Monolayers and multilayers of uranyl arachidate: in-plane structure of uranyl arachidate multilayers

The molecular in-plane structure of uranyl arachidate Langmuir-Blodgett (LB) films formed at different subphase pH values was analysed by means of X-ray grazing-incidence diffraction. For multilayers formed at low subphase pH a reorganisation of the arachidic acid film structure is confirmed. At appropriate subphase pH values, reorganisation of the film structure e.g. via the formation of three-dimensional crystallites, is prevented by the presence of the uranyl ions and by the subsequent introduction of conformational disorder (gauche defects) in the alkyl chains. The observation of a macroscopic flow-induced in-plane texture in these uranyl arachidate LB films has profound implications for the design of ordered, supramolecular structures by the Langmuir-Blodgett technique.     

冠醚和卟啉与花生酸混合单分子膜行为研究

本文将3'-正十五烷基苯并15-冠-5和六种无脂链难于直接成膜的四苯基卟啉与花生酸混合形成单分子膜。结果表明, 冠醚被嵌进而卟啉被挤出花生酸单分子层。卟啉-花生镉LB膜的可见吸收光谱指出卟啉分子成团聚集。扫描电镜观察了卟啉-花生酸镉混合LB膜的表面形貌, 在膜表面上无金涂层时直接测到了混合膜的相分离。     

Effect of water and air-water interface on the structural modification of Ni-arachidate Langmuir-Blodgett films

Nickel arachidate (NiA) Langmuir-Blodgett (LB) films have been deposited on hydrophilic Si(0 0 1) substrates by three (up-down-up) and five (up-down-up-down-up) strokes. During deposition, substrates were kept inside the water subphase for different times after each down stroke. Structural information of all the LB films have been obtained from X-ray reflectivity (XRR) studies. One and two symmetric monolayer (SML) was deposited on top of the asymmetric monolayer (AML) in three and five stokes respectively. All the preformed LB films were then used to go through the air-water interface with the same speed that was used at the time of film deposition. Structural information obtained from the XRR studies show that mainly the top layer density decreases after passing through the air-water interface but the layered structure remains the same. Information obtained from both the XRR and atomic force microscopy (AFM) studies suggest that molecules peeled from the top SML layer do not reincorporate with the LB film through tail-tail hydrophobic interaction. Our study shows that NiA LB film has better stability compared with cadmium arachidate LB film inside the water subphase without forming any out-of-plane molecular reorganization.     

Monolayers of mono- and bidisperse spherical polymer particles at the air/water interface and Langmuir-Blodgett layers on solid substrates

Monodisperse spherical polymer particles with anionic and cationic shells were studied for their monolayer formation and compression behaviour on an aqueous subphase as a function of pH and salt (KCl) concentration. In addition, monolayers of monodisperse and bidisperse mixtures of 434 and 214 nm sized anionic particles were studied for their morphology by scanning electron microscopy (SEM). The anionic particles were prepared by soap-free emulsion polymerization of styrene and acrylic acid, and the cationic particles from styrene and 2-acryloxyethyl trimethylammonium chloride. Independent of the chemical nature of the shell, the particles formed monolayers at high salt or acid concentration in the subphase. However, at neutral pH and if no salt was present in the subphase only a part of the spheres formed monolayers, while the residual particles disappeared into the subphase. The origin of this behaviour is discussed in terms of ionization and electrostatic shielding of the polar groups.Compressed monolayers of monodisperse particles consisted of randomly oriented domains of up to 20 particles with small holes in between, the holes not exceeding two particle diameters in size. Films of bidisperse mixtures were highly disordered. If small particles were present in excess, they formed a fairly disordered monolayer and the large particles were situated on top or below this layer. If the number ratio of both sorts of particles approached unity, the texture became disordered and bi- and multilayered aggregates were observed.     

