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.     

Study of electrical polarization hysteresis in ferroelectric polyvinylidene fluoride films

Electric properties of polyvinylidene (PVDF) films fabricated using the Langmuir-Schaefer method have been studied. Films of different thickness were deposited on silicon substrates and analyzed using several techniques. X-ray diffraction (XRD) data showed that PVDF films crystallize at an annealing temperature above 130 °C. Polarization versus electric field (PE) ferroelectric measurements was done for samples prepared with electrodes. PE measurements show that the coercivity of the films increases as the maximum applied electric field increases. The coercivity dependence on the frequency of the applied electric field can be fitted as f^0.6. The results also show that the coercivity decreases with increasing the thickness of PVDF film due to the pinning effect.     

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.     

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.     

Thin films of liquid crystal fumarates and a related acrylate

Five fumarate esters and one acrylate ester have been synthesized and their properties examined. Four of them can be deposited as multilayers by evaporation in vacuo, and three of this group behave as thermotropic smectic liquid crystals. We have attempted to stabilize the homeotropic smectic phase by polymerizing the film using UV light. In two cases we have been successful and have produced films which are resistant to prolonged heating in THF. We infer that these materials are both polymerized and cross linked. They retain their regular layer structure after polymerization, a behaviour which we have demonstrated by X-ray diffraction. We have also attempted to form Langmuir-Blodgett multilayers with these compounds and in four cases have been successful.     

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.     

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.     

Structures and vapor-sorption characteristics of sputtered polychlorotrifluoroethylene films treated by hydrogen-plasma

Hydrogen-plasma treatment of the polychlorotrifluoroethylene (PCTFE) film produced by radio-frequency sputtering induces considerable elimination of halogen (fluorine and chlorine) atoms. This dehalogenation produces some noteworthy structural features: surface densification (crosslinks), trapped radicals, and incorporation of oxygen in the carbon networks. These structural changes modify the vapor-sorption properties of the sputtered PCTFE film, producing a molecular-sieving effect and enhancing the polar character of solubility properties of organic vapors.     

Photopatterning of heterostructured polymer Langmuir-Blodgett films

Heterostructured polymer Langmuir-Blodgett (LB) film prepared by using poly(N-dodecylacrylamide-co-t-butyl 4-vinylphenyl carbonate) (p(DDA-tBVPC53)) and poly(N-neopentyl methacrylamide-co-9-anthrylmethyl methacrylate) (p(nPMA-AMMA10)) polymer LB films which can act as photogenerator layers were investigated. Patterns with a resolution of 0.75 μm were obtained on heterostructured polymer LB films composed of 4 layers of p(nPMA-AMMA10) LB film (top layers) and 40 layers of p(DDA-tBVPC53) LB film (under layers) on a silicon wafer by deep UV irradiation followed by development with 1% tetramethylammonium hydroxide aqueous solution. The sensitivity of the heterostructured polymer LB films was improved without loss of the resolution compared with p(DDA-tBVPC53) LB film. The etch resistance of the heterostructured polymer LB films was sufficiently good to allow patterning of a copper film suitable for photomask fabrication.     

Monoparticulate films of polyaniline

Monoparticulate films were prepared from colloidal polyaniline (PANI) via the Langmuir-Blodgett (LB) technique. An aqueous dispersion of PANI obtained by aniline polymerization in the presence of polyvinyl alcohol was spread at the air-water interface in a LB trough. The floating films were transferred by the vertical lifting method to Si wafer or glass substrates. The films were very stable and could not be removed during immersion in aqueous solutions for at least several months. The color of dry monoparticulate PANI films was violet independently of the color adapted upon immersion in aqueous media at different pH. We suggest that not only the wavelength of the absorbed light, but also that of the scattered light, has an effect on the color of PANI.     

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.     

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.     

Sensing properties of two-component Langmuir-Blodgett layer and its porous derivative in SAW sensor for vapors of methanol and ethanol

Two-component Langmuir-Blodgett film has been fabricated from equimolar mixture of 5-[[1,3-dioxo-3-[4-(1-oxooctadecyl)phenyl]propyl]amino]-1,3-benzenedicarboxylic acid with cetylamine. Porous one-component derivative of this film has been obtained by removing of cetylamine. Both films have been investigated as sensing layers of the surface acoustic wave sensors for vapors of methanol and ethanol in air. These films react on the alcohol vapors. Time of the sensor reaction is less than 2 s and this reaction is reversible. The response parameters of the sensor depend on the kind of the alcohol and the structure of the layer. An explanation of the observed differences in the behavior of both layers in contact with vapors of the alcohols has been proposed.     

