Langmuir Monolayer Films Research Articles

Surfactant micellar induced aggregation control of an anionic fluorescent dye in Langmuir-Blodgett film

This work reports the formation of stable Langmuir monolayer of an anionic water soluble fluorescent dye 5(6)-carboxyfluorescein (abbreviated as CFS) by electrostatic interaction with a cationic monolayer. Formation of non-fluorescent H-dimeric sites of CFS molecules in Langmuir monolayer and Langmuir Blodgett films has been controlled by using cationic surfactant micelles of cetyltrimethylammonium bromide (CTAB). Thus the film can act as efficient fluorescence marker. Langmuir monolayer has been investigated by Surface Pressure versus Area per molecule (π-A) isotherm and in situ Brewster Angle Microscope (BAM) studies. Mono and multilayered Langmuir Blodgett films were characterized by using UV–vis absorption and steady state fluorescence spectroscopy.

Two-dimensional synthesis of silver nanoparticle in situ Langmuir films from the reduction of silver sulfadiazine

Two–dimensional (2D) arrangement of monodisperse metallic nanoparticles (NPs) has attracted attention because of the unique properties of this assembly. These properties offer new perspectives for several applications. Thin film preparation techniques involve the synthesis of NPs through chemical methods and their subsequent attachment to various substrates based on different interactions. Langmuir–Blodgett (LB) technique is a promising method, which offers possibilities of in-situ preparation of metallic NP-structured and ordered monolayer films. In this study, 2D AgNPs were synthesized in situ through the reduction of a Langmuir monolayer consisting of a mixture of silver sulfadiazine (AgSD) molecules and stearic acid (SA) surfactant at the air-water interface. Two different Ag reduction methods were used. First, a NaBH4 aqueous solution was used as the subphase to react with the mixed Langmuir monolayer films. Second, the mixed films were irradiated by an ultraviolet (UV) light source (λ = 254 nm) for different time intervals. Scanning electron microscope images, energy-dispersive X-ray spectra, and contact angle measurements show that AgSD was an efficient precursor for the synthesis of Ag NPs LB films with long-range order. A small amount of SA is sufficient to cause the arrangement of the NPs, prevent their aggregation, and provide a hydrophobic characteristic to the Ag NPs LB films. Furthermore, the chemical reduction method using NaBH4 is better than the reduction under UV light for the synthesis of Ag NPs arrangement.

Effect of surfactant micelle on the fluorescence efficiency of a water soluble anionic xanthene dye in complex Langmuir-Blodgett (LB) film

Present communication reports the micellar effect on the increased fluorescence efficiency of a fluorescent dye in the complex LB film. In the complex Langmuir monolayer and Langmuir-Blodgett films, anionic Xanthene dye molecules organized differently when the films were prepared below and above the critical micellar concentration (CMC) of Cetyltrimethylammonium Bromide (CTAB) in the mixed solution of the Langmuir Trough. In-situ Brewster Angle Microscopic (BAM) studies showed the visual images of the Langmuir monolayers during the formation of the films. UV–Vis absorption and Fluorescence Spectroscopic studies were employed to study the spectral characteristics of the complex films.

Strain rate and temperature dependence of collapse pressure in Langmuir monolayer of cholesteryl dimers

We have synthesized two amphiphilic cholesteryl dimers, bis(cholesterylsuccinamidoethyl) ether [(NHSCE)2] and bis(cholesterylphthalamidopropyl) ether [(NHPCE)2]. They form stable Langmuir monolayer films at air-water interface. (NHSCE)2 exhibits only liquid condensed phase, whereas (NHPCE)2 exhibits both liquid expanded and liquid condensed phases. The collapse phenomenon of a Langmuir monolayer has relevance to biological processes like control of surface tension in lung alveolar and so on. Our studies show that the collapse pressure (πc) of (NHPCE)2 Langmuir monolayer is invariant with the strain rate of compression and temperature. Interestingly, the πc of (NHSCE)2 Langmuir monolayer depends on the strain rate of compression and temperature. A power law relation is used for analysis of the strain rate dependence of πc. On varying the temperature, initially we find an increase in πc with increase in temperature, a behavior known as alpha (α) flow. On further increase in temperature, we find decrease in πc, a behavior known as kappa (κ) flow. The α- flow is very unusual and has not been reported in literature for dimers. An analogy is drawn between the observed α- flow in (NHSCE)2 dimer and the yield strength anomaly reported for alloys.

Pattern Formation in Phase-Separated Langmuir and Langmuir Monolayer Films.

