface of aluminum(Al) nanoparticle was studied using ReaxFF molecular dynamics simulation. A surface-oxidized Al nanoparticle was constructed to simulate the single-molecule and multi-molecule adsorption processes of OA on the surface of Al nanoparticle. It was found that single OA molecule adsorbed on the surface of the Al nanoparticles through its –COOH group to form a carboxylate structure, thereby forming a chemical adsorption monolayer on the surface of Al nanoparticle. During the multi-molecule adsorption process, the chemical adsorption layer will become denser with the increase of initial density of OA in the system. When the initial density is large enough, excess OA molecules were adsorbed outside the chemical adsorption layer by physical adsorption and form a chemical-physical bilayer adsorption structure on the surface of the particles. The simulation results were verified by the adsorption layer thickness determined with XPS and the bonding structure detected with FTIR. The adsorption mechanism of OA on the surface of Al nanoparticle was found to changes from a chemical monolayer adsorption to a chemical-physical bilayer adsorption with the increase of OA concentration.

Novel long-chain aliphatic polyamide/surface-modified silicon dioxide nanocomposites: in-situ polymerization and properties

A new kind of long-chain aliphatic polyamide (PA1218) with a relatively low melting point, high molecular weight, and stable mechanical properties at humid conditions was successfully developed via a polycondensation reaction between 1,18-octadecanedioic acid and 1,12-diaminodecane. Additionally, oleic acid-surfaced modified silicon dioxide (SSD) was prepared and employed to improve the properties of PA1218 through in-situ polymerization. FT-IR spectra and TGA thermograms confirmed the successful surface modification of nanoparticles, and consequently, 5% substitution of surface hydroxyl groups of SiO2 nanoparticles with oleic acid molecules. Moreover, the thermomechanical and rheology tests revealed a significant improvement in nanocomposites’ properties compared to the pure PA1218; for instance, the tensile strength and storage modulus were increased by 22% and 40%, respectively in the sample containing 3% SSD nanoparticles. This improvement, along with SEM images, confirmed the uniform dispersion of SSD nanoparticles through the employed in-situ polymerization and excellent compatibility between inorganic and organic phases, which was achieved via surface modification. Finally, all the samples demonstrated a water uptake capacity of less than 0.6% attributed to the high methylene/amide ratio in their backbones, causing these newly developed nanocomposites to be notable candidates for specific engineering applications.

Defect induced luminescence from surface modified calcium fluoride nanoparticles for in-situ temperature monitoring of lubricating oil

The utilization of functional nano-additives provides us a novel research idea to deal with the in situ temperature sensing/monitoring of lubricating oil. In this work, monodispersed and luminescent calcium fluoride (CaF2) nanoparticles with surface modification were synthesized by a hydrothermal approach, which were employed as nano-additives for polyalphaolefin (PAO6) lubricating oil. Because of the surface modification of hydrophobic oleic acid molecule, the as-prepared CaF2 nanoparticles exhibited excellent oil solubility. The tribological results further suggested that after dispersing in PAO6 lubricating oil, the CaF2 nanoparticles could maintain its original friction and wear properties. In addition to the above basic characteristics for lubricating nano-additives, it was attractive to find that the as-synthesized CaF2 nanoparticles exhibited a doublet luminescence characteristic. The intensity ratio of the two emission peaks presented a nearly linear relationship to the surrounding temperature, which was also effective for CaF2 nanoparticles dispersed in PAO6 base oil. By comprehensive consideration of the oil dispersibility, tribological properties and temperature responsiveness, the as-synthesized CaF2 nanoparticles should be promising nano-additives for temperature monitoring of lubricating oil.

Study of the surface properties and particle-particle interactions in oleic acid-coated Fe3O4 nanoparticles

Magnetite (Fe3O4) nanoparticles coated with organic material are of considerable importance in various areas of engineering, as well as in biomedicine. Several papers show drastic changes in the magnetic properties related to the surface effects and the particle-particle interactions strength. However, there is no consensus about the origin or mechanisms that produce these changes, which could be different depending on the particle size and shape, coating efficiency and particle-particle interaction strength. Aiming to shed light on these issues, oleic acid (OA) coated Fe3O4 nanoparticles with different sizes were synthesized by a thermal decomposition method. Structural and microscopic results revealed Fe3O4 nanoparticles with good crystallinity and almost-spherical or polyhedral shapes depending on the solvent used for the synthesis. Infrared (FTIR) spectroscopy indicated OA molecules attached to the surface of Fe3O4 NPs via bidentate (chelating and/or bridging) bonds; meanwhile, thermogravimetric analysis confirmed the presence of weakly and strongly bonded OA molecules, suggesting a successful coating of Fe3O4 NPs. Magnetization (M) vs. magnetic field (H) curves are consistent with a core/shell structure formed by magnetite/defective magnetite (maghemite) phases, in consistency with FTIR spectroscopy. It was determined lower saturation magnetization values than that expected for bulk magnetite, which was assigned to the likely presence of a fraction of iron ions in low-spin (LS) states in the defective magnetite (maghemite) layer at the particles surface. The magnetic results evidence that depending on the amount of OA coating, it is possible to tune the particle-particle separation distance, avoid particles agglomeration and particle-particle interactions. The temperature dependence of magnetization reveals the presence of non-interacting and interacting NPs. Meanwhile, AC magnetic susceptibility measurements are consistent with those results and provide features related to superparamagnetic (SPM) behavior, assigned to the non-interacting NPs, and interacting SPM behavior, assigned to the interacting NPs, whose interaction strength is not enough to lead to a spin-glass like behavior.

