Langmuir-Blodgett films of oligo- and polythiophenes with well-defined structure

Using terthiophene and its derivatives, quater-, quinque-, sexi-, and - or β-septithiophenes, Langmuir-Blodgett (LB) films including oligo- or polythiophenes with well-defined alignments have been obtained. Esters of terthiophene with a short alkyl chain form stable condensed monolayers on water and can be deposited by the LB method. -polythiophenes without any hydrophilic groups can be incorporated in LB films of mixed monolayers with arachidic acid. In these monolayer assemblies, the long axes of oligo- or polythiophenes stand nearly vertically. LB films of the terthiophene ester derivatives showed a large dielectric constant and a high conductivity which were enhanced by iodine doping.     

DPPC/胆固醇混合LB膜的AFM研究

用LB膜技术将二棕榈酰磷脂酰胆碱(DPPC)和胆固醇的混合液转移到疏水云母上,并利用原子力显微镜(AFM)在空气中表征了LB膜的性质。结果表明,当C(DPPC)∶C(cho lestero l)=2.6∶1,膜压15mN/m时,能形成有缺陷的LB膜。并分析了这种缺陷LB膜的形成过程。此法制得的LB膜接近受损伤的肾上皮细胞膜,用于诱导晶体生长,从而建立受损伤的肾上皮细胞膜导致肾结石形成的化学模型。     

Morphology and electrochemical properties of amphiphilic viologen functionalized multiwalled carbon nanotube hybrids in Langmuir-Blodgett films

Amphiphilic viologens were electrostatically adsorbed on the surface of multiwalled carbon nanotubes (MWCNT) to form viologen-MWCNT hybrids, in which the content of viologens was about 5-10% in weight. Although both viologens and MWCNT hardly dispersed in the water-insoluble organic solvents, the as-prepared viologen-MWCNT hybrids were well dispersed in them with a strong long-term stability, the features of which provided a possibility to prepare their insoluble monolayers at the air-water interface. The surface pressure-area isotherms of these hybrids revealed that they could form stable monolayers, which were transferred on the substrate surfaces by the Langmuir-Blodgett (LB) method. Morphologies of the LB films were characterized by using scanning electron microscopy and atomic force microscopy, the images of which revealed the formation of network two- or three-dimensional films of the functionalized MWCNT. Cyclic voltammograms of the LB films revealed one or two couples of one electron transfer process corresponding to the viologen-MWCNT hybrids with the cathodic and anodic potentials closely related to the alkyl chains of the viologens.     

Photoisomerization of amphiphilic azobenzene derivatives in Langmuir Blodgett films prepared as polyion complexes, using ionic polymers

Polyion complexation in mixed Langmuir and Langmuir Blodgett (LB) films of photochromic amphiphilic azobenzene carboxylic acids, 11-[4-(4-hexylphenyl)azo] phenoxyundecanoic acid, 11-(4-phenylazo)phenoxyundecanoic acid, and diamine grafted poly(methylmethaacrylate) polymers has been studied. Monolayer behaviour of the pure components and mixed films was studied through pressure–area isotherms and LB films were characterized by spectroscopic, X-ray diffraction and Atomic force microscopy techniques. Aggregation (H-type), often observed in LB films of pure amphiphilic azo acids, was partly avoided in the mixed LB films as indicated by absorption spectral studies. Photoisomerization of the polyion complexed LB films was also studied. The results altogether demonstrate that amine grafted polymer enter into a polyion complexation with azo acid carboxylate group. LB films could be obtained by transfer of the composite monolayers and these LB films exhibited different levels of aggregation of the azo acids. Reversible photoisomerization was observed in LB films with unaggregated azo acid.     

Langmuir-Blodgett films of long-chain derivatives of ferrocene, biferrocene and oxidized ferricenium

Different orientations of ferrocene nuclei can be obtained in the Langmuir- Blodgett (LB) films of amphiphilic ferrocene and biferrocene derivatives, depending on the number of long-chain substituents. Polarization energies of ferrocene due to the molecular alignments in the LB films were estimated from UV photoelectron spectroscopy with reference to the cyclic voltammograms for the solutions. Change transfer complexes of the ferrocene derivatives with various electron accepting species such as iodine and tetracyanoquinodimethane give stable condensed monolayers and the electronic absorption spectra of these complexes were examined in the monolayers and multilayers. The BF^-₄ salts of the ferrocene and biferrocene derivatives also form stable monolayers in which the absorption band due to the oxidized ferricenium cation was observed at 610–690 nm. In addition, electrochemical oxidation and reduction for the LB films of the ferrocene derivative have been studied.     