Mixed monolayer films comprising hydrogenated and fluorinated surfactants can undergo phase separation to produce interfaces with diverse structures at the micrometer and nanometer scales. This review discusses our progress over the past decade to probe the relationship that exists between the molecular structure of the surfactants that comprise the films and the overall patterns formed in the monolayers. We review two main classes of mixed perfluorocarbon-hydrocarbon surfactant systems, including fatty acids and a recently developed family of EDTA-based gemini surfactants. In addition to summarizing the state-of-the-art of this field, the key scientific questions and relationships that require further elucidation are discussed, along with directions for continuing research into this fascinating area of research.

Diffraction pattern of Bacillus subtilis CotY spore coat protein 2D crystals

Bacillus subtilis spore coat is a bacterial proteinaceous structure with amazing characteristics of self-organization, unique resiliency, toughness and flexibility in the same time. The spore coat represents a complex multilayered protein structure which is composed of over 80 coat proteins. Some of these proteins form two dimensional crystal structures who’s low resolution ternary structure as was determined by electron microscopy. However, there are no 3D structure of these proteins known, due to a problem of preparing 3D crystals which could be analyzed by synchrotron X-ray sources. In the present study, Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) was applied to investigate a diffraction pattern of CotY 2D crystals formed on Langmuir monolayer films. We observed two distinct diffraction rings and their position corresponds to a structure with the lattice spacing of 10.6 Å and 5.0 Å, respectively. Obtaining diffractions of 2D crystals pave the way to determination of 3D structure of coat proteins by using strong X-ray sources.

Structure and Elastic Properties of an Unsymmetrical Bi-Heterocyclic Azo Compound in the Langmuir Monolayer and Langmuir-Blodgett Film.

We study the structure and elastic properties of the bi-heterocyclic azo compound at the air–water interface through surface pressure (π)–area (A) isotherm recording followed by transferring them on hydrophilic and hydrophobic Si surfaces by the Langmuir–Blodgett (LB) deposition method. A substantial change in the area/molecule is observed as a function of subphase pH and temperature. Such parameters strongly influence intramolecular interactions within azo molecules and the interactions between azo molecules and water that manifested in higher surface activity at low temperature and high pH, which in turn modifies the elasticity of azo assembly at the air–water interface. A large pH-dependent hysteresis with negative change in entropy, indicating molecular rearrangements, is observed. Molecular assembly formed at the air–water interface is then transferred onto hydrophilic and hydrophobic Si surfaces at two different surface pressures (5 and 30 mN/m) by the LB technique. The structural analysis performed by X-ray reflectivity and atomic force microscopy techniques suggests that the LB films exhibit an abrupt layered structure on hydrophilic Si, whereas an overall rough film is formed on hydrophobic Si. The coverage and compactness of individual layers are found to increase with the deposition pressure (5 to 30 mN/m).

Ultrathin films of functionalised single-walled carbon nanotubes: a potential bio-sensing platform

ABSTRACT The Langmuir monolayer is a special class of lyotropic liquid crystalline system wherein phase transition essentially depends on surface density, temperature and ion-content in the aqueous medium. The variety of surface phases can be transferred onto devices by the Langmuir–Blodgett (LB) technique. The Langmuir monolayer of pristine single-walled carbon nanotubes (SWCNTs) exhibited gas and liquid-like phases. The LB film of SWCNTs shows target surface pressure dependent interesting morphologies. The methane gas sensing using parallel alignment of SWCNTs was found to be better than that of randomly oriented SWCNTs. The SWCNTs can be functionalised chemically to enhance the ease of film processability and affinity towards analytes. These are essential parameters for the development of a sensor. In this article, we present our work on Langmuir monolayer and LB films of octadecylamine functionalised SWCNTs (ODACNTs) and its sensing application towards bio-analytes, e.g. L-aspartic acid and bovine serum albumin. The sensing performance of LB film of ODACNTs was compared with that of spin-coated films of ODACNTs. The sensing performance of LB films of ODACNTs indicated a potential platform for bio-sensing application.

