Transferred Langmuir-Blodgett Films Research Articles

Titania Nanofilms from Titanium Complex-Containing Polymer Langmuir-Blodgett Films.

This paper proposes a method of fabricating low-dimensional TiO2 nanofilms at room temperature under ambient pressure conditions. The titanium-containing polymer complex Ti-p(DDA/acac) was synthesized by reacting an amphiphilic copolymer (p(DDA/acac)) with a titanium complex. Its ultrathin films were prepared using the Langmuir-Blodgett (LB) technique. The monolayer was found to be free from hydrolysis and cross-linking side reactions, even at the air-water interface. The transferred LB films (nanosheets) were oxidized by ultraviolet irradiation at room temperature. The photo-oxidized material has an amorphous and porous structure with subnanometer-scale controllability (0.18 nm per layer). Photocatalytic performance was demonstrated by converting multilayered LB films of Ti-(DDA/acac) and the silicon-containing polymer p(DDA/SQ) into ultrathin hetero-multilayers of TiO2 and SiO2 under UV-O3 treatment. The scalability affords a uniform photopattern formation of photo-oxidized TiO2 films over several hundreds of micrometers.

Self-Assembled Composite Langmuir Films via Fluorine-Containing Bola-Type Derivative with Metal Ions

The design and preparation of functional bolaamphiphile-based composite films are of key importance for application in a wide variety of fields. This study demonstrates a new approach to constructing composite films by the Langmuir-Blodgett (LB) method using a fluorine-containing bola-type diacid derivative with different metal ions. The bola-type molecule we used could be spread on water surfaces and metal ion subphases to fabricate various nanostructured ultrathin films. The obtained data demonstrated that the employed metal ions, including Ag(I), Cu(II), and Eu(III) ions in subphase solutions, can regulate the organized molecular stacking and form interfacial nanostructures deposited in LB films. It was found that the interfacial coordinating interactions can easily occur between carboxyl groups in a molecular skeleton with metal ions in the formed composite films. The formation of composite films was confirmed by changes in the surface pressure-area isotherms, morphologies, and spectra of the transferred LB films. While various research works have achieved the regulation of functions and nanostructures of sophisticated bola-type compounds, we here demonstrate a simple routine to modulate the nanostructures and organized packing of bola-type compounds composite films by changing the metal ions in subphase solutions.

Construction and self-assembly of beta-cyclodextrin derivative composite Langmuir films: Host-guest reaction and nanostructures

The design and preparation of functional beta-cyclodextrin-based composite films are of key importance for wide application fields. This study demonstrates a new route to construct composite films by Langmuir-Blodgett (LB) method via cholesterol-modified beta-cyclodextrin derivative (CD-CHOL). The inclusion complex formation of CD-CHOL and azobenzene derivative (N-Azo) at the air/water interface was investigated. It has been found that the interfacial host-guest recognition could easily occur in the in situ formed CD-CHOL/N-Azo composite films and relatively difficult to occur in the ex situ immersed composite films, because there exist host-guest interaction as well as intermolecular hydrogen bonding interaction. The inclusion complex formation was confirmed by changes in the surface pressure-area isotherms, circular dichroism (CD) and UV–vis spectra of the transferred LB films. And the solvent effect of the composite CD-CHOL/N-Azo films was also investigated, indicating that host-guest interaction between N-Azo and CD-CHOL could occur rather in the nonpolar solvent than the polar solvent. The present research work about beta-cyclodextrin-based composite films by LB method may provide new exploration to prepare organized composite films and demonstrate potential applications in many fields.

Biomimetic monolayer films of monogalactosyldiacylglycerol incorporating ubiquinone

Ubiquinone and plastoquinone are two of the main electron and proton shuttle molecules in biological systems, and monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the thylakoid membrane of chloroplasts. Saturated MGDG, ubiquinone-10 (UQ) and MGDG:UQ mixed monolayers at the air/water interface have been studied using surface pressure–area isotherms and Brewster Angle Microscopy. Moreover, the transferred Langmuir–Blodgett films have been observed by Atomic Force Microscopy. The results show that MGDG:UQ mixtures present more fluid phase than pure MGDG, indicating a higher order degree for the later. It is also observed an important influence of UQ on the MGDG matrix before UQ collapse pressure and a low influence after this event, due to UQ expulsion from the MGDG matrix. This expulsion leads to a similar remaining UQ content for all the tested mixtures, indicating a limiting content of this molecule in the MGDG matrix at high surface pressures. The thermodynamic studies confirm the stability of the MGDG:UQ mixtures at low surface pressures, although presenting a non-ideal behaviour. Results point to consider UQ as a good candidate for studies of artificial photosynthesis.