Quartz Crystal Microbalance Study of Q-State PbS Particle Formation in Lead Arachidate Langmuir-BIodgett Films

The formation of Q-state PbS particle in lead arachidate (PbAr) Langmuir-Blodgett films has been monitored using the quartz crystal microbalance (QCM) measurement. The study showed that the mass uptake of PbAr films with different thicknesses on exposure to hydrogen sulfide was consistent with that expected for the quantitative conversion of Pb²⁺ in the films to PbS and the corresponding conversion of PbAr to arachidic acid. Mass uptake measurement on PbAr films extensively exposed to H₂S gas showed the arachidic acid molecules left after Q-state particle formation could be quantitatively converted to PbAr by immersing the film in a stirred aqueous solution containing lead ions. Subsequent reexposure of the film to H₂S increases the mole fraction of PbS in the film.     

Preparation, characterization, and application of polypropylene-clinoptilolite composites for the selective adsorption of lead from aqueous media

The miscibility, mechanical and morphological properties of mixed Langmuir and Langmuir-Blodgett monolayers prepared from the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and the perfluorinated fatty acid perfluorooctadecanoic acid have been studied as a function of film composition and subphase salinity. It was demonstrated here, for the first time, that the extent of surfactant miscibility in mixed phospholipid-perfluoroacid monolayers, and hence the resulting mechanical properties of the monolayer film, can be controlled by altering the concentration of sodium ions in the underlying subphase. Elevated Na(+) concentrations resulted in lower net attractive interactions between film components, likely through specific ion adsorption to the negatively-charged perfluoroacid, along with decreased film elasticities. These results differ significantly from conventional fatty-acid-carboxylate monolayer systems in which film cohesion is typically enhanced through adsorption of cations to surfactant headgroups. Atomic force microscope images of films deposited onto solid mica substrates revealed that the films deposited from pure water formed multimolecular aggregates of surfactant, which could be attributed to the highly cohesive nature of the films, but the use of salt in the subphase diminished aggregate formation and resulted in the production of homogeneous monolayer films.     

Surface-plasmon optical characterisation of asymmetric soap films

Stable water films covered by arachidic acid monolayers were prepared on vertically arranged glass/Ag/SiO₂-substrates, which were partially pulled out of a film balance trough. The thickness profiles were recorded by on-line-measurement, using the thickness dependence of the dispersion of surface plasmon polaritons. The surface plasmon imaging technique allows for a thickness resolution of 0.2 nm and a height resolution of ca. 20 μm. Variations of these profiles as a function of the lateral pressure of the horizontal arachidate layer on the film balance were observed. For the first time Raman studies were made on asymmetric soap films. The intensity ratio of the Δη_a = 2800 cm⁻¹ to the Δη_s = 2850 cm⁻¹ line in the CH-stretching vibration range shows a dependence on the lateral pressure in the monolayer.     

MONOLAYER STUDIES OF 5-(4-CARBOXYPHENYL)-10,15,20-TRITOLYL-PORPHYRIN–I. OPTICAL STUDIES OF FILMS AT THE AIR-WATER INTERFACE and OF FILMS TRANSFERRED ONTO SOLID SUBSTRATES†

Abstract— The title compound forms well-behaved monomolecular films at the air-water interface. The surface pressure-molecular area isotherms change with the pH of the subphase in a manner which suggests that the carboxylic acid group acts as the hydrophylic portion of the molecule with a pK_a of –7.3. In compressed monolayers the porphyrin ring appears to be oriented so that the plane of the ring is perpendicular to the surface. Spectroscopic studies of single monolayer films transferred to quartz slides using the Langmuir-Blodgett technique indicate that three distinct species are present in the films, with the amount of each phase depending on the pH of the subphase. One species, present at low pH, is assigned as a monomer on the basis of its optical and fluorescence spectra and its fluorescence lifetime. At low pH this monomer species co-exists with another non-fluorescent aggregated species. For films formed on subphases with pH > 7.3, these two species are converted to a single, weakly fluorescent species which exhibits an unusual absorption spectrum. We postulate that this third species is a constrained aggregate but rule out the possibility of a face-to-face dimer on spectroscopic grounds. For films at the air-water interface specular reflection, indicative of a smooth, highly absorbant film, is observed from monolayers of the title compound. Visual examination of this phenomenon proved to be very useful in assessing the completeness of spreading and the collapse point. Under certain conditions a distinct macroscopic structure is observed in the monolayer film. This structure is interpreted as evidence for the presence of two or more two-dimensional crystalline phases. Support for this view comes from previous measurements of specular reflection on single crystals of tetraphenylporphyrin. There is no indication that variations in the macroscopic structure of the films have any significant effect on the microscopic properties such as the surface pressure-area isotherms.     