Aggregation of cyanine dyes at Langmuir-Blodgett monolayers

Cyanine dyes are adsorbed from aqueous solution to Langmuir-Blodgett (LB) films, forming monolayers of Scheibe or J aggregates, whereas the dye in solution is in monomeric state. As well as J aggregates other types of aggregates (H, H^* aggregates, oligomers, dimers) can form and interchange at the LB interface depending on conditions and the structures of the dyes and amphiphiles. Reflection spectroscopy proved to be a useful method for studying aggregates and kinetic processes at the air-water interface as the bulk subphase is not recorded by this method.

Aggregation of dyes seems to be controlled by Coulomb interactions and the surface structure of the interacting monolayers. Cationic cyanine dyes are adsorbed only at negatively charged monolayers (e.g. fatty acids) whereas cyanine dyes with negative net charge form aggregates only at positively charged monolayers (e.g. amphiphilic ammonium salts).

Aggregation of cyanine dyes has also been found at LB monolayers of amphiphilic nucleic acids which have been synthesized for the first time. Aggregates of adsorbed cyanine dyes can be transferred to solid substrates by the LB method and investigated by other spectroscopic methods or microscopy.

Adsorption of cyanine dyes at vesicle bilayers has been reported; this was studied by absorption spectroscopy of vesicular dye solutions. Comparison of these spectra with reflection spectra of corresponding LB films reveals significant differences between the effects in LB monolayers and those in vesicular bilayers.     

Chemical sensor based on surface acoustic wave resonator using Langmuir-Blodgett film

A one-port surface acoustic wave (SAW) resonators incorporating Langmuir-Blodgett (LB) films has been investigated. SAW sensors are one potential applications of SAW devices. Most of the work reported on SAW sensor concerns delay lines. In this paper we characterize the mass loading effects of one-port resonators by depositing successive monolayers of LB films onto the surface. A 90 MHz SAW gas-phase sensor has been fabricated on an ST cut quartz substrate, and one-port resonator configurations have been used as the sensing element. Ultra thin monolayers of arachidic acid and arachidic acid ethyl ester have been deposited using the LB method. The resonant frequencies and the Q values have been measured as sensor response. Experimental results show that the Q values and the resonant frequencies of the one-port SAW resonator vary with film mass loading on the SAW device surface.     

Construction and electrochemistry of Langmuir-Blodgett films of fullerene lipid composite/hybrid materials

Studies of the electrochemistry of Langmuir-Blodgett (LB) films of C70/artificial lipids including tridodecylmethylammonium bromide (3C12N+Br-, 1), didodecylphosphate (2C12PO4H, 2), and dioleoylphosphatidylcholine (DOPC, 3) and of LB films of a fullerene lipid (4) bearing triple alkyl chains on a C60 moiety on electrodes were carried out in aqueous media. Stable Langmuir monolayers of fullerene C70/artificial lipid composites and the fullerene lipid (4) were formed at the air-water interface and these monolayers were transferred onto electrodes as LB films. Here, we focus on the importance of cationic matrix lipid films to the facile electrochemistry of C70 embedded in a LB film of cationic lipids on an electrode in aqueous media. On the basis of the electrolyte dependence and the charge dependence of the matrix lipids, a possible electron-transfer mechanism of the C70/artificial lipid LB film-modified electrodes is presented. Electrochemistry of a LB film of 4 was also obtained in an aqueous medium. We demonstrate that the introduction of the chemistry of lipid bilayer membranes to the LB films of fullerenes guides us toward the construction of fullerene/lipid bilayer devices.     

Influences of hydrophilic and hydrophobic substituents on the organization of supramolecular assemblies of porphyrin derivatives formed at the air/water interface

Monolayers and Langmuir–Blodgett (LB) films of several kinds of porphyrin derivatives that have different substituted alkyl chain length, chain numbers and central metals were studied by π-A isotherms, UV–Vis, polarized UV–Vis and fluorescence spectroscopy and low angle X-ray diffractometry (LAXD). The orientation angles of porphyrin rings and alkyl chains were derived from the polarized UV–Vis spectra and LAXD patterns of the monolayers or LB films, respectively. The rings of the freebase porphyrins with different alkyl chain length or number have similar orientation angles in the films due to the same hydrophilic groups on the rings, and those of metal porphyrins have different orientation angles from each other. The orientation of the alkyl chains is related to the special positions of the chains on the rings and the orientation of the rings. The influences of the hydrophilicity of the hydrophilic groups and the alkyl chain number and length on the organization of the supramolecular assemblies of the porphyrin derivatives were discussed.     

