Formation Of Langmuir Monolayers Research Articles

Evolution of Nickel-Stearate Langmuir Monolayers and the Synthesized NiOx Ultra-Thin Films with pH

Abstract In this work Ni-Stearate (Ni-St) Langmuir-Blodgett (LB) films are oxidized to synthesize uniform ultra-thin films of Nickel oxide (NiOx). Pressure-Area (π-A) isotherms and oscillatory barrier method are used to examine the Ni-St Langmuir monolayers. Increase in the sub-phase pH during Langmuir monolayer formation results in higher compaction and elasticity for the solid phase. NiOx thin films synthesized with 15 layers of Ni-St at pH 7.9 are continuous, uniform and have a band gap of 4.04 eV. Changing the value of pH results in non-continuous films. XRD of the 200 layer films identifies the final phase formation after sintering as Ni2O3.

Preparation and Characterization of a Novel Organic Semiconductor Indacenedithiophene Derivative and the Corresponding Langmuir-Blodgett Thin Films.

The synthesis of a novel indacenedithiophene derivative (IDT-DPA) is described, which exhibits semiconducting behavior. Its properties were measured by means of UV-visible and fluorescence spectroscopies using toluene as solvent. An extinction molar coefficient of 2.05×10⁴ M-1 cm-1 and a Stokes shift of 50 nm were obtained. A theoretical study was performed using the density functional theory, from which HOMO-LUMO band gap of 1.711 eV was calculated. IDT-DPA was deposited on the water-air interface to form Langmuir monolayers. π-A curves and hysteresis were measured showing reversibility behavior. The monolayers were transferred to glass substrates as Langmuir-Blodgett thin films. Their morphological properties were characterized by using scanning electron and atomic force microscopy, which showed that the films tend to form clusters with a homogeneous distribution. Absorption and emission spectra of the films were measured, from which the optical band gap and Stocks shift were derived. Based on the electronic properties and light emission spectra of IDT-DPA, this compound can be proposed for the applications in organic lightemitting diodes and other organic semiconductor devices.

Close-Packed Langmuir Monolayers of Saccharide-Based Carbon Dots at the Air-Subphase Interface.

Carbon dots (CDs) are zero-dimensional carbon-based spherical nanoparticles with diameters less than 10 nm. Here, we report for the first time CDs forming stable Langmuir monolayers at the air-subphase interface. Langmuir monolayers are of great interest both fundamentally to study the interactions at the interfaces and for many applications such as the development of sensors. However, CDs usually do not form Langmuir monolayers because of their highly hydrophilic nature. In this study, amphiphilic CDs were prepared through hydrothermal carbonization using saccharides as the precursors. The surface chemistry behavior and optical properties of CDs at the air-subphase interface were studied. CDs derived from saccharides consistently formed stable Langmuir monolayers which show all essential phases, namely, gas, liquid-expanded, liquid-condensed, and solid phases. The compression-decompression cycle method showed minimum hysteresis (4.3%), confirming theretaining capacity of the CDs as a monolayer. Limiting CD areas from surface pressure-area isotherm at the air-subphase interface were used to calculate the average diameter of the CDs at the air-subphase interface. UV/vis absorption spectra of CDs dispersed in water and in Langmuir monolayers had the same bands in the UV region. The intensity of the UV/vis absorption increases with increasing surface pressure at the air-subphase interface. Interestingly, photoluminescence (PL) of the Langmuir monolayer of CDs was excitation-independent, whereas the same CDs had excitation-dependent PL when dispersed in water.

Structural characteristics of lysozyme Langmuir layers grown on a liquid surface from an oligomeric mixture formed during the early stages of lysozyme crystallization

An approach for forming Langmuir monolayers of proteins is described, with lysozyme serving as an example. The essence of this approach is the deposition of a lysozyme solution containing a precipitant, KCl, onto the water surface in a Langmuir trough. The results of small-angle X-ray scattering indicate that the precipitant in the protein solution causes a significant fraction (>10%) of the protein molecules to assemble into dimers and octamers. Studying the formation of these monolayers by grazing-incidence X-ray standing waves (or X-ray standing waves under total external reflection conditions) showed that the thickness of the resulting protein layer was twice the diameter of an individual lysozyme molecule and matched the diameter of the octamer. Thin layers of precipitant ions (K and Cl) formed directly under the protein monolayer. Our results indicate that adding precipitant to the solution caused the formation of octamers with a retained structure that participated in Langmuir monolayer formation when the solution was applied to the water-subphase surface. Thus, the precipitant ions interacted with the protein monolayer. The proposed approach could facilitate the formation of ordered protein films in hybrid system design and in developing transition methods for nature-like technologies.