Langmuir–Blodgett Films of Fatty Acid Salts of Bi- and Trivalent Metals: Y, Ba, and Cu Stearates

Dependences of the composition and properties of the monolayers and Langmuir–Blodgett films of yttrium, barium, and copper stearates on the conditions of their formation were studied by FTIR spectroscopy, X-ray photoelectron spectroscopy, and quartz crystal microbalance technique. The identity of film compositions on the surfaces of liquid and solid substrates was established. It was shown that, in the case of copper and yttrium, the Langmuir–Blodgett films are formed from corresponding basic salts of stearic acid at high subphase pH values. The conditions of the preparation of high-quality Langmuir–Blodgett films from yttrium, barium, and copper stearates are determined.     

Equilibrium structure and dynamics of (2R, 3R)-(+)-bis(decyloxy)succinic acid at the air-water interface

A twin-tailed, twin-chiral fatty acid, (2R,3R)-(+)-bis(decyloxy)succinic acid was synthesized and its two dimensional behavior at the air-water interface was examined. The pH of the subphase had a profound effect on the monolayer formation. On acidic subphase, stable monolayers with increased area per molecule due to hydrogen bonding and bilayers at collapse pressures were observed. Highly compressible films were formed at 40 degrees C, while stable monolayers with increased area were observed at sub-room temperatures. Langmuir monolayers formed on subphases containing 1 mM ZnCl2 and CaCl2 revealed two dimensional metal complex formation with Zn2+ forming a chelate-type complex, while Ca2+ formed an ionic-type complex. Monolayers transferred from the condensed phase onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. Compression induced crystallites in 2D from monolayers and vesicle-like supramolecular structures from multilayers were the noted LB film characteristics, adopting optical imaging and electron microscopy. The interfacial monolayer structure studied through molecular dynamics simulation revealed the order and packing at a molecular level; monolayers adsorbed at various simulated specific areas of the molecule corroborated the (pi-A) isotherm and the formation of a hexagonal lattice at the air-water interface.     

硬脂酸单分子膜上电沉积Ag膜的研究

通过电沉积方法,以气/液界面上形成的硬脂酸单分子膜为模板诱导沉积金属银膜.考察了镀液pH值、单分子膜表面压及沉积电位对银膜形貌及结构的影响.实验发现,酸性镀液的气/液界面上形成的单分子膜不能诱导沉积银,而在中性和碱性镀液的气/液界面上可以诱导银膜的生长.当单分子膜处于液态或固态时,气/液界面有银膜形成;液态单分子膜上的银膜生长速度较快,且银膜的结构一致.随着电极电位的升高,银膜沉积的速度加快,呈环状向外生长的圆形银膜逐渐变得不规则.将不同实验条件下的银膜转移出来,采用扫描电镜(SEM)、透射电镜(TEM)对银膜的结构与形貌进行了表征.研究表明,银首先在单分子膜上异相成核,由八面体构型逐渐发展成星型,最终在气/液界面形成具有松枝状微观结构的光亮银膜.     

