Arachidic Acid Monolayers Research Articles

Why Bubbles Coalesce Faster than Droplets: The Effects of Interface Mobility and Surface Charge.

Air bubbles in pure water appear to coalesce much faster compared to oil emulsion droplets at the same water solution conditions. The main factors explaining this difference in coalescence times could be interface mobility and/or pH-dependent surface charge at the water interface. To quantify the relative importance of these effects, we use high-speed imaging to monitor the coalescence of free-rising air bubbles with the water-air interface as well as free-falling fluorocarbon-oil emulsion droplets with a water-oil interface. We measure the coalescence times of such bubbles and droplets over a range of different water pH values (3.0, 5.6, 11.0). In the case of bubbles, a very fast coalescence (milliseconds) is observed for the entire pH range in pure water, consistent with the hydrodynamics of fully mobile interfaces. However, when the water-air interface is immobilized by the deposition of a monolayer of arachidic acid, the coalescence is significantly delayed. Furthermore, the coalescence times increase with increasing pH. In the case of fluorocarbon-oil droplets, the coalescence is always much slower (seconds) and consistent with immobile interface coalescence. The fluorocarbon droplet's coalescence time is also pH-dependent, with a complete stabilization (no coalescence) observed at pH 11. In the high electrolyte concentration, a 0.6 M NaCl water solution, bubbles, and droplets have similar coalescence times, which could be related to the bubble interface immobilization at the late stage of the coalescence process. Numerical simulations are used to evaluate the time scale of mobile and immobile interface film drainage.

Влияние температуры на формирование ленгмюровских монослоев с наночастицами Ni-арахиновой кислоты и кластерами Ni-арахидата

The effect of the subphase temperature on the formation of nickel arachinate clusters under a monolayer of arachidic acid was studied. The subphase temperature varied in the range from 10° to 30°C with a step of 4°C. The influence of temperature on the compressibility of the monolayer and the area occupied by one molecule in the Langmuir monolayer of nickel araquinate is demonstrated. The effect of temperature on the morphology of Langmuir-Blodgett films formed on their basis was also studied. It was found that, as the temperature changes, the number of nickel clusters increases and their sizes decrease. This is due to a change in the rate of growth and dissolution of clusters with a change in temperature. The distribution of clusters in the resulting film was random, however, they can be structured using external magnetic fields. Using the magnetic properties of NiArch clusters will make it possible to purposefully change the film structure by an external magnetic field. The results obtained are of great importance for practical applications in the creation of multilayer composite coatings with controlled magnetic properties. These films can be further used as touch coatings for acoustic and electronic sensors.

A study of the local atomic structure the environment of zinc ions of different concentrations during their interaction with the arachidic acid Langmuir monolayer

Vital cellular processes depend on the controlled transport of metal ions across biological membranes. A biological membrane is a complex system consisting of lipids and proteins, that is why simplified systems, in particular monomolecular layers, are used to model it. This work presents the results of a study of the interaction of zinc ions from the aqueous subphase with the Langmuir monolayer of arachidic acid. The study was carried out for the first time and used total external reflection X-ray absorption spectroscopy. It considers the influence of the concentration of a ZnCl2 aqueous subphase solution on the local environment of zinc ions when interacting with the lipid monolayer immediately after its formation. The theoretical analysis of experimental XANES spectra showed that one of the interaction ways of arachidic acid molecules with zinc ions immediately after the monolayer formation is an intramolecular interaction with the formation of spodium bonds between the zinc cation and the OH carboxyl group of arachidic acid

Role of Sn(II) in Mediating the Formation and Organization of a Langmuir Monolayer.

The influence of the Sn(II) ion on the formation and morphology of an arachidic acid (AA) monolayer was investigated using Langmuir film formation technology, pressure-area (Π-A) isotherm measurements, and Brewster angle microscopy (BAM). Our findings indicate that AA Langmuir monolayers exhibit organization that depends on subphase pH and Sn2+ concentration. There are multiple equilibria that are relevant to the complexation of AA monolayers, and the balance of Sn(OH)n equilibria and Sn(AA)n equilibria gives rise to unusual monolayer structural effects. With Sn2+ in the subphase, the AA monolayer exhibits an isotherm characterized by the absence of a collapse point and with a pH-dependent change in isotherm shape not consistent with the formation of an ordered solid phase. The amphiphile headgroup equilibrium mediates the absence of collapse seen experimentally and the ability of the monolayer to retain organization at a surface pressure of ca. 70 mN/m. BAM images show that the morphology of the monolayer depends on the Sn2+ concentration, consistent with several species of Sn(AA)n, where n = 1, 2, or 3, contributing to the overall monolayer order.

