Spreading behavior of polymerizable monolayers of acrylamides with double alkyl chains and polymerization of the LB films

The spreading behavior of N,N'-dialkylacrylamide (dAAs) monomers on a water surface is investigated by measurement of surface pressure-area isotherms as a function of alkyl chain length and temperature. The monolayers of dAAs can be classified into three types. (I) N,N'-dioctadecylacrylamide (dODA) shows a rapid increase in surface pressure indicating formation of a rigid condensed monolayer; (II) the isotherm of N,N'-dihexadecylacrylamide (dHDA) has a plateau region in surface pressure corresponding to a phase transition from a expanded form to a condensed form, which corresponds to gel-liquid crystal phase transition often observed in biomembranes; and (III) the dialkylacrylamides with alkyl chain length shorter than the hexadecyl group form expanded monolayers with no condensed monolayer at any temperature. The similar three kinds of monolayers are also observed in the isotherms for dHDA monolayer as a function of temperature. It is found that two carbon elongation in double alkyl chains causes the same effect on the monolayer induced by about 10 °C cooling. Under various conditions, only liquid condensed monolayers are transferred on to a solid support, yielding the monomer LB films, practically, of dODA at any temperature and dHDA at low temperature. The polymerization of those LB films by UV irradiation was ascertained by the electronic absorption spectra.     

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.     

Photoinduced energy and electron transfer of covalently linked zinc(II)-pyropheophytin-anthraquinone molecules in monolayers of Langmuir-Blodgett films

Electron donor-acceptor compounds of optically pure covalently linked Zn(II)-pyropheophytin-anthraquinone (ZnPQ) have been synthesized. These compounds allow one to prepare highly ordered solid samples by means of the Langmuir-Blodgett technique. Monolayer films of the P4(S)-ZnPQ diastereoisomer were prepared in a dioleoyl phosphatidylcholine matrix with the concentration varied from 0.5 to 10 mol.%. The time-resolved fluorescence properties of the films were interpreted in terms of the presence of two types of P4(S)-ZnPQ conformers, the folded one and the opened one. The folded conformer predominated and underwent fast intramolecular electron transfer (rate constant > 10¹¹s⁻¹) from the Zn-pyropheophytin part to the anthraquinone moiety and was, therefore, not observed directly in the fluorescence study. The open conformer had a relatively long-lived singlet excited state and was quenched by an energy transfer process to the folded conformer at P4(S)-ZnPQ concentrations higher than 2 mol.% with an estimated quenching radius of 5±0.2 nm.     

Monolayers of triaroylbenzene derivatives

Monolayers of triaroylbenzene derivatives bearing three octyl groups projecting away from the molecular core and terminated by hydroxyl, carboxylic acid, and methyl ester groups have been studied using surface pressure isotherm measurements and Brewster angle microscopy. The octyl derivative lacking a terminal hydrophilic group forms a monolayer of limited stability. The derivatives with hydrophilic end-groups on the octyl chains form stable monolayers. A reorientation at the water surface under compression from a ‘face-on’ to a distorted ‘edge-on’ arrangement appears likely. At intermediate molecular areas, a phase transition occurs and aggregate formation is observed. Studies of mixtures with methyl stearate exhibit a contrast inversion between the background phase and immiscible domains of methyl stearate supporting the concept of a reorientation of the triaroylbenzene derivatives during compression.     

Stability of dimethyldioctadecylammonium bromide Langmuir-Blodgett films on mica in aqueous salt solutions—implications for surface force measurements

Langmuir-Blodgett (LB) monolayer films of dimethyldioctadecylammonium bromide (DDOA) on muscovite mica have been studied using Wilhelmy plate type wetting measurements, surface force measurements, atomic force microscopy (AFM), and Brewster angle microscopy (BAM) on insoluble monolayers of DDOA before deposition. In particular, the effect of exposure to aqueous KBr salt solutions was investigated. BAM shows a heterogeneous monolayer with small condensed domains of dendritic shape under conditions normally used for deposition. A stick-jump behaviour of the meniscus is seen during deposition, leading to a large-scale heterogeneity measurable in wetting studies. These also show breakdown and hydrophilization of the LB film at the three-phase contact line (meniscus) and when exposed to salt solutions of approximately 10⁻² M concentration. The advancing contact angle against water is approximately 105°. Surface force measurements show long-range attraction in water, but also a surface charge which depends on salt concentration, and breakdown when surfaces are brought into contact in high salt concentrations. AFM images of untreated films show small holes, and breakdown when exposed to salt solution, especially at the three-phase line. The LB film is judged to be less suitable as a model hydrophobic surface owing to its heterogeneity and instability in salt solution.     