A comparative study on the effect of structural variations of co-solvent on the Tetronic® micelles with widely different hydrophobicity

Here we report, a comparative study on the micellization and phase behavior of two commercially available ethylene oxide – propylene oxide (EO-PO) octablock copolymers, Tetronics® 1304 and 1307 (hereafter written as T1304 and T1307), in the presence of 2,2,2‑trifluoroethanol (TFE) and ethanol (EtOH) using cloud point (CP), dynamic light scattering (DLS), high sensitivity differential scanning calorimetry (HSDSC), relative viscosity and Langmuir film balance. These copolymers fabricated with almost the same PO block length vary in their EO chain lengths and hence display different characteristics. T1304 shows a more hydrophobic character and forms micelles at ambient temperature while T1307, due to longer EO chain length, exhibits high hydrophilicity and faces difficulty in forming micelles which results into high polydispersity in the aqueous system. In the presence of co-solvents TFE and EtOH, however a more interesting behavior is noted. T1304, as evident from DLS and viscosity measurements, displays micellar growth in the presence of TFE, while the presence of EtOH induces micellar breakdown. Though, in case of T1307, presence of TFE improves micellization and a single micellar peak becomes evident in the DLS stacks, no micellar growth can be noticed both through DLS and relative viscosity, which is possibly due to its highly hydrophilic character. Likewise, presence of TFE depresses the CMT in both the copolymers while EtOH increases it. A similar trend is also justified by π-A isotherms form Langmuir monolayers.

Crucial role of the hydroxyl group orientation in Langmuir monolayers organization–The case of 7-hydroxycholesterol epimers

Oxysterols, which are products of cholesterol oxidation, are important biological molecules. For our investigations we have selected two epimers: 7α-hydroxycholesterol (7α-OH) and 7 β-hydroxycholesterol (7β-OH). Both molecules have been found to be capable of stable Langmuir monolayer formation, however, the characteristic of their monolayers were quite different. Contrary to 7β -OH, which isotherm devoid any transition, the π/A dependence for 7α-OH displayed a broad plateau. Temperature strongly affected this plateau transition – the lower the temperature, the higher the surface pressure of the transition. Such an inverse temperature dependence is uncommon for classical film-forming molecules. Film thickness results excluded multilayers as the probable cause for this plateau. Based on theoretical calculations it was possible to infer that the plateau can be attributed to the change of orientation upon film compression, from being anchored mainly with both polar groups in the pre-plateau region to that with one polar group being detached from the water surface in the post-plateau region. Differences in surface behavior of both diastereoisomers have been explained as being due to orientation of OH groups in their molecules; i.e. for 7β-OH both hydroxyl groups (at C3 and C7) are situated on the same side of the rings A and B, while for 7α-OH – on different sides, which induces the lifting off of one OH group from the water surface.

The Formation of arachidic acid Langmuir monolayers on the NiCl2 solution

The article describes the features of the formation of arachidic acid Langmuir monolayers on a water or NiCl2 solution subphase surface. Monolayers structure was investigated by analyzing the compression isotherms and Brewster angle microscopy methods. Films on the solid substrate (glass plates) were investigated by atomic force microscopy method for morphology. Film structure was studied as a function of the concentration of salt in subphase and exposure time. It is shown that the structure of films obtained by using NiCl2solution as subphase is not homogeneous and we can see some grains in thin films.

A studying of subphase temperature and dissolved ascorbic acid concentration influence on the process of Langmuir monolayer formation

Some of the prosperities of ascorbic acid (AscA) as a subphase, temperature and concentration were investigated in the Langmuir technique. We studied the forms of ascorbic acid (L- & D-AscA) actions as a subphase on monolayer formation in different concentration with different temperature in the Langmuir technique as a model of cell membranes under fixed pressure. In this study we have been noticed that there are different effects of ascorbic acid (L- & D-AscA) forms as a subphase, temperature and concentration. These results have many advantages include the possible fine control over the composition, circumstances and packing of the membrane being mimicked.

Synthesis of amphiphilic V-type silica nanogels and study of their self-assembling at the air–water interface

The methods for the synthesis of silica nanogels and a modifying agent, as well as related amphiphilic V-type silica nanogels are presented. Self-assembly of the synthesized amphi philic nanogels during the formation of Langmuir monolayers at the air–water interface is considered. Aggregate structures were revealed to form during ordering of the silica V-type nanogels at the air–water interface after collapse of the Langmuir monolayer. For the low-molecular-weight fraction of the silica nanogels, the aggregates do not completely decompose upon the expansion of the Langmuir layer since are formed by mutually penetrating macromolecules. For the highmolecular- weight fraction, they are reversibly formed and decompose in consecutive compression– expansion cycles, which is characteristic of Langmuir layers of nanoparticles.