Formation and phase behavior of porphyrin/arachidic acid mixed systems and morphology study of Langmuir-Schaefer thin films

ABSTRACT The paper is focused on the study of the dynamic surface properties of mixed monolayers of porphyrin and arachidic acid with various mole fractions at the air–water interface. The choice of porphyrin solid thin film as an object of study is explained by its high potential application in the area of photovoltaics and medicine. The Langmuir monolayers of porphyrin and arachidic acid were formed under different conditions using the Langmuir-Blodgett technique. The increase of subphase temperature led to a decrease in the rigidity of the porphyrin monolayer and leads to accelerating the relaxation process of the monolayer. The chosen surface pressure (4, 5, 15 and 35 mN/m) affected the stability of the floating monolayer. The higher miscibility of the monolayers was obtained at the mole fraction of porphyrin = 0.333. The change in the phase of monolayers surface was reported on the basis of surface potential data. The morphology properties of the mixed systems transferred on silicon substrates by Schaeffer method are studied.

Diamond-rich crystalline nanosheets seeded with a Langmuir monolayer of arachidic acid on water.

The enigmatic self-assembling ability of nanodiamond (ND) particles has been discovered herein. Diamond-rich crystalline nanosheets with thickness of approximately ∼25 nm were grown from a Langmuir monolayer of arachidic acid (AA) at the interface between air and a dilute aqueous ND solution. Their fine rectangular shapes with uniform uniaxial birefringence indicate appreciable crystallinity, thus supporting that they are hydrated colloidal crystals of homogeneous ND particles.

Morphology of Mixed Langmuir and Langmuir-Schaefer Monolayers with Covered CdSe/CdS/ZnS Quantum Dots and Arachidic Acid.

The process of formation of a Langmuir-Schaefer (LS) matrix based on a mixed monolayer of arachidic acid (AA) and 8 nm CdSe/CdS/ZnS quantum dots (QDs) stabilized by molecules of trioctylphosphine oxide (TOPO) was investigated. The change in the morphology, monolayer compressibility, and area per elementary cell of the created mixed monolayers, depending on the ratio of the components, was studied. It is shown that the change in the morphology of Langmuir-Blodgett (LB) monolayers begins to occur at a ratio between the number of QDs and AA molecules of 1:24. Dendrimeric structures with a thickness of the order of 30-40 nm appear in the mixed monolayer when LB film deposition was carried out above the collapse surface pressure of a Langmuir film from only TOPO-covered QDs. Information on the dependence of the morphology of such structures on the molar ratio of the components is necessary for the production of ordered 2D nanostructures containing 0D and 1D objects with quantum bonds. Such nanostructures can be used in nanoelectronic and optoelectronic devices as a sensitive sensor element. The obtained results would be relevant for any type of spherical shape nanoparticles.

Spectroscopic Analysis of Cu(II)-Complexed Thin Films to Characterize Molecular-Level Interactions and Film Behavior.

We report on the structure and dynamics of a Cu2+-complexed arachidic acid (AA) monolayer formed by Langmuir-Blodgett (LB) deposition. Infrared reflection-absorption spectroscopy (IRRAS) was used to characterize aliphatic chain -CH2 symmetric and asymmetric stretching modes and determine the chain tilt angle and order as a function of subphase pH. Monolayer structure is controlled by metal ion-amphiphile interactions. At low subphase pH (<5), film buckling at high surface pressure is observed, while for high subphase pH (≥5), monolayer buckling is not observed. This finding is correlated to monolayer structural mediation by metal ion-amphiphile interactions. Dynamics and mobility of a fluorophore incorporated into the monolayer were also affected by Cu2+-AA interactions, determined by fluorescence recovery after photobleaching (FRAP) measurements. These data are consistent with the formation of a rigid film due to Cu2+ coordination to AA headgroups, with the extent of headgroup protonation being determined by the pH of the subphase during monolayer deposition.

Lipid-matrix effects on tyrosinase immobilization in Langmuir and Langmuir-Blodgett films.