PEDOT-PSS导电聚合物LB薄膜的制备和性能

研究了十八胺(ODA)及其与硬脂酸(SA)混合单分子膜在导电聚合物聚3,4-乙烯二氧噻吩/聚苯乙烯磺酸(PEDOT-PSS)胶体亚相上的成膜行为和复合LB膜在室温下的电学性能.结果表明:ODA-SA/PEDOT-PSS复合LB膜具有更好的成膜性能,表面粗糙度小且稳定可控,薄膜具有较好的有序结构;ODA-SA/PEDOT-PSS膜电导率高于ODA/PEDOT-PSS复合LB膜,其电导率呈各向异性,水平电导率(σ‖)与垂直电导率(σ⊥)之间相差3～4个数量级,Ⅰ-Ⅴ曲线呈指数关系,为典型的电子隧穿类型.     

Effects of interfacial modification on the performance of an organic transistor based on TCNQ LB films

The influence of interfacial modifications of n-type organic-based thin-film transistors (OTFTs), using low work-function metal electrodes and self-assembled monolayers (SAMs), were analyzed by electrical and structural measurements. We employed ultra thin films of long-alkyl-chained tetracyanoquinodimethane (C₁₈-TCNQ) Langmuir-Blodgett (LB) films as the n-type semiconducting layer with nano-scale thickness. A significant increase in the drain current was observed for the OTFT with low work-function metal electrodes, and this current increase was consistent with the decrease in the injection barrier height for carrier electrons to transfer from the electrodes into the LB films. On the other hand, it was found that the density of interfacial trapping sites decreased with the SAMs treatment, even though no structural modification was induced by the SAM. This behavior is considered to be due to the elimination of active SiOH groups on the SiO₂ substrate by the SAMs treatments. It was also found that the device parameters strongly depend on the alkyl chain length of the SAMs. In order to explain this phenomenon clearly, a new interfacial model based on the interaction between carrier electrons and interfacial SiOH groups is proposed.     

Central metal effect on the organization of porphyrin LB films

Monolayers and Langmuir–Blodgett (LB) films of 5,10,15,20-tetra-4-oxy (2-stearic acid) phenylporphyrin (TSPP) and its complexes TSPPCu(II) and TSPPMn(III)Cl have been studied. π–A isotherms show that the molecular areas of the three molecules are similar to one another, while the polarized UV-vis spectra of the transferred films show different tilt angles of macrocycles with respect to the substrates: TSPP, 31°; TSPPCu(II), 0°; TSPPMn(III)Cl, 52°. The UV-vis spectra show that the π–π interactions between porphyrin macrocycles in monolayers of these three porphyrins are different. The Brewster angle microscopy (BAM) observations suggest that the monolayer behavior is also dependent on the central metal ions. These results indicate that the central metal ions have great influence on the organization of the films.     

A study of Langmuir-Blodgett thin film for organic vapor detection

In this work, arachidic acid was deposited onto a quartz crystal using a standard Langmuir-Blodgett (LB) thin film deposition procedure. Quartz Crystal Microbalance (QCM) technique was used to monitor the reproducibility of the LB film monolayer and was employed to study the organic vapor sensing properties of chloroform, toluene, benzene, ethyl alcohol and isopropyl alcohol. QCM results show that arachidic acid monolayer was successfully organised and deposited from the water surface onto a quartz crystal substrate. This LB film is found to be highly sensitive and selective to chloroform vapor than other vapors. The response of the sample against chloroform is fast, large and reversible.     

Luminescence properties of the Langmuir-Blodgett film of terbium(III) stearoylanthranilate

Terbium(III) stearoylanthranilate has been prepared as a high property Z-type Langmuir-Blodgett (LB) film on various substrates by a vertical transfer process. The UV-visible absorption spectra and the low angle X-ray diffraction peaks have been collected in order to investigate the molecular arrangement and aggregation in the LB films. The average molecular orientation in multilayer stacking was determined by Attenuated Total Reflection Spectroscopy. The influence of the chemical environment of terbium within the LB films on the luminescence properties has been discussed.     