Meso-Substituted BODIPYs as supramolecular building blocks of ordered Langmuir–Blodgett films: structural and morphological characterization

Two crystalline meso-substituted BODIPYs were investigated as supramolecular building blocks of Langmuir–Blodgett (LB) thin films. These sorts of thin films are formed by the transfer of a Langmuir monolayer film of organized amphiphilic molecules onto a solid substrate. In the present contribution, we exploited the capacity of the featured BODIPYs to produce ordered supramolecular self-assemblies through hydrogen-bonding and π-stacking to pre-organize and to control their assembly as LB thin films. Electronic absorption and fluorescence emission of the meso-substituted BODIPYs in solution, LB films, and in solid state were studied. The morphology and structure of the LB films were examined by scanning electron microscopy and atomic force microscopy. The structural differences between both BODIPYs have no marked influence on the absorption and fluorescence emission properties in solution. In contrast, absorption properties in solid state (solid samples and LB thin films) depend on the structural nature of the dyes with the appearance of red-shifted bands, which could be an indicator of the presence of aggregates. The supramolecular information contained in the BODIPYs was reflected on the surface characteristics of the featured LB thin films. Both produced homogeneous and uniform films with the presence of some microcrystals, as the number of transferred monolayers increased. These results broaden the capacity of the Langmuir–Blodgett technique to produce ordered and self-assembled thin films of functional small organic molecules (such as BODIPYs) as components of different optoelectronic devices.

Application of the Langmuir Technique to Study the Response of C-dec-9-en-1-ylcalix[4]resorcinarene and C-undecylcalix[4]resorcinarene Ultra-thin Films' Interactions with Cd2+, Hg2+, Pb2+, and Cu2+ Cations Present in the Subphase

The calix[4]resorcinarene macrocycles are excellent oligomers for the design of amphiphilic derivatives; they can form self-assemblies and stable sensing networks. Owing to their favorable properties, they are the focus of many exploitations and studies ranging from biological controls to heavy metal ion sensing. In this perspective, two calix[4]resorcinarene derivatives, namely: C-dec-9-en-1-ylcalix[4]resorcinarene (ionophore I) and C-undecylcalix[4]resorcinarene (ionophore II) were used to form stable ultra-thin Langmuir monolayer films at the air/water interface; their interactions with different harmful metal cations (Cd2+, Pb2+, Hg2+, and Cu2+) were studied and highlighted via the pressure-area (Π-A) isotherms. The obtained results in the current investigation showed a dependence of both macrocycle interactions on the metal cation concentration in the subphase, confirming their complexation. In addition, the ionophore (I) exhibited high selectivity towards Pb2+ and Cu2+ cations, whereas the ionophore (II) showed tendency to bind with Cu2+ cations over others, approving the potential applicability of these macrocycles as ion selective chemical sensors.

Immiscible Anionic Gemini Surfactant-Perfluorinated Fatty Acid Langmuir Monolayer Films.

A new member of the N,N,N',N'-dialkyl-N,N'-diacetate ethylenediamine family of anionic gemini surfactants has been synthesized, and its miscibility with the model perfluorocarbon, perfluorotetradecanoic acid (PF), has been investigated in monolayer films at the air-water interface. Thermodynamics of mixing and the accompanying changes in the mixed film structure have been probed using a combination of compression isotherm measurements supported by Brewster angle microscope imaging and X-ray scattering measurements, and results have been compared with those collected for a previously studied, shorter tail chain variant of the surfactant. Thermodynamic measurements showed that the gemini surfactant and perfluorotetradecanoic acid were immiscible, with weak repulsive interactions, manifesting as small positive deviations from ideal mixing, observed between the two film components. Films were highly textured, with micrometer-scale, phase-separated domains readily detectable. Grazing incidence X-ray diffraction measurements showed that the gemini surfactant was disordered in the monolayers, whereas the perfluorocarbon formed discrete crystallites in the disordered matrix. Despite the small deviations from ideal mixing detected in the thermodynamic measurements, the X-ray measurements indicated that the presence of the gemini perturbs the PF crystal lattice from that of pure PF. Finally, X-ray reflectivity measurements showed that the addition of equimolar PF to the gemini monolayer induces a significant increase in the nominal head group thickness of the film, suggesting that interactions between the two surfactants can lead to structural rearrangements of gemini's head group near to the water surface.

Alignment of liquid crystals using Langmuir‒Blodgett films of unsymmetrical bent-core liquid crystals

ABSTRACTThe properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air–water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir‒Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.

Elucidation of the Origin of Thixotropic-Inducing Properties of Additive Amphiphiles and the Creation of a High-Performance Triamide Amphiphile.