INDUSTRIAL NEWS

Interactions between monolayers of trilaurylamine (TLA) and various water-soluble corrosion, hydrate and scale inhibitors, as well as acetic acid and FeCl₂, have been studied by means of the Langmuir technique, The water-soluble compounds were present in the subphase before TLA was spread. Their influence on the monolayer properties were measured by means of surface pressure-area ( k-A) isotherms and constant surface pressure-area relaxation measurements. All the added water soluble species gave rise to monolayer expansion. The monolayer expansion observed for TLA at pH 1, increased when FeCl₂ was added to the subphase at the same pH. Polyethyleneglycols with molecular weight higher than 200 destabilized totally the TLA-monolayer, probably due to bending and folding into multilayers. Monolayer expansion and film instability increased with increased acetic acid concentrations. The destabilization mechanism in this case was most likely due to a combination of nucleation and dissolution of film components into the subphase. The corrosion inhibitor Dyno KI 384 had a higher surface activity than TLA. Hence the monolayer     

Metal ion-induced H-aggregation of a water-soluble anionic dye Congo red (CR) in Langmuir–Blodgett (LB) film

Present communication reports the preparation of Langmuir monolayer of water-soluble anionic dye Congo red (CR) by allowing it to adsorb from the aqueous subphase onto the preformed Langmuir monolayer of anionic stearic acid using divalent metal cations Mg²⁺ as mediator. Isotherm and compressibility studies of SA-Mg-CR hybrid monolayer gave valuable information about the molecular organisation in the Langmuir monolayer. Absorption spectroscopic studies revealed the formation of H-aggregates in the hybrid Langmuir–Blodgett (LB) films fabricated at lower salt concentration in the subphase. Atomic Force Microscopic image gave visual evidence of distinct nanocrystalline domains in the LB monolayer film.     

Mixed monolayers of alkylated azacrown ethers and palmitic acid at the air-water surface

The Langmuir films of two alkylated azacrown ethers at the air-water surface were characterized using surface pressure-area isotherms, ellipsometry, Brewster angle microscopy, and constant-area surface pressure relaxation. The azacrown ether molecules aggregate in the monolayer, which significantly stabilizes the film against dissolution. Mixed azacrown ether-palmitic acid monolayers were also characterized; results suggest that at high compression the two molecules interact repulsively. The influence of Cu(II) ions present in the aqueous subphase on the single components and mixed monolayer characteristics was also studied.     

Transition from homogeneous Langmuir-Blodgett monolayers to striped bilayers driven by a wetting instability in octadecylsiloxane monolayers

We show that two dips of an oxidized silicon substrate through a prepolymerized n-octadecylsiloxane monolayer at an air-water interface in a rapid succession produces periodic, linear striped patterns in film morphology extending over macroscopic area of the substrate surface. Langmuir monolayers of n-octadecyltrimethoxysilane were prepared at the surface of an acidic subphase (pH 2) maintained at room temperature (22 +/- 2 degrees C) under relative humidities of 50-70%. The substrate was first withdrawn at a high dipping rate from the quiescent aqueous subphase (upstroke) maintained at several surface pressures corresponding to a condensed monolayer state and lowered soon after at the same rate into the monolayer covered subphase (downstroke). The film structure and morphology were characterized using a combination of optical microscopy, imaging ellipsometry, and Fourier transform infrared spectroscopy. An extended striped pattern, perpendicular to the pushing direction of the second stroke, resulted for all surface pressures when the dipping rate exceeded a threshold value of 40 mm min(-1). Below this threshold value, uniform deposition characterizing formation of a bimolecular film was obtained. Under conditions that favored striped deposition during the downstroke through the monolayer-covered interface, we observed a periodic auto-oscillatory behavior of the meniscus. The stripes appear to be formed by a highly correlated reorganization and/or exchange of the first monolayer, mediated by the Langmuir monolayer at the air-water interface. This mechanism appears distinctly different from nanometer scale stripes observed recently in single transfers of phospholipid monolayers maintained near a phase boundary. The stripes further exhibit wettability patterns useful for spatially selective functionalization, as demonstrated by directed adsorptions of an organic dye (fluorescein) and an oil (hexadecane).     