Investigation of the monolayer LB film properties of a silsesquioxane hybrid containing phenyl groups using SPM

In this study, we used a silsesquioxane hybrid material between phenyl group containing carbosilane dendrimer and siloxane polymer (G1-3Ph). As expected, G1-3Ph has a networked structure. Generally, it is difficult to generate uniform monolayers as common materials. However, if the materials have a networked structure, we can easily obtain uniform monolayers because of the molecular interactions. Moreover, this networked structure should have a cavity in which ions could be placed.We have fabricated Langmuir–Blodgett (LB) films of the G1-3Ph in a thin film state. We investigated the monolayer behavior using the π-A isotherm at the air–water interface. The π-A curves indicated that the surface pressure of this LB film from the liquid to the solid state falls between 5 and 8 mN/m. The monolayer was deposited onto highly oriented pyrolytic graphite (HOPG) substrates via Y-type deposition at a surface pressure of 5.5 mN/m. We also studied the morphological properties of the silsesquioxane hybrid LB films using SPM and determined the electrical properties of the LB films using STM. The I–V and the morphological characteristics of the sample were investigated at room temperature. The experimental results correlate with the calculated I–V curves when we use the parameters indicated in the caption. This study will enable us to apply a molecular electronic device to measure morphological and electrical characteristics on the nano scale.     

A trough with radial compression for studies of monolayers and fabrication of Langmuir-Blodgett films

A new type of Langmuir trough with radial compression is reported for studies of monolayer properties and fabrication of Langmuir-Blodgett (LB) films. The trough included twenty curved diaphragms, which form a circular shape on water and compress monolayers. Typical monolayers of arachidic acid, DL--phosphatidylcholine dipalmitoyl, cellulose tridecanoate, and poly (butyl methacrylate) showed reproducible surface pressure-area isotherms with radial compression. Flow profiles were studied of monolayers on cellulose tridecanoate and poly(butyl methacrylate) and suggested that the monolayers are radially compressed with no particular film disturbance. A Wilhelmy glass plate preserved no deflection in the subphase surface from low to high surface pressures during the film compression and decompression; no pressure excess causing the deflection, which is frequently observed in the case of the film compression with a sliding barrier, was found on both sides of the Wilhelmy plate. Application of the radial compression enabled to do a symmetrical deposition for the fabrication of LB films.     

Electrode coating with ultrathin films containing electroactive molecules for biosensor applications

Redox molecules, i.e., ferrocene (Fc), ferrocene carboxylic acid (Fc-COOH), and 3-3', 5-5'-tetramethylbenzidine (TMB), are good mediators for typical coenzymes of several dehydrogenases. Such mediators were immobilized in monolayers of dipalmitoylphosphatidic acid (DPPA) by means of the cospreading technique at the water-air interface. TMB was found to interact more strongly than Fc and Fc-COOH with the DPPA matrix; moreover, we observed that DPPA/TMB monolayers could be transferred on different solid supports with the Langmuir-Blodgett (LB) technique. LB films, containing TMB immobilized by means of cospreading and incubation procedure, were characterized recording UV-Vis absorption spectra. Such investigation evidenced the presence of TMB with different oxidation states. Hybrid films containing the mediators were prepared combining two techniques: LB and self-assembly of octadecylmercaptane and octylmercaptane on gold. The resulting structures were characterized by means of ellipsometry and contact angle measurements. Information on the influence of the multilayer structure on the electrode currents and on the redox activity of the immobilized mediators was obtained by cyclic voltammetry. A significant electrochemical signal was observed for TMB included in LB films. The sets of results independently evidenced that TMB can be quantitatively embedded in the ultrathin films of a lipid matrix maintaining its electroactive behavior.     

Distance-dependent energy transfer between indole and anthracene moieties in Langmuir–Blodgett films

1,2-Diphenyl indole (DPI) and 9,10-diphenyl anthracene (DPA) are non-amphiphilic molecules but form excellent LB films when mixed with stearic acid (SA). Spectroscopic investigations of these films indicate formation of aggregates of DPI and DPA in the mixed LB films. DPA has been used as the quencher of the fluorescence of the DPI donor. Distance-dependent energy transfer between donor and acceptor monolayers in the LB film, where they can be precisely separated by inert spacers of stearic acid layers of varied thickness, is shown to satisfy Khun's quadratic equation. This suggests that the donor excitations are delocalized. The large critical transfer distance estimated from the experimental results has been attributed to the formation of aggregates of the molecules in a LB monolayer.     

Experimental studies on substituted copper phthalocyanine Langmuir-Blodgett films

Using the Langmuir-Blodgett (LB) technique, novel copper bis(3-hydroxypropyloxy-hexaisopentyloxy)phthalocyanine molecules were deposited on quartz substrates. It is argued on the basis of pressure-area isotherms that films are deposited as monolayers. Optical absorption spectroscopy suggests that the deposited films were uniform. A.c. measurements were performed on LB films in a planar configuration at different temperatures. The power-law dependence of the conductivity on frequency is explained in terms of electronic conduction through hopping over a coulombic barrier 0.66 eV high. The Debye relaxation time is estimated to be of the order 811 µs at room temperature.     