The immobilization of the enzyme tyrosinase (Tyr) in lipid matrices can be explored to produce biosensors for detecting polyphenols, which is relevant for the food industry. Herein, we shall demonstrate the importance of the lipid composition to immobilize the enzyme tyrosinase in Langmuir-Blodgett (LB) films. Tyr could be incorporated into Langmuir monolayers of arachidic acid (AA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG), having as the main effect an expansion in the monolayers. Results from polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) pointed to electrostatic interactions between the charged residues of Try and the lipid headgroups, in addition to changes in the order of lipid chains. The interaction between Tyr and DPPC in Langmuir monolayers can be correlated with the superior performance of DPPC/Tyr LB films used as biosensors to detect catechol by cyclic voltammetry. The molecular-level interactions assessed via PM-IRRAS are therefore believed to drive an immobilization process for Tyr in the lipid LB matrix and may serve as a general criterion to identify matrices that preserve enzyme activity.

Formation of Gibbs and Langmuir floating layers based on copper nanoparticles: temperature and concentration effects

This paper is devoted to study of the formation of Gibbs floating layers from aqueous solutions of copper nanoparticles (Cu NPs) stabilized by the sodium dodecyl sulfate surfactant. Langmuir floating layers of arachidic acid formed on the surface of a water subphase containing Cu NPs were also studied. Adsorption of copper nanoparticles on a monolayer of arachidic acid at different conditions has been investigated. In the experiments the amount of copper nanoparticles in the subphase and the temperature of the subphase were changed. The performed analysis showed that the increase of subphase temperature from 29 to 42 °C leads to the increase of the area occupied by Langmuir floating layers in a liquid-condensed state by 30 and 32 %, respectively. After a single transfer of the floating layer onto the highly oriented pyrolytic graphite substrates, their surface microrelief was investigated by atomic force microscopy (AFM). The AFM scans showed that the obtained copper nanoparticles films contained separate areas with copper particles and their aggregates. With an increase of surface pressure from 10 to 40 mN/m, an increase of the height difference of the surface microrelief from 4 to 7 nm and an increase of the large aggregates number with lateral dimensions about 100 nm were observed.

Effects of Cu(II) on the Formation and Orientation of an Arachidic Acid Langmuir-Blodgett Film.

The influence of the copper(II) ion on the formation, morphology, and organization of an arachidic acid monolayer was investigated using Langmuir-Blodgett (LB) monolayers, Π-A isotherms, and Brewster angle microscopy (BAM). Our findings indicate that a Cu2+-complexed LB film exhibits an order that depends on the subphase pH, analogous to other metal ions. Yazdanian , M. ; et al. Ionic Interactions of Fatty Acid Monolayers at the Air-Water Interface . Langmuir 1990 , 6 , 1093 - 1098 . Kurnaz , M. L. ; et al. Morphology of Microphase Separation in Arachidic Acid-Cadmium Arachidate Langmuir-Blodgett Multilayers . J. Phys. Chem. 1996 , 100 , 11113 - 11119 . The metal ion facilitates the formation of solid-phase films at surface pressures as low as 5 mN/m. The films exhibit a rigid, ordered phase, evidenced by the absence of a collapse point and an increase in surface pressure rather than the typical sharp decrease in surface pressure, indicative of film failure. Amphiphile ionic charge vs pH (i.e., the extent of arachidic acid protonation) plays a role in the observed absence of collapse and the ability of the films to maintain order and cohesion at high surface pressures (ca. 65 mN/m). Additionally, film thickness data suggest that the incorporation of Cu2+ ions induces a change in orientation of the aliphatic chains of the amphiphiles and that amphiphile solubility in the subphase may play a role in the observed film behavior at low surface areas and high pH.

Molecular-Level Structure and Packing in Phase-Separated Arachidic Acid-Perfluorotetradecanoic Acid Monolayer Films.

Synchrotron-based X-ray scattering measurements of phase-separated surfactant monolayers at the air-water interface provide molecular-level structural information about the packing and ordering of film components. In this work, grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR) measurements were used to collect crystallographic structural information for binary mixed monolayers of arachidic acid (AA, C19H39COOH) with perfluorotetradecanoic acid (PA, C13F27COOH), a system that has previously been investigated using a variety of thermodynamic and micron-scale structural characterization methods. GIXD measurements at surface pressures of π = 5, 15, and 30 mN/m indicated that AA in pure and mixed films forms a rectangular lattice at π = 5 and 15 mN/m but a hexagonal lattice at π = 30 mN/m. PA formed hexagonal lattices under all conditions, with films being highly ordered and crystalline (as determined by Bragg peak width) at even the lowest surface pressures investigated. Phase separation occurred for all mixed monolayer film compositions and surface pressures, manifesting as diffraction peaks characteristic of the individual components appearing at different in-plane scattering vector qxy. For both pure and mixed films, the molecular tilt angle of the AA hydrocarbon chain toward the nearest-neighbor was substantial at low pressures but decreased with increasing pressure. The PA fluorocarbon chain showed negligible molecular tilt under all conditions, and was oriented normal to the subphase surface regardless of surface pressure or the presence of AA in the films. In all cases, the two components in the mixed film behaved entirely independently of film composition, which is exactly the expected result for a fully phase-separated, immiscible system. XR measurements of film thickness at the air-water interface supported these results; overall film thickness approached the calculated ideal surfactant tail lengths with increasing surface pressure, indicating nearly normal oriented surfactants. The overall surfactant packing and crystallographic features of the mixed monolayers are discussed in terms of the lipophobic nature of the perfluorinated surfactant as well as in context of thermodynamic miscibility and domain structure formation reported elsewhere in the literature for these mixed monolayer systems.