Langmuir-Blodgett films from polyaniline/ruthenium complexes as modified electrodes for detection of dopamine

Langmuir-Blodgett (LB) films from mixtures of polyaniline (PANI) and the ruthenium complex mer-[RuCl₃(dppb)(py)] (dppb=PPh₂(CH₂)₄PPh₂; py=pyridine) (Rupy) were used to modify electrodes and to detect dopamine (DA). The electrochemical response has been used as the principle of detection in order to exploit the molecular-level interaction between PANI and Rupy in the LB films. Cyclic voltammograms were performed in a potential range where the Rupy complex is not electroactive and the response is dominated by the interconversion between the oxidation states leucoemeraldine and emeraldine of PANI. In the presence of DA a further redox pair appears at approximately 230 and 0 mV, associated with oxidation/reduction of DA to dopaminequinone. The current increased linearly in the range between 4.0×10⁻⁵ and 1.2×10⁻³ mol/l. The detection limit for DA concentrations for the 21-layer LB film from PANI/Rupy was 4.0×10⁻⁵ mol/l, which is sufficient to detect DA in a pharmaceutical product. The modified electrode based on PANI/Rupy LB films is selective to DA, particularly because the oxidation potential for DA is lowered, in comparison to a bare indium-tin-oxide electrode. The presence of ascorbic acid, which is an important interferent for DA, could be detected when its concentration was three times that of DA.     

Studies on thin film materials on acrylics for optical applications

Deposition of durable thin film coatings by vacuum evaporation on acrylic substrates for optical applications is a challenging job. Films crack upon deposition due to internal stresses and leads to performance degradation. In this investigation, we report the preparation and characterization of single and multi-layer films of TiO₂, CeO₂, Substance2 (E Merck, Germany), Al₂O₃, SiO₂ and MgF₂ by electron beam evaporation on both glass and PMMA substrates. Optical micrographs taken on single layer films deposited on PMMA substrates did not reveal any cracks. Cracks in films were observed on PMMA substrates when the substrate temperature exceeded 80°C. Antireflection coatings of 3 and 4 layers have been deposited and characterized. Antireflection coatings made on PMMA substrate using Substance2 (H2) and SiO₂ combination showed very fine cracks when observed under microscope. Optical performance of the coatings has been explained with the help of optical micrographs.     

Monomolecular enzyme films stabilized by amphiphilic polyelectrolytes for biosensor devices

This paper describes the use of new amphiphilic polyelectrolytes for protein immobilization. Monomolecular films of glucose oxidase (GO) and monoamine oxidase (MAO) stabilized by amphiphilic polyelectrolytes (polyethyleneimine and poly-4-vinylpyridine derivatives modified by lauryl chains) were formed on a water surface in a Langmuir-Blodgett trough. The compressed films containing the enzymes were transferred onto the surface of a polypropylene membrane of a Clark electrode according to the Langmuir-Schaefer method. The analytical responses of the resulting biosensors were linear over the range 1–10 mM of glucose and 8–100 μM of tyramine. Furthermore, direct functional coupling of GO and ferrocenecarboxylic acid in multilayer films stabilized by amphiphilic polyelectrolytes was demonstrated. The amperometric response of such a sensor was linear over the range 1–20 mM of glucose. The dependence of the kinetic parameters of the enzymes on the amphiphilic polyelectrolyte structures is discussed.     

Fabrication of a stable superhydrophobic film constructed by poly(vinylpyrrolidone)/poly(urushiol)-CuS through layer-by-layer assembly

This article describes a simple stepwise layer-by-layer assembly method to fabricate a stable superhydrophobic film based on urushiol. First, by means of the chelation between Cu(II) and the phenolic hydroxyl group in urushiol (U), urushiol–Cu nanoparticles (U–Cu) were obtained. Then, by the method of layer-by-layer assembly, a hydrophobic film with microstructure was prepared via hydrogen-bonding and coordination between U–Cu and PVP. After introducing S²⁻ into the film, a novel micro- and nanoscale hierarchical superhydrophobic film with a water contact angle of 152° was finally obtained. Due to the unique performances of urushiol, it is believed that the as-prepared surface can be used in the fabrication of chemical engineering materials at broad range.     