Investigation of dioctadecyl bilirubinamide in monolayers and Langmuir–Blodgett films

A new amphiphilic ligand, dioctadecyl bilirubinamide [B(CONHR)₂, R=C₁₈H₃₇] form stable monolayers at the air–water interface on neutral, acidic and basic subphases as well as on subphases containing metal ions. Changes in the pH of the subphase do not produce remarkable effects on monomolecular films. The interactions between metal ions and B(CONHR)₂ molecules were investigated by means of various techniques in monolayers and Langmuir–Blodgett (LB) films. B(CONHR)₂ with its complexing head group in contact with the aqueous phase can form metal complexes with many metal ions present in the aqueous phase. The formation of B(CONHR)₂–metal complexes leads to large changes in the area per B(CONHR)₂ molecule. LB films transferred from pure water and metal ions containing subphases were characterized by XPS and low-angle X-ray diffraction.     

Semifluorinated TTF derivatives in Langmuir-Blodgett films

New semifluorinated tetrathiafulvalene (TTF) derivatives were prepared and used in Langmuir and Langmuir-Blodgett (LB) films. Transfer onto a solid substrate of such pure monolayers can be easily achieved leading to organized LB films in which the fluorinated chains are tilted with respect to the normal of the substrate as demonstrated by infrared and X-ray experiments. Doping of such films by iodine does not induce change in the layer spacing on the contrary to already published studies concerning alkyl derivatives of TTF. Such structural stability and values of the layer thickness suggest some interdigitation between TTF groups within the LB film. Depending on the exact chemical structure of the TTF moiety, the iodination is stabilized or not. When the doped film is stabilized in a mixed valency state, conductivity of approx. 10⁻² S cm⁻¹ was measured at room temperature.     

Electrical and photoelectrical transport properties of Langmuir-Blodgett films and a discussion of possible device applications

A rather comprehensive review is given of the electrical and photoelectrical transport properties of Langmuir-Blodgett (LB) built-up monolayers and multilayers. Both conventional (fatty acid) and unconventional materials are included. It is shown that this field has undergone enormous progress in the last few years; many promising scientific areas have opened up and a wide range of device applications can now be considered. The feasibility of several devices using insulating LB films has in fact been demonstrated, and it is now possible to design complex structures and supermolecular “organizates” to fulfil specific “active” electrical functions, and to fabricate them predictably. An extensive review is given of the possible device applications for LB films; these extend from a whole range of electronic devices utilizing the thinness and perfection of insulating LB films, to complex supermolecular structures designed for such purposes as solar energy conversion and high temperature superconductivity. The last possibility is discussed in some detail and is concluded to be a very promising area for future research.     

两亲性聚对苯乙撑的合成及其LB膜研究

本文通过wittig反应合成出了具有两亲性的聚对苯乙撑（PPV）类衍生物,通过核磁和红外对其进行了相关鉴定,并将其铺展上水面上,制得了稳定的单分子膜,并通过计算其单分子面积,研究了其分子在空气／水界面上的取向排列。在对多层LB膜的紫外光谱研究中发现,紫外吸光强度和层数成正比,说明该聚合物的单分子膜在转移过程中膜内分子的取向、构象及堆积方式没有随层数的增加而改变。     

Spectroscopic properties of mixed Langmuir-Blodgett films of rhodamine dyes and poly(N,N-diallyl-N-octadecylamine-alt-maleic acid)

Langmuir-Blodgett (LB) films of poly(N,N-diallyl-N-octadecylamine-alt-maleic acid) as well as mixed films consisting of polyampholyte and two amphiphilic fluorophores - alkyl substituted rhodamine dyes - were prepared and investigated. The π-A isotherm of the polyampholyte at air-water interface is typical for monolayer in the liquid state. Mixed monolayers of polyampholyte and rhodamine amphiphiles show improved packing of the hydrophobic chains. Absorption and fluorescence spectroscopic studies of the mixed LB films reveal the aggregation of dyes in the densely packed multilayer films.     

Second-harmonic generation in Langmuir-Blodgett films of hemicyanine-poly(octadecyl methacrylate) and hemicyanine-behenic acid

Second-harmonic generation (SHG) is used to probe the structure and order in monolayer and multilayer Langmuir-Blodgett (LB) films of highly polarizable dye molecules deposited on glass. Optical measurements on LB monolayers of hemicyanine-poly(octadecyl methacrylate) (PODMA) and hemicyanine-behenic acid mixtures in conjuction with data from compression isotherms show that the hemicyanine-PODMA system is immiscible and that the hemicyanine-behenic acid system is miscible. Incomplete Y-type LB multilayers of 54 mol.% hemicyanine in PODMA exhibited an erratic increase, which was less than linear, in the SHG with the number of layers deposited on the upstroke. Multilayer films of hemicyanine interleaved with behenic acid showed a slightly greater than quadratic increase in SHG with the number of hemocyanine layers deposited.