Blodgett Layers Research Articles

Frictional electrification between flat surfaces of polymers and of Langmuir–Blodgett layers

A friction apparatus was constructed for measuring the frictional electrification due to reciprocating friction between flat materials such as polymer films or LB layers deposited on flat substrates. The apparatus is equipped with four electrodes by which it is possible to measure generation and decay processes of charges on both surfaces simultaneously. The frictional electrification of LB layers is useful for constructing a frictional electrification series of atomic groups that elucidates the effect of surface conditions of molecular aggregates like polymers and that is useful for designing a new type of antistatic material.

Visualization of Chemical and Physical Properties of Calcium-Induced Domains in DPPC/DPPS Langmuir−Blodgett Layers

In this study, we explored the calcium-induced formation of phosphatidylserine-enriched lipid domains in Langmuir−Blodgett (LB) monolayers composed of the binary mixture of the two saturated lipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS) in a molar ratio of 4:1 by means of surface analysis tools. We employed fluorescence microscopy in conjunction with pressure−area isotherms, time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging, scanning electron microscopy (SEM), and lateral force microscopy to visualize and analyze lipid domains by their chemical and physical properties. TOF-SIMS and SEM images of DPPC/DPPS LB monolayers transferred onto gold surfaces clearly reveal that small amounts of calcium ions in the aqueous phase are sufficient to trigger the formation of circular DPPS-enriched domains, but domain formation is abolished in the presence of ethylene glycol-bis(β-aminoethyl) ether-N,N,N‘,N‘-tetraacetic acid (EGTA). Latera...

Subresolution axial distance measurements in far-field fluorescence microscopy with precision of 1 nanometer

Fluorescent objects closer than the diffraction resolution limit can be distinguished in far-field microscopy provided they feature different emission spectra. Utilizing the superior axial resolution of 4Pi-confocal microscopy of 100–150 nm, we investigate the precision with which fluorescence objects with subdiffraction axial distance can be measured in the far field. At a wavelength of 820 nm distances on the order of 60 nm between beads and a monomolecular Langmuir–Blodgett layer were determined with a precision of 1.2 nm within 3.2 s. The reduced spatial extent of the 4Pi-confocal point-spread-function improves the precision of colocalization measurements in double stained specimens and opens up the prospect on far-field fluorescence profilometry with (sub) nanometer height resolution.

Novel fulleropyrrolidinium‐based materials

The cyclic voltammetry of a series of soluble N-methylfulleropyrrolidinium salts shows that these materials are better electron-acceptors than unmodified C60. The stability of mono-reduced, zwitterionic, and doubly-reduced anionic species, produced either electrochemically or chemically, has been checked by absorption spectroscopy. Langmuir–Blodgett (LB) layers of the C60 derivatives mixed with tricosanoic acid have been built up on different substrates. The optical properties of the films have been characterized using absorption spectroscopy and their structure was investigated by X-ray diffraction.

Preparation of conducting layers of substituted polyacetylenes by solid-phase polymerization of Langmuir–Blodgett layers

UV-initiated polymerization and the properties of the layers composed of the substituted polyacetylene prepared on the basis of tetracosine-2-ol-1. Langmuir–Blodgett (LB) layers have been investigated by means of automatic ellipsometry, IR absorption spectroscopy, IR multiple internal spectroscopy method (IRMIS) and electrophysical measurements. The layers doped with iodine vapour exhibit the conductivity of about 0.05–0.5 Ω −1m −1.

Frenkel excitons in disordered chromophore complexes: Theory of optical absorption of Langmuir–Blodgett layers including pheophorbide-a

Absorption spectra of dye molecules embedded in a Langmuir–Blodgett layer are simulated within a Frenkel-exciton theory. The spectra are determined in using a time-dependent formulation based on the exciton density matrix. Disorder with respect to the positions and the excitation energy of the dye molecules is accounted for within a numerical Monte Carlo treatment. The approach is used to interpret recent measurements on behenic acid layers including pheophorbide-a in a monomeric as well as dimeric form. The concrete type of aggregation and the degree of diagonal disorder can be clarified. Multilayer systems are also discussed.