Study of Langmuir Monolayers of Arachidic Acid on Saline Solutions Using Sum-frequency Generation Vibrational Spectroscopy

Abstract: In this report, we studied the effect of halide salt concentration on Arachidic Acid (AA) Langmuir monolayers formed on salt solutions, such as NaCl, NaI, NaF by using a Sum-Frequency Generation Vibrational Spectroscopy. In the SFG spectra, we observed the peak intensities of CH3FR and CH3SS vibrational modes decreased when increasing the salt concentration. This observation indicates that the structure of the AA monolayer was disordered by the interaction of the dissolved ions with the carboxyl head groups of the monolayer.

Synthesis of graphene from naphthalene molecules on the surface of a Langmuir monolayer

This paper considers some approaches to the technology of the synthesis of a graphene monolayer at a phase interface. A surfactant monolayer on an aqueous subphase is proposed as the substrate for graphene synthesis. A monolayer is formed by the Langmuir–Blodgett method. Simple polyaromatic molecules, in particular, naphthalene, are considered as the basic substance for the synthesis of graphene. Arachidic acid is used as the basic surfactant molecule. To confirm the possibility of synthesizing graphene by the mentioned method, both experimental and theoretical studies are performed. In the course of experiemnts, it is shown that naphthalene molecules are pressed into the space above arachidic acid molecules upon the compression of monolayer of arachidic acid–naphthalene mixtures (such an assumption is made due to the characteristic value of the surface areas attributed to different phases of the monolayer and also to its characteristic parameters). The formation of a layer of naphthalene molecules on the surface of a monolayer is modeled by the molecular dynamics method (Amber potential). Different variants of the initial distribution of molecules are considered.

Photocatalytic oxidation of the organic monolayers on TiO2 surface investigated by in-situ sum frequency generation spectroscopy

In-situ vibrational sum frequency generation (SFG) spectroscopy has been employed to investigate the photocatalytic oxidation of two types of well-ordered organic monolayers, namely, an arachidic acid (AA) monolayer prepared by the Langmuir-Blodgett method and an octadecyltrichlorosilane (OTS) monolayer prepared by the self-assembling method, on a TiO2 surface under ultraviolet (UV) irradiation. The extremely high sensitivity and unique selectivity of the SFG spectroscopy enabled us to directly probe the structural changes in these monolayers during the surface photocatalytic oxidation and further elucidate their reaction mechanisms at a molecular level. It was revealed that the ordering of the monolayers during the photocatalytic reaction is strongly dependent on their interaction with the substrate; the AA monolayer maintains its ordered conformation until the final oxidation stage, while the OTS monolayer shows a large increase in disordering during the initial oxidation stage, indicating a different photocatalytic reaction mechanism of the two monolayers on the TiO2 surface.

Dynamics driven by lipophilic force in Langmuir monolayers: In-plane and out-of-plane growth.

While monolayer area fraction versus time (A(n)-t) curves obtained from surface pressure-area (π-A) isotherms for desorption-dominated (DD) processes in Langmuir monolayers of fatty acids represent continuous loss, those from Brewster angle microscopy (BAM) also show a two-dimensional (2D) coalescence. For nucleation-dominated (ND) processes both techniques suggest competing processes, with BAM showing 2D coalescence alongside multilayer formation. π enhances both DD and ND processes with a lower cutoff for ND processes, while temperature has a lower cutoff for DD but negligible effect on ND processes. Hydrocarbon chain length has the strongest effect, causing a crossover from DD to ND dynamics. Imaging ellipsometry of horizontally transferred films onto Si(100) shows Stranski-Krastanov-like growth for ND process in an arachidic acid monolayer resulting in successive stages of monolayer, trilayer, and multilayer islands, ridges from lateral island coalescence, and shallow wavelike structures from ridge coalescence on the film surface. These studies show that lipophilic attraction between hydrocarbon chains is the driving force at all stages of long-term monolayer dynamics.