The spontaneous growth of helical fibers of amphiphilic diamide derivatives containing hydrocarbons with asymmetric carbon centers in their constituent hydrocarbons was investigated. 12-Hydroxystearic acid and a gemini-type surfactant obtained by the bimolecular condensation of this compound with hexamethylenediamine both impart thixotropic ability to a solvent. Although this thixotropic behavior is based on the growth of hierarchical crystalline nanofibers in the solvents, the degree of fiber growth itself was not the origin of the thixotropy. In this study, it has adopted the methods of the Langmuir monolayer and Langmuir-Blodgett films as technique to selectively and individually evaluate the behavior of 12-hydroxyl stearyl and/or stearyl chains themselves. The ability to impart thixotropy to the solvent via fiber organization was related to the intermolecular hydrogen bonding between the added amphiphiles. Additionally, homogeneous right-handed helical fibers were formed in the spin-cast films of the diamide derivatives, and a positive Cotton effect was observed in their circular dichroism spectra. It is suggested that fibers that do not form helical arrangements cannot impart sufficient thixotropy to the solvent even when extensive fiber growth is achieved, and the structure-dependent development of chirality is the driving force. In addition, to further the development of highly functional thixotropic agents, a trefoil-like triamide derivative containing three chains was synthesized. By using this molecule, solvent gelation occurred at 78% as an addition to the diamide case, and a supramolecular assembly was formed in the corresponding two-dimensional film.

Brewster Angle Microscopy and Langmuir Monolayer Films: Construction of an Instrument and Basic Software Development for Visualization of Lipid Domains and Lipid Raft Formation

Brewster Angle Microscopy is a useful technique for the analysis of surface characteristics of films at the air‐water interface in a Langmuir monolayer trough due to its ability to obtain images while simultaneously collecting isothermal data. It provides an effective way of visualizing lipid domains, as well as lipid aggregation to form structures such as lipid rafts. The goal of this research was to construct a relatively low‐cost Brewster Angle Microscope (BAM) using LEGO™ Mindstorms, 3D printed components, a laser, a 10x microscope objective, and a CCD camera. This BAM was then used to obtain images of dipalmitoylphosphatidylcholine (DPPC) films and DPPC/Cholesterol films during a compression analysis. At the moment, we are working on programmatically quantifying the phase differences in lipid domains, as well as the surface density and thickness of films for analysis of lipid monolayers for drug delivery applications.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chitosan-fatty acid interaction mediated growth of Langmuir monolayer and Langmuir-Blodgett films

The interaction of chitosan with bio-membranes, which plays important role in deciding its use in biological applications, is realized by investigating the interaction of chitosan with stearic acid (fatty acid) in Langmuir monolayers (at air–water interface) and Langmuir-Blodgett (LB) films (after transferring it onto solid substrate). It is found from the pressure-area isotherms that the chitosan insertion causes an expansion of chitosan-fatty acid hybrid monolayers, which reduces the elasticity and make the film heterogeneous. It is likely that at low surface pressure chitosan is situated at the interface, interacting with stearic acid molecules via electrostatic and hydrophobic interactions whereas at high pressure chitosan mainly located at subsurface beneath stearic acid molecules. In the latter case the interaction is predominantly electrostatic yielding very small contribution to the surface pressure. The reduction of temperature of the subphase water allows more number of chitosan molecules to reach surface to increase the pressure/interaction. On the other hand, although pure chitosan is found difficult to relocate on the substrate from air-water interface due to its hydrophilic-like nature, it alongside stearic acid (amphiphilic molecules) can be transferred onto substrate using LB technique as evident from infrared spectra. Their out-of-plane and in-plane structures, as extracted from two complementary surface sensitive techniques- X-ray reflectivity and atomic force microscopy, are found strongly dependent on the chitosan mole fraction and the deposition pressure. These analysis of the film-structure will essentially allow one to model the system better and provide better insight into the interaction.

Mixing Behavior in Binary Anionic Gemini Surfactant-Perfluorinated Fatty Acid Langmuir Monolayers.

The miscibility and film structure of mixed Langmuir monolayer films composed of an anionic gemini N,N,N',N'-dialkyl-N,N'-diacetate ethylenediamine surfactant (Ace(12)-2-Ace(12)) with perfluorotetradecanoic acid (C13F27COOH; PF) have been investigated using a variety of thermodynamic and structural characterization methods. The two film components were found to be miscible in monolayers at the air-water interface over a range of compositions and at all but the lowest surface pressures, with attractive interactions occurring between the two components. While pure PF monolayers formed crystalline lattices with hexagonal symmetry and with the surfactant tails oriented normal to the underlying water subphase, the pure gemini surfactant formed amorphous films with little tendency to orient at the subphase. In mixed films with mole ratios of PF:Ace(12)-2-Ace(12) < 2.5, the miscibility of the two components resulted in a nearly complete loss of crystallinity of the PF, though films at higher mole fractions of PF showed some residual crystallinity, albeit with lattice structures that were significantly different from that of pure PF. Miscibility and film structure in this mixed system are discussed in comparison with other mixed gemini surfactant systems in the literature as well as binary mixtures of phospholipids or monomeric fatty acids with PF.