Magnetic monolayer film of oleic acid-stabilized Fe3O4 particles fabricated via Langmuir-Blodgett technique

The fabrication of monolayer film of surfactant-stabilized magnetic Fe₃O₄ particles with a size range of 90–150 nm via the Langmuir-Blodgett method is described in this paper. Magnetic Fe₃O₄ particles coated with oleic acid were firstly synthesized by a hydrothermal process, and then the particles were dispersed into chloroform. After that, the Fe₃O₄ suspension was spread to the interface of air/water and transferred to the glass surface. The formation of the Langmuir monolayer of oleic acid-stabilized Fe₃O₄ particles at air/water interface was revealed with the pressure-area isotherm curves. The results of the surface pressure-area isotherm and Atomic Force Microscopy showed that this film is a well compressed monolayer of 2-dimensional Fe₃O₄ particles assembly. Magnetometry results showed that the saturation magnetization of Fe₃O₄ magnetic particles is 86.1 A·m²/kg at room temperature with an applied field of 0.6 T.     

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.     

Preparation and characterization of calix[6]arene Langmuir-Blodgett thin film

Calix[6]arene monolayer/multilayer was prepared on a glass substrate and the behavior of monolayer properties investigated at the air-water interface by taking Langmuir isotherm graph. UV-visible, wettability measurements, atomic force microscopy and quartz crystal microbalance measurements were used to monitor the deposition quality of this Langmuir-Blodgett film. Our results showed that a uniform and high quality film with a transfer ratio of approximately 0.99 occurred using the calix[6]arene material at a deposition pressure of 21 mN/m. The surface free energy was determined to be 25.86 mN/m based on contact angle measurements.     

Ultrathin polymer Langmuir-Blodgett films for microlithography

We describe photolithographic properties of poly(N-dodecylmethacrylamide-co-t-butyl 4-vinylphenyl carbonate) [p(DDMA-tBVPC)], which has a structure being subject to main chain scission and deprotection of t-butoxycarbonyloxy group by deep UV irradiation. Positive-tone patterns of the p(DDMA-tBVPC) Langmuir-Blodgett (LB) film with 60 layers were obtained by deep UV light irradiation followed by development with alkaline aqueous solution. The resolution of the pattern was 0.75 μm, which is the resolution limit of the photomask employed. The etching resistance of p(DDMA-tBVPC) LB film deposited for the pattern of the gold film is also investigated.     

Preparation and properties of multilayer poly(3,4-ethylenedioxythiophene) Langmuir-Blodgett film

Multilayer ultrathin film of poly(3,4-ethylene dioxythiophene) (PEDOT) was fabricated using a modified Langmuir-Blodgett (LB) method. The chemical polymerization of PEDOT occurred in the multilayer nanometer space of an as-prepared LB film by exposing the film to 3,4-ethylene dioxythiophene vapor. UV-Vis-near infrared absorption spectrum and Fourier-transform infrared spectrum techniques were applied to confirm the formation of the PEDOT ultrathin film. The results of atomic force microscopy investigation for the PEDOT LB film showed that the film surface consisted of small clusters having diameters ranging from 50 to 200 nm. X-ray photoelectron spectroscopy and secondary-ion mass spectrometry were employed to analyze the atomic composition of the PEDOT LB film and the location of the formed PEDOT. It was found that the atomic composition of the composite film was almost consistent with the theoretical value, and the PEDOT clusters were well located in different planes of the multilayer structure. The PEDOT LB film exhibited higher conductivity than conventional films and better doping/dedoping characteristics of conductivity. The sensitivity of the PEDOT LB film to NH₃ and HCl gases was also discussed.     

Well-ordered thin films as practical components of biosensors

A Langmuir-Blodgett (LB) film consisting of glutaraldehyde as the binding site for enzyme molecule, an amphiphilic N-alkyl-bis(thiophene)carbazole (BTC7) as the additional electron mediator, and 22-tricosenoic acid (TA) as the matrix for these molecules were deposited on a hydrophilic substrate. Laccase was then covalently immobilized on the film via glutaraldehyde (GA). The sensitivity of this sensor was about twice as high as that of laccase sensor prepared with the same LB film as above but without the bis(thiophene)carbazole derivative. The laccase LB film exhibited enzyme activity.