Hydrophobic ionic liquids at liquid and solid interfaces

Abstract The aim of the present work was to contribute for a deeper understanding of the intermolecular interactions present in ionic liquid (IL) tribofilms through the comparative study of the ILs behavior at water and at silica surfaces. Three hydrophobic ILs were investigated at the air/water interface (Langmuir trough) and at the water/silica interface (adsorption, friction and wear). The same experiments were repeated with aqueous solutions of ILs containing the anionic surfactant sodium n-hexadecylsulphate (SHS). The main conclusion was that ILs and IL + SHS solutions able to form Langmuir monolayers are those which adsorb more strongly on the silica surface and which provide better protection to surface wear.

Effect of chemical structure of fluorinated polyhedral oligomeric silsesquioxanes on formation of Langmuir monolayers and Langmuir-Blodgett films

Fluorinated polyhedral oligomeric silsesquioxanes (F-POSS) due to their nanoscale hybrid structure coupled with hydrophobic substituted chains have drawn significant attention as highly hydrophobic and oleophobic materials. That is why the surface properties of such compounds at the molecular level should be analyzed in details. Therefore we studied four different fluorinated closed cage polyhedral oligomeric silsesquioxanes (POSS) using Langmuir and Langmuir-Blodgett (LB) techniques. The monolayer behavior was investigated by measurements of the surface pressure-area (π-A) isotherm and morphology of the films was visualized using Brewster angle microscopy (BAM). The rheological behavior was investigated using interfacial shear rheometer (ISR). The unusual properties of these silsesquioxanes result from their unsymmetrical structure. The hydrophobic character of their fluorinated substituents, combined with the hydrophilicity of the trimethoxysilane moieties lead to specific monolayer properties. The compounds were found to form stable monolayers at the air/water (A/W) interface however the surface activity of POSS derivatives decreases with increasing content of fluorinated moieties in the POSS structure. The monolayers of the studied POSS compounds were also successfully transferred onto the solid substrates as Y-type Langmuir-Blodgett films. The wettability and the structure of the LB film were investigated by measuring the static water contact angle on the glass surface. The presence of fluorinated moieties in the structure of POSS molecules governs the enhanced hydrophobic properties of solid substrate modified by the LB film.

Влияние состава субфазы и внешних условий на формирование и свойства ленгмюровского монослоя

Влияние состава субфазы и внешних условий на формирование и свойства ленгмюровского монослоя

Molecular simulation of langmuir monolayer formation by Gd(III) stearate complexes

Clusters simulating the formation of Gd(III) stearate complex monolayers on the surface of an aqueous phase are studied by means of molecular mechanics. From a comparison of the calculated and experimental data, it concluded that Langmuir monolayers are produced by Gd(III) aqua complexes with one and two stearate anions.

Stable blue phase polymeric Langmuir-Schaefer films based on unsymmetrical hydroxyalkadiynyl N-arylcarbamate derivatives

Unsymmetrical diynes containing N-arylcarbamate groups in the hydrophobic part and hydroxymethylene groups in the hydrophilic part of the molecules were synthesized and studied. The Langmuir monolayer formation process was followed by Brewster angle microscopy (BAM). The Langmuir-Schaefer monolayer films, transferred on solid substrates (quartz or Si), were investigated by absorption spectroscopy and atomic force microscopy (AFM). Four substances had 2 methylene groups in the hydrophilic part of the molecule (n) and 4 or 5 of these groups in the hydrophobic part (m). At the same time the aryl substituent had a hydrogen atom or a MeO group in the p-position of the benzene ring. After 20min of UV irradiation the initially colorless monomeric films of all four compounds turned into stable blue phase polymeric films. The blue phase is unusual for alcoholic diacetylene derivatives. The BAM and AFM measurements demonstrated higher homogeneity of the films with a MeO group in the aryl substituent in comparison to the molecules with a hydrogen atom. The reasons for these different structural organizations as well as potential applications of stable blue phase polydiacetylene thin films are discussed.

Organization of polythiophenes at ultrathin films mixed with stearic acid investigated with polarization-modulation infrared reflection–absorption spectroscopy

In this present work, the polymers poly(3-alkylthiophene)s, regioregular poly(3-butylthiophene), poly(3-hexylthiophene) and poly(3-octylthiophene) were spread at the air-water interface to form Langmuir monolayers. They formed stable films by mixing them with Stearic Acid (SA), as confirmed with surface pressure-area isotherms and polarization-modulation infrared reflection–absorption spectroscopy (PM-IRRAS). The floating monolayers were transferred from the liquid interface to solid supports by using the Langmuir-Blodgett (LB) and Langmuir-Schaeffer (LS) techniques, and characterized with PM-IRRAS. Surface pressure-area isotherms showed that SA monolayers are expanded upon polymer incorporation altering the rheological properties of the monolayer since the monolayer became less elastic at higher pressures and presented first-order transitions at lower pressures. PM-IRRAS showed that the organization of the films is affected at the molecular level depending on the chemical structure of the polymer chosen. Among the polymers analysed, the poly(3-butylthiophene) shows a more irregular conformational behaviour depending on the amount of stearic acid. The conformation of the films when transferred to solid support changes and is dependent on the type of deposition (LB or LS). The importance of this paper relies on the fact that SA can be employed to help the formation of stable floating monolayers of these polythiophenes at the air-water interface, and the successful transfer to solid supports may provide nanostructured films with a high control of their molecular properties, which may enable a molecular architecture to be applied as electronic devices of interest.