Affinity separation by Langmuir–Blodgett deposition of bovine serum albumin using arachidic acid as specific ligand

Affinity separation by Langmuir–Blodgett (LB) deposition is a high resolution bioseparation procedure that takes advantage of the affinity between biomolecules and surface active materials, inducing the formation of a Langmuir-biofilm (L-biofilm) which is later removed from the air–water interface by deposition onto a solid substrate. This novel method is here applied to the separation of bovine serum albumin (BSA) by using arachidic acid (AA) as a ligand. Optimization of the experimental procedure choosing those conditions which favor Y-type multilayer deposition and low protein solubility is key. Both goals are achieved simultaneously by using Cd2+ as a counterion and a pH equal to the counterion pKA, that is pH=5.6. The selection of a target area of 22Å2/molecule, a value close to the footprint of AA in solid state, ensures that the protein will be squeezed out of the interface and bounded to the ligand. The transfer ratio (TR) values obtained during depositions for up to 6 layers show that the deposition was successful, and spectrophotometric analysis show that a 48% of the protein initially present at the subphase is removed. Additionally, the efficiency of separation for each layer is close to 100% with respect to the maximum amount of BSA that could fit in the film, assuming that the molecule stands vertically in the L-biofilm structure (long axis perpendicular to the solid). Atomic Force Microscopy (AFM) analysis qualitatively confirms the presence of the BSA in the deposited biofilm. The images illustrate that the presence of BSA strongly affects the topography of the surface, in the form of roughness and protrusions, unlike a pure arachidic acid monolayer. Roughness clearly increases when BSA is present in the deposited film. In summary, experimental evidence indicates the high potential of LB as a method for purification of proteins.

Three-Dimensional Analysis of the Collapse of a Fatty Acid at Various Compression Rates using In Situ Imaging Ellipsometry

The collapse of Langmuir monolayers of arachidic acid (AA) on water at various rates of molecular area compression has been investigated in situ by imaging ellipsometry (IE). The thickness of the collapsed AA molecules, which are inherently inhomogeneous, was determined by IE with a spatial resolution of a few microns. For the analysis, we determined the dielectric function of AA monolayers from 380 to 1690 nm by conventional spectroscopic ellipsometry. Compression rates ranged from 0.23 to $0.94{\AA}^2/min$ . A change of multilayer domains was observed in the in situ IE images. Lower compression rates resulted in more uniform collapsed films. Our experimental results correspond with previous theoretical simulations.

Different Adsorption Behavior of Rare Earth and Metallic Ion Complexes on Langmuir Monolayers Probed by Sum-Frequency Generation Spectroscopy

Adsorption behavior of counterions under a Langmuir monolayer was investigated by sum-frequency generation (SFG) spectroscopy. By comparing SFG spectra of arachidic acid (AA) Langmuir monolayer/water interface with and without added salt, it was found that the simple trivalent cation <TEX>$La^{3+}$</TEX> adsorbed on AA monolayer only when the carboxylic headgroups are charged (deprotonated), implying that counterion adsorption is induced by Coulomb interaction. On the other hand, metal hydroxide complex <TEX>$Fe(OH)_3$</TEX> adsorbed even on a charge-neutral AA monolayer, indicating that the adsorption of iron hydroxide is due to chemical interaction such as covalent or hydrogen bonding to the headgroup of the molecules at the monolayer.

Phase separation in mixed monolayers of arachidic acid and a phthalocyanine of zinc

Mixed Langmuir and Langmuir-Blodgett films of dissimilar components, arachidic acid and a phthalocyanine of zinc, have been investigated. These compounds form mixed films with phase separation, with domains at the sub-micro scale which are detected by AFM in LB films but not observed by BAM. These domains present different contrast in the surface potential images obtained with SP-AFM and in the friction images. The analysis of the isotherms and of the AFM images, at several compositions, reveals that the components are immiscible. The difference in height between the arachidic acid and the phthalocyanine of zinc phases is in accordance with the heights of the molecules, and points to the presence of a monolayer in the zinc phthalocyanine phase. AFM has revealed as a necessary technique to elucidate the miscibility in mixed films at the nanometric scale. UV–Vis spectroscopy shows changes in the spectra bands of LB films in respect to those in solution, due to the organization of the molecules in the LB film.