液晶聚合物的单层与Langmuir-Blodgett膜

系统研究了手性液晶聚硅氧烷和光致变色液晶聚硅氧烷两个毓的侧链液晶聚合物在空气/水界面的单层行为和Langmuir-Blodgett(LB)膜沉积特性,对LB膜结构与存在的聚集现象进行了系统的表征,并初步探讨了LB膜中液晶聚合物表现的功能性。     

一种新的共轭桥联双二茂铁衍生物的单层LB膜及其电催化效应

合成并表征了一种新的非两亲性共轭桥联双二茂铁衍生物，该化合物在空气／水界面上易形成较稳定的单分子膜，与花生酸形成的混合膜易组装成ＬＢ膜，紫外－可见吸收光谱表明：ＬＢ上膜分子中发生了聚集，扫描电镜观察了混合单层ＬＢ膜的表面形貌及膜的相分离。循环伏安研究表明：混合单层ＬＢ膜修饰电极对Ｆｅ（ＣＮ）／Ｆｅ（ＣＮ）离子对的电化学反应具有良好的电催化效应，对抗坏血酸电化学氧化具有明显的促进作用。     

Langmuir–Blodgett Monolayers and Films of Alkylated Tetraazacrowns Containing Metal Ions and Nanoparticles

The behavior of individual 1,7-dicetyltetraaza-12-crown-4 and its mixture with 1,4,7,10-tetracetyltetraaza-12-crown-4 in the Langmuir monolayers at the subphases containing Cu(II) ions or colloidal gold particles is studied. Based on the compression isotherms, the complexing ability of these amphiphilic cyclenes in a monolayer at the surface of aqueous dilute solutions of copper salt is established. It was shown that the fraction of complexes in a monolayer is proportional to the copper ion concentration in the subphase. Using surface balance, atomic force microscopy, and electron microscopy methods, it was revealed that the monolayer of dicetylcyclene at the surface of gold hydrosol binds nanoparticles from the subphase; the number of particles bound by the monolayer is proportional to their content in the hydrosol. The Langmuir–Blodgett films (LBF) of dicetylcyclene are prepared; their ability to bind copper ions from solution was disclosed by quartz crystal microbalance. The LBFs of dicetylcyclene containing gold nanoparticles in each layer are assembled.     

Effect of Metal Ions on the Formation and Properties of Monolayers and Nanosized Langmuir-Blodgett Films Based on Diphilic Aminomethylated Calix[4]resorcinarenes

The behavior of the monolayers of three diphilic aminomethylated calix[4]resorcinarene (CRA) derivatives on the surface of a pure aqueous subphase and subphase containing copper(II), nickel(II), europium(III), terbium(III), and lanthanum(III) ions was investigated. The monolayer transfer to the quartz and single-crystal silicon substrates was accomplished by the Langmuir-Blodgett (LB) technique. The films were studied by ellipsometry and mass-spectrometry. Metal ions were found to exert effect on the limit area per one CRA molecule in the monolayer, on the surface collapse pressure and transfer coefficient of monolayer, and on the thickness and refractive index of the CRA-based LB films.     

Mechanistic insight into domain formation and growth in a phase-separated Langmuir-Blodgett monolayer

The mechanism of the formation and growth of phase-separated domains in mixed arachidic acid (C19H39COOH) (AA) and perfluorotetradecanoic acid (C13F27COOH) (PA) monolayer films was investigated through a combination of surface pressure-area isotherm measurements and atomic force microscope (AFM) imaging. In the mixed AA-PA monolayer system, distinct discontinuous domains consisting primarily of AA form spontaneously in a surrounding continuous matrix enriched in PA. By varying the monolayer deposition conditions, including temperature, surface pressure, and the mechanical agitation of sample solutions, it was determined that phase-separated nuclei are formed initially in the bulk sample solution and further growth of domains proceeds on the subphase surface via an Ostwald ripening process involving the diffusion of AA from the matrix to the discontinuous domains. In addition, selective dissolution of the arachidic acid followed by in situ AFM imaging has allowed the visualization of the fusion of AA to the phase-separated domains and has highlighted some unusual pattern formation that occurs at low subphase temperatures.