Rupture of thin wetting films on hydrophobic surfaces. Part II: fatty acid Langmuir–Blodgett layers on glass surfaces

Fatty acid LB-layers were used as model systems for adsorption layers instead of methylated surfaces. Several experimental observations are presented, indicating, that the nucleation of air bubbles might be the reason for the very high rupture thicknesses we observed on such surfaces. This effect is strongly enhanced by collapse structures introduced as additional nucleation sites into the Langmuir–Blodgett-layer. This rupture behavior is in contrast to the results with methylated substrates presented in part I.

Langmuir–Blodgett layers of a coordination polymer with a bifunctional Schiff base

A coordination polymer has been formed at the water surface by reaction of the bifunctional ligand methylenebis( N-hexadecylsalicylidenamine) (MBSH) with bivalent metal ions, dissolved in the subphase. Studies have been carried out to elucidate the structure of this polymer in monolayers at the water surface as well as in Langmuir–Blodgett multilayers. Results with a similar low-molecular compound are included in the discussion. The collapse area in the monolayer at the water surface was strongly dependent on the metal ion concentration. The infrared spectrum of the copper complex Langmuir–Blodgett layer suggests complete conversion of MBSH, since no absorption of the free ligand could be detected. FTIR spectra revealed further, that complexation of copper ions took place between the nitrogen and the oxygen atom of the ligand.

The effect of molecular structure and of three-dimensional order on electron transmission through thin organic layers

The electron transmission through thin organic films was investigated in order to reveal the effect of the chemical nature of the molecules composing the thin organic layer and the role of the three-dimensional structure of the film on the electron transmission efficiency. By preparing Langmuir–Blodgett layers from two types of amphiphile and a film which is a mixture of both, we could vary the chemical properties of the film and the order in the plane perpendicular to the direction of electron propagation. It was found that the electron transmission yield depends on the chemical nature of the film and varies with the film thickness in a non-trivial way. In the case of the mixed film, the electron transmission is reduced dramatically compared to the films composed from one type of molecule. The results are explained by the long wavelength associated with the low-energy electrons.

Determination of structure and shape of nanoclusters obtained in sulphidation of Langmuir–Blodgett layers

It has been shown with the help of ellipsometric and electrophysical measurements that sulphidation of the layers of cadmium, zinc, and lead behenates obtained by Langmuir–Blodgett procedure leads to the formation of non-spherical nanoclusters. The diameter of the formed nanoclusters is 5–10 nm and the thickness is 1.1–1.2 nm. The conductivity of films containing PbS clusters has been shown to depend on illumination.

Photoinduced Electron Transfer between 16-(9-Anthroyloxy)palmitic Acid and Fullerene C60 in Langmuir−Blodgett Films

Langmuir−Blodgett (LB) layers of 16-(9-anthroyloxy)palmitic acid (AA) and C60 mixed with tricosanoic acid have been studied as a model system for photoinduced electron transfer (PET). The PET has been investigated by monitoring the quenching of AA fluorescence in mixed LB films containing different concentrations of C60. Perrin's hard-sphere model adapted for the two-dimensional case provides a good fit to the experimental results, confirming the two-dimensional nature of the system. The critical radius is found to be 11 A.

Physical chemistry of surfaces

Capillarity. The Nature and Thermodynamics of Liquid Interfaces. Surface Films on Liquid Substrates. Electrical Aspects of Surface Chemistry. Long--Range Forces. Surfaces of Solids. Surfaces of Solids: Microscopy and Spectroscopy. The Formation of a New Phase--Nucleation and Crystal Growth. The Solid--Liquid Interface--Contact Angle. The Solid--Liquid Interface--Adsorption from Solution. Frication, Lubrication, and Adhesion. Wetting, Flotation, and Detergency. Emulsions, Foams, and Aerosols. Macromolecular Surface Films, Charged Films, and Langmuir--Blodgett Layers. The Solid--Gas Interface--General Considerations. Adsorption of Gases and Vapors on Solids. Chemisorption and Catalysis. Index.

Quantitative MIR-IR Spectroscopy of Langmuir−Blodgett and Bulk Layers

The possibility of a quantitative IR spectroscopic determination of the mass or thickness of Langmuir−Blodgett (LB) layers directly deposited onto a multiple internal reflection (MIR) element has been investigated. The thickness is calculated from the absorbance (band area) ratios obtained for the LB layer and for a bulk layer of either comparable or a much greater thickness. The basic relations describing the absorbance for different kinds of partial covering of a trapezoidic MIR element are summarized: for the double-sided deposition using the LB technique, for the one-sided deposition of a thin layer achieved by dropping a solution, and for the one-sided deposition of a thick layer. The experiments were performed with octadecyl methacrylate on ZnSe and Ge. A relation is given for the number of reflections for the two-sided covering of the reflection element, typical for the LB technique. The investigations covered all bands in the range from 700 to 2930 cm-1. The set of equations for the absorbances is supposed to be helpful also for the evaluation of other quantitative analysis using the MIR technique.