Controlled synthesis of gadolinium fluoride upconversion nanoparticles capped with oleic acid or polyethylene glycol molecules via one-step hydrothermal method and their toxicity to cancer cells

Cancer is one of the major diseases that threaten human life. Upconversion nanoparticles (UCNPs) are one of the new nanomaterials that are expected to detect and treat cancer. One-step hydrothermal method can synthesize UCNPs with controllable physical and chemical properties and low biotoxicity. In this work, oleic acid (OA) and polyethylene glycol (PEG)–modified NaGdF4/GdF3:Yb,Er UCNPs were synthesized by one-step hydrothermal method. And the as-prepared UCNPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and by using superconductor quantum interference devices (SQUID). The cytotoxicity of the modified NaGdF4/GdF3:Yb,Er UCNPs was evaluated. The results show that OA-modified UCNPs are hexagonal NaGdF4 phase, and PEG-modified UCNPs is orthorhombic GdF3 phase respectively. The particle size of OA-modified and PEG-modified UCNPs is about 15 nm and about 30 nm, respectively. The modified UCNPs have good magnetic properties and strong upconversion luminescence properties (UCL), wherein PEG-modified UCNPs perform slightly better capabilities than those of OA-modified UCNPs. When the concentration of nanoparticles increased from 62.5 to 500 μg/mL, OA-NaGdF4:Yb,Er showed a certain cytotoxicity and exhibited dose-effect relationship. However, PEG-GdF3:Yb,Er did not display obvious cytotoxicity. Therefore, PEG-modified UCNPs may be more suitable for application in oncology field.

Dispersed liquid crystals as pH-adjustable antimicrobial peptide nanocarriers

HypothesispH-responsive nanocarriers have the potential to provide targeted delivery of antimicrobial peptides (AMPs) to sites of bacterial infection with typically abnormal pH levels in the body. However, the local pH of the infected sites varies substantially among different infection-related diseases, calling for the development of delivery systems capable of targeting local pathological conditions in an adjustable pH range. ExperimentsIn this study, a highly versatile pH-responsive nanocarrier platform, based on dispersions of oleic acid (OA) and glycerol monooleate (GMO) self-assemblies with the human cathelicidin AMP LL-37, was designed and characterized. FindingsA detailed pH-composition phase diagram was constructed from small angle X-ray scattering and cryogenic transmission electron microscopy data. In addition, the protonation state and apparent pKa of OA embedded in these nano-self-assemblies were investigated by electrophoretic mobility measurements at different pHs and found to be strongly dependent on nanocarrier composition. By varying composition of these nanocarriers, the apparent pKa of embedded OA molecules could be tuned from 7.8 to 6.3, shifting the range of nanocarriers' pH-response. The study advances our fundamental understanding of self-assembly and pH-responsiveness in lipid-peptide systems containing monounsaturated long-chain fatty acids. The results may guide the future design of highly adaptable nanocarriers for patient-optimized pH-targeted AMP delivery.

Altering model cell membranes by means of localized magnetic heating

Isolated iron oxide magnetic nanoparticles (MNPs), 12 nm in diameter, coated with oleic acid molecules as capping agents have been deposited by the Langmuir-Blodgett (LB) method onto a model cell membrane incorporating 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and Cholesterol (Chol) in the 1:1 ratio, which was also fabricated by the LB technique. Atomic Force Microscopy (AFM) experiments showed that the application of an alternating magnetic field results in the embedding of the MNPs through the phospholipidic layer. These experimental results reveal that the heating of individual MNPs may induce a local increase in the fluidity of the film with a large control of the spatial and temporal specificity.

Aqueous-Organic Phase Transfer of Iron Oxide@Iron Carbide Nanoparticles Using Amide-Amine Modified Oleic Acid

The advances of iron based magnetic nanoparticles are extensively increasing due to the number of sources related to the synthesis process, the control on the particle dispersion and the interactions of ferrofluids that can be provide with different surface modifications. The wide range of uses granted to them are based on the physical, chemical stability and interaction properties in the different yields of material science. In this work, ferromagnetic iron carbide@iron oxide core@shell nanoparticles were synthesized with hydrophobic nature. Water dispersity was controlled by modifying the surface with a synthesized molecule of oleic acid with ethylenediamine by bioconjugation reaction obtaining a conjugated amide-amine modified oleic acid coating 6 nm magnetic nanoparticles with the capacity of being water dispersable. The synthesized nanoparticles, with modified organic acid and surface modified nanoparticle were characterized by TEM, DLS, zeta potential, mass spectrometry, FTIR and NMR.

Interfacial interactions between oleic acid and betaine molecules at decane-water interface: A study of dilational rheology

The interfacial interactions between organic acid and betaine molecules play an important role in reducing interfacial tension (IFT). To deeply detect the arrangements of organic acid and betaine molecules at the interface, the dilational rheological properties of mixed adsorption films formed by oleic acid and octadecyl carboxyl betaine (18PC) or octadecyl sulfobetaine (18PS) were investigated using drop shape analysis method at the decane-water interface. The influences of aging time, oscillation frequency and surfactants concentration were detected. The experimental results show that the properties of 18PC and 18PS adsorption film are controlled by both the fast diffusion-exchange process between the bulk and the interface and the slow re-arrangement process in the interface. 18PC film is tighter than that of 18PS because the size of carboxyl is small than sulfonyl. Oleic acid and betaine surfactants can form mixed adsorption films with less strength caused by the rapid transfer of oleic acid between the bulk and the interface, but more elastic due to the enhancement of the intermolecular interaction. In this case, the oleic acid molecules are easier to insert into the spaces between 18PS molecules on the interface, which results in a more tight mixed film than oleic acid/18PC film.