Langmuir and Langmuir-Blodgett films of di-ureasil hybrid compounds containing phosphotungstic acid

The search for new molecular architectures to improve the efficiency of sensors and optoelectronic devices is fundamental to enhance the effectiveness of nanostructured materials. In this present work, a di-ureasil hybrid compound (DUPTS) was spread at the air-water interface in order to form Langmuir monolayers. Phosphotungstic acid, H3PW12O40, PWA inserted in the aqueous subphase stabilized the formation of DUPTS as a stable Langmuir film, as showed with surface pressure and surface potential-area isotherms, rheological measurements, polarization modulation reflection-absorption spectroscopy, and Brewster angle microscopy. The monolayers were transferred to solid supports as Langmuir-Blodgett films and presented different patterns of heterogeneity as observed with atomic force microscopy, with the morphology dependent on the presence of PWA and on the kind of solid support surface.

ISOTHERM AND X-RAY MEASUREMENTS OF A LANGMUIR MONOLAYER OF A NON-POLAR HYDROCARBON CHAIN MOLECULE

Traditionally Langmuir monolayers and lipids bilayers (including cell membranes) on water interfaces are made of amphiphilic molecules with both polar hydrophilic and non-polar hydrophobic parts. It has been discovered that non-polar hydrocarbon chain molecules without the polar hydrophilic part, can also form Langmuir monolayers on water when the chain molecule has more than 30 carbon atoms. Here we report the surface pressure vs. area isotherm measurements of a H(CH2)36H film on water, which show the film’s maximum compression modulus (greatest resistance to lateral compression) at about 19 Å2/molecule, independent of the compression speed, like the Langmuir monolayers of long chain saturated fatty acids do. The cross-section area of the hydrocarbon chain is about 19 Å2. Our measurements confirm the formation of a Langmuir monolayer by H(CH2)36H, a non-polar hydrocarbon chain molecule. X-ray measurements reveal structural information of the monolayer.

Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers.

The surface morphology and organization of poly(ionic liquid)s (PILs), poly[1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir-Blodgett (LB) monolayers at the air-water and air-solid interfaces is demonstrated. The hydrophobic bis(trifluoromethylsulfonyl)imide (Tf2N-) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films.

Synthesis and properties of water-soluble silica nanoparticles

Methods for synthesis and optimum conditions of the formation of stable water-soluble silica nanoparticles are presented. The silica nanoparticles were synthesized by the hydrolytic polycondensation of tetraethoxysilane using two methods: under alkaline conditions (Stober´s method) or in an acetic acid medium followed by the modification by grafting triethylene oxide moieties on the particle surface. The structure of the modified silica nanoparticles was confirmed by the data of IR and NMR spectroscopy. Polydispersity was evaluated by gel permeation chromatography and dynamic light scattering. The formation and stability of Langmuir monolayers of the silica nanoparticles modified by triethylene oxide moieties were studied.

Saponin Interactions with Model Membrane Systems – Langmuir Monolayer Studies, Hemolysis and Formation of ISCOMs

Saponins are used in medicine due to their pharmacological and immunological effects. To better understand interactions of saponins with model membranes and natural membranes of, for example, erythrocytes, Langmuir film balance experiments are well established. For most saponins, a strong interaction with cholesterol was demonstrated in dependence of both the aglycone part and the sugar moieties and is suggested to be correlated with a strong hemolytic activity, high toxicity, and high surface activity, as was demonstrated for the steroid saponin digitonin. In general, changes in the sugar chain or in substituents of the aglycone result in a modification of the saponin properties. A promising saponin with regard to fairly low hemolytic activity and high adjuvant effect is α-tomatine, which still shows a high affinity for cholesterol. An interaction with cholesterol and lipids has also been proven for the Quillaja saponin from the bark of Quillaja saponaria Molina. This triterpene saponin was approved in marketed vaccines as an adjuvant due to the formation of immunostimulating complexes. Immunostimulating complexes consist of a Quillaja saponin, cholesterol, phospholipids, and a corresponding antigen. Recently, another saponin from Quillaja brasiliensis was successfully tested in immunostimulating complexes, too. Based on the results of interaction studies, the formation of drug delivery systems such as immunostimulating complexes or similar self-assembled colloids is postulated for a variety of saponins.