Quenching of pyrene fluorescence by fullerene C 60 in Langmuir–Blodgett films

Langmuir–Blodgett (LB) layers of pyrene and C 60 mixed with tricosanoic acid have been built-up on quartz substrates. The optical properties of the films were characterized using time-correlated single-photon counting, and absorption and steady-state fluorescence spectroscopy. Observation of negligible overlap between the emission of the donor (pyrene) and the electronic absorption spectra of the acceptor (C 60) indicates that the observed fluorescence quenching of the donor in the presence of the strong acceptor is due mainly to photo-induced electron transfer (PET) with no significant energy transfer process. The PET has been investigated by monitoring the quenching of monomer and excimer pyrene fluorescence in mixed LB films containing different concentrations of C 60.

The role of three dimensional structure in electron transmission through thin organic layers

In this work we probe the effect of the three dimensional structure of the medium on the efficiency of electron transmission (ET) through it, and demonstrate that all three dimensions are playing a crucial role in the ET through thin films. By producing Langmuir–Blodgett layers from two type of amphiphiles we could vary the order in the plane perpendicular to the direction of electron propagation. It was found that the order in this plane affects the low energy electron transmission efficiency. The results are explained by the long wavelength associated with the low energy electrons.

Determining the structure and shape of nanoclusters obtained by sulfidizing Langmuir- Blodgett layers

Determining the structure and shape of nanoclusters obtained by sulfidizing Langmuir- Blodgett layers

The fabrication and evaluation of a vapour sensor based on quartz crystal microbalance coated with poly( o-anisidine) langmuir—blodgett layers

Chemical sensors based on Langmuir—Blodgett (LB) films of poly( o-anisidine) (POA) have been investigated. POA, synthesized by chemical oxidation and mixed with stearic acid, was successfully transferred onto quartz crystal microbalance (QCM) sensors using the LB film technique and used as the active sensing material. The resulting QCM sensor can selectively detect and distinguish among fatty acid vapours such as formic acid, acetic acid, propionic acid and butyric acid. The results suggest that the response of QCM sensors to fatty acids is dependent on both molecular weight and steric hindrance factors. Moreover, the sensitivity of the QCM sensors to different types of organic vapours increases linearly with the number of LB monolayers coated, with a concurrent loss of selectivity.

Polymeric light-emitting diodes from molecularly thin poly(3-hexylthiophene) Langmuir–Blodgett films

Light-emitting diodes based on molecularly thin films of a conjugated polymer have been fabricated. A few Langmuir–Blodgett layers of poly(3-hexylthiophene) have been used as the active emitting material of the devices. Even the thinnest devices with only 3 monolayers, each having a thickness of ≊3 nm, yield the same luminance as thicker ones. The emission results from excitons in the polymer chains, and has a spectrum similar to that of photoluminescence, with a maximum at about 2.0 eV.

SERS and Molecular Orientation in Langmuir−Blodgett Films Deposited onto Smooth Copper Surfaces

Surface-enhanced Raman spectroscopy was applied to the investigation of a hemicyanine dye and a 2-amino-5-nitropyridine derivative as Langmuir−Blodgett layers deposited onto smooth copper surfaces. Raman spectra of neat materials, thin layers, and LB films on Cu surfaces are reported. SERS enhancement was achieved by using colloidal silver. Orientation of the molecules in the LB films and interactions with the metal substrate are discussed.

Study of Langmuir–Blodgett Layers by a Depth-Sensitive Positron Technique

Ferric and magnesium stearate Langmuir–Blodgett films (1) deposited on silica glass were studied by variable-energy positron beam. Positrons signal the presence of the film even after deposition of only 3 monolayers. A signal with 3 and 9% higherSparameter values are characteristic for the ferric and magnesium stearate films, respectively. In addition, positrons were found to be sensitive to the chemical structure of the layers. The results suggest that positron beams could be promising probes of the thickness, composition, and adhesion of Langmuir–Blodgett films.