Matrix-assisted pulsed laser deposition of polymer and nanoparticle films

Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was used to deposit films of Poly(9,9-dioctylfluorene) - PFO and Methoxy Ge Triphenylcorrole [Ge(TPC)OCH3]. The PFO was dissolved in different matrices, like chloroform-CHCl3, tetrahydrofuran - THF and toluene with a 0.5 wt % concentration, while Ge(TPC)OCH3 was diluted in THF with a concentration of 0.01 wt %. The frozen targets were irradiated with a KrF excimer laser. The, films presented good emission properties to be exploited in light emitting devices and gas sensors based on luminescence quenching. The working principle of the MAPLE technique was used for the deposition of colloidal nanoparticles and nanorods, too. TiO2 colloidal nanoparticles (diameter: ∼10 nm) and nanorods (diameter: 5 nm; length: 50 nm) were diluted in deionised water (0.02 wt %) and toluene (0.016 wt %) respectively. The deposited nanostructures preserved dimensions and structural properties of the starting particles and the films showed very interesting electrical responses when exposed to oxidizing gases for sensing applications.     

Self-quenching of a photo-excited ruthenium complex in component-controllable mixed Langmuir-Blodgett films

The miscibility and phase behavior of the mixed monolayer of Ru(dpphen)₃²⁺ (dpphen=4,7-diphenyl-1,10-phenanthroline) (abbreviated as Ru(II)), octadecyltrichlorosilane (OTS) and stearic acid (SA) at air/water interface had been investigated in detail. Two-dimensional density of Ru(II) could be easily adjusted by changing the mixing ratio of Ru(II)/SA/OTS. The mixed monolayer of Ru(II)/SA/OTS with different molar proportions had been deposited and characterized by low angle X-ray diffraction, UV-visible absorption spectra and photo-induced emission spectra. The possible structure of its resulting LB film was proposed based on the results of the π-A isotherms and low angle X-ray diffraction. Photo-induced electron transfer and self quenching of Ru(II) in mixed LB films had been investigated in detail.     

一种新型可溶喹吖啶酮衍生物LB膜的制备及其光谱特性

采用表面压-分子面积(π一A)等温曲线和紫外-可见吸收谱的方法研究了一种新型喹吖啶酮衍生物材料LB膜的制备及其光谱特性．实验表明,这种新型喹吖啶酮衍生物能够在水面上形成稳定的单分子膜,它与花生酸(AA)混合后不仅可以形成很好的单分子膜,而且可以较好地转移到固体基片上制备成LB膜多层膜．这种新型喹吖啶酮衍生物LB膜的紫外-可见吸收谱的吸收峰位较稀溶液发生了红移,这是由极性溶剂分子与其相互作用的结果．它在溶液和LB膜中都是以单体的形式存在．     

Photochromism induced magnetization changes in Prussian Blue ultrathin films fabricated into the Langmuir-Blodgett films composed of an amphiphilic azobenzene and a deoxyribonucleic acid

A photomagnetic ultrathin film consisting of an azobenzene, a deoxyribonucleic acid, and Prussian Blue has been fabricated by the Langmuir-Blodgett method. Prussian Blue layers in the films were a two-dimensional structure with the height of 50 Å and the average coherence length of 210 Å. Reversible photoisomerization of the azobenzenes was observed even in the films. The films exhibit the long-range ferromagnetic order below 4.2 K and moreover, upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 1.0%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization.     

Molecular order in Langmuir-Blodgett assembled films of an azobenzene amphiphile

Alternating multilayers of amphiphile, 4-{4-[Methyl-(4-octadecylcarbamoyl-butyl)-amino]-phenylazo}-benzenesulfonic acid (S-azo-C₁₈), and stearic acid were deposited on hydrophobized silica surfaces using the Langmuir-Blodgett technique. Ellipsometry, UV-visible spectroscopy, and second harmonic generation were used to characterize the films, demonstrating reproducible deposition and suggesting a well ordered film structure. Despite the appearance of order at the macroscopic level, neutron and X-ray scattering results unequivocally show that there is considerable disorder, with significant interpenetration between the stearic acid and S-azo-C₁₈ layers. These results suggest that molecular disorder in Langmuir-Blodgett deposited multilayer films may often go unrecognized mainly because the macroscopic probes based on these optical measurements are not adequate for determining the molecular level structural order.     

Polymer microspheres stabilized by titania nanoparticles

Polymer microspheres stabilized by titania nanoparticles were synthesized using a two-step Pickering emulsion polymerization process, in which nanosized titania nanoparticles were used as solid emulsifiers and building blocks. It gives a simple but novel route for the fabrication of functional inorganic/polymer hybrid materials with controlled microstructures. The final Pickering emulsion can be applied to various substrates forming continuous films with highly ordered nanosized to microsized TiO₂ protuberances across the films. Those films will have potential applications for photo-catalyst, water and air purification.     

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.