Self-Assembly Behaviors of a Well-Defined Amphiphilic Brush Polymer at the Air-Water Interface

Self-assembly characteristics of a well-defined brush polymer, poly(oxy(n-dodecyl-thiomethyl)ethylene) were in detail investigated at the air-water interface with surface–area isotherm, X-ray reflectivity, and infrared spectroscopy analyses. The brush polymer self-assembled at the air-water interface as a fully-extended chain via favorable lateral packing of the bristles in a fully extended conformation, forming highly ordered, oriented Langmuir monolayer. This well-ordered monolayer was produced via a five-regime structure formation with varying surface pressure. A Langmuir monolayer film with ≤1.92 nm thick was formed in the low surface pressure regime ≤18 mN/m and then converted to a highly dense, ordered monolayer with 3.65 nm thick in the high surface pressure regime ≥35 mN/m through monolayer-to-bilayer transition and bilayer-to-monolayer inversion. These Langmuir film formations and their ordering and orientation might be driven by the well-defined chemical architecture and the lateral orderings of the polymer backbones and the bristles in fully extended conformations.

Langmuir and Langmuir–Blodgett Films of Hybrid Amphiphiles with a Polyoxometalate Headgroup

A hybrid was at first synthesized by a postfunctionalization of an aminomethane trisalkoxo-functionalized Anderson-type polyoxometalate (POM) encapsulated by three tetrabutylammonium ions using a 3,5-bis(tetradecyloxy)benzoic acid by amidation. Then the three TBA(+) counter cations were programmatically replaced by protons (H(+)) following a molecule-to-amphiphile conversion. In this way one hybrid and three POM-containing hybrid amphiphiles (PCHAs) were acquired by adjusting the number (n) of TBA(+) ions and number (3 - n) of H(+) ions (n = 3, 2, 1, and 0). These compounds can be spread onto a water surface to form a Langmuir monolayer film at the air-water interface. Surface pressure-molecular area measurements exhibit the TBA(+) (H(+)) number playing an important role in the forming ability and stability of Langmuir monolayer films. Also, the Langmuir-Blodgett (LB) technique has been used to transfer the monolayer film onto solid supports to fabricate solid multilayer films. It was found that the PCHA with three H(+) ions had the best Langmuir film-forming ability and thus formed stable LB films with a two-dimensional ordered structure. Our findings are instructive in fabricating and using solid films of the amphiphiles with POM headgroups.

A New Mathematical Model to Measure the Parameters about the Formation of Binary Complexes in the Langmuir Monolayer Film and Relevant Experiment Research

A new mathematical model to measure the parameters about the formation of binary complexes in the Langmuir monolayer film was developed.Some important parameters such as the stability constant,the mean molecular areas of binary complexes and unpolymerized molecules,the proportion of molecules which formed complexes and so on could be got,through which a function about the relationship between the proportion of the amount of the molecules which had polymerized to the total amount of the molecules in the Langmuir monolayer,and the ratio of the amounts of two different components were derived for the first time.Dipalmitoylphosphatidylcholine(DPPC) and stearic acid(SA) were selected as materials to make Langmuir films to validate the new method.Following results were got: mean molecular areas of SA and DPPC are 24.0 2/molecule and 63.7 2/molecule respectively,the mean molecular area of dimers is 81.3 2/molecule,the stability constant at room temperature is 1.86 ×107 m2/mol,and the proportion of the molecules which have polymerized reaches its highest value-about 84.96% of the total molecules in the Langmuir monolayer when the proportion of the amount of SA is 49.73%.

Incorporation of Erythrosin B Within the Restricted Geometry of Langmuir Monolayer and Langmuir-Blodgett Films of Octadecylamine

This paper reports the monolayer characteristics of cationic octadecylamine (ODA) on both distilled water and aqueous Erythrosine B (EB) dye solution at the air-water interface. From the pressure-area isotherms at various pHs, EB anions in the subphase were found to interact with the insoluble monolayer of cationic octadecylamine (ODA). Adsorption kinetics shows that the amount of dye adsorbed depends on the concentration of the dye present in the subphase. It was observed that the adsorption process mainly occurred due to the electrostatic interaction between the cationic amino group of long chain amine and the anionic part of EB. The spectroscopic characteristics of the mixed LB films, solution, have been compared using UV-vis absorption and fluorescence spectroscopic data. These studies indicate the formation of aggregates in the thin films. Scanning electron microscopic study certainly confirms the presence of aggregates of EB dye in the (ODA-EB) mixed LB films.