Dual-Emitting Langmuir−Blodgett Film-Based Organic Light-Emitting Diodes

Langmuir-Blodgett (LB) films containing alternating layers of the metallosurfactants bis(4,4'-tridecyl-2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium(II)-bis(chloride) (1) and bis[2-(2,4-difluorophenyl)pyridine](4,4'-dinonadecyl-2,2'-bipyridine)iridium(III) chloride (2) have been prepared. Langmuir monolayers at the air-water interface of 1 and 2 with different anions in the subphase have been characterized by pi-A compression isotherms and Brewster angle microscopy (BAM). The transferred LB films have been characterized by IR, UV-vis and emission spectroscopy, and atomic force microscopy (AFM). Electroluminescent devices formed by LB films containing alternating layers of these two molecules show dual emission by simple mixing of the two emitters in a single LB film, and by preparing two stacked configurations, in which a LB layer of the ruthenium complexes is deposited on top of a LB layer of the iridium complexes and the inverse situation. The color of the electroluminescence can be tuned by changing the thickness of each LB layer. Due to efficient hole blocking of a layer of the iridium complexes when deposited on top of the layer of ruthenium complexes, in that configuration the green emission of the iridium complexes is suppressed. In the opposite case, excitons are generated in both layers although most likely preferentially in the layer of the iridium complexes.

Dual-Emissive Photoluminescent Langmuir−Blodgett Films of Decatungstoeuropate and an Amphiphilic Iridium Complex

Langmuir monolayers and Langmuir-Blodgett (LB) films of the decatungstoeuropate [Eu(W(5)O(18))(2)](9-) (EuW(10)) and the amphiphilic Ir complex 1 have been successfully fabricated by using the adsorption properties of the EuW(10) polyanion dissolved in the aqueous subphase onto a positively charged 1 monolayer at the air-water interface. The compression isotherms and Brewster angle microscopy (BAM) of monolayers of 1 on pure water (1 monolayer) and on a subphase containing 10(-6) M EuW(10) and 10(-3) M NaCl (1/EuW(10) monolayer) have been studied. Infrared and UV-vis spectroscopy of the transferred LB films indicate that EuW(10) and 1 molecules are incorporated within these LB films. X-ray reflectivity (SXR) and atomic force microscopy (AFM) experiments indicate that LB films of 1 present a heterogeneous morphology while 1/EuW(10) films show a flatter and more homogeneous surface as well as a layered structure with a periodicity of 4.1 nm. Mixed monolayers of 1 and DODA (dimethyldioctadecylammonium bromide) have been prepared with EuW(10) polyanions in the subphase to control the concentration of 1 and EuW(10) polyanions within the LB films. AFM and SXR experiments with the transferred LB films show that the dilution of 1 with DODA improves the layered structure. The luminescence of 1 is partially quenched by EuW(10) in the 1/EuW(10) LB films, while emission from EuW(10) is not detected. On the other hand, emission from both entities is preserved in the LB films prepared from mixed DODA/1 monolayers, in which the red and yellow emissions arise independently from EuW(10) and 1, respectively. The different DODA:1 ratios lead to changes in the emission color. Therefore, they constitute a promising color-tunable luminescent material.

Aligned single-walled carbon nanotubes by Langmuir–Blodgett technique

Single-walled carbon nanotubes (SWNTs) were chemically functionalized with amphiphilic octadecylamine after purification. Lower density and highly oriented SWNTs were obtained via Langmuir–Blodgett (LB) technique. A model was introduced to explain the compression-induced alignment. The phase behavior of the spreading monolayer was studied by surface pressure-area isotherms at different temperatures and different compression speeds. The transferred LB films of SWNTs with different mean lengths were investigated by the field emission scanning electron microscopy, showing that SWNTs with average length at 1000–2000 nm have more preference of reorientation upon compression than shorter ones (∼500 nm), while SWNTs that are too long (∼3000 nm) would tangle together and the reorientation is weaker. Multilayers (up to 18 layers) of SWNTs were obtained with high transfer ratios (>0.93) and the UV-vis absorption spectra indicated that the layer-by-layer deposition was successful.

Interfacial Assembly of an Achiral Zinc Phthalocyanine at the Air/Water Interface: A Surface Pressure Dependent Aggregation and Supramolecular Chirality

The aggregation and supramolecular chirality of the interfacial assemblies of an achiral phthalcyanine derivative, zinc 2,3,9,10,16,17,23,24-octakis(octyloxy)-29 H,31 H-phthaloxyanine (ZnPc), were investigated, and a surface pressure dependent behavior was observed. It was found that ZnPc could be spread as a Langmuir film on water surface and transferred onto solid substrates by the horizontal lifting method. The compound formed mixed J- and H-aggregates in the transferred Langmuir-Blodgett (LB) films. Deconvolution of the broaden Q-band revealed three main components of the spectra, which corresponded to H- and J-aggregates and medium transition aggregates, whose relative contents could be modulated by the surface pressure at which the films were transferred. On the other hand, the transferred LB films composed of these aggregates showed Cotton effects in circular dichroism spectra when the floating film was compressed over a certain surface pressure although the compound itself was achiral. The cooperative arrangement of the macrocylic ring in a helical manner through the interfacial organization was suggested to be responsible for such optical activity in the LB films. A possible explanation based on the cooperative arrangement of the ZnPc building blocks in a helical sense stacking in the aggregates was proposed.

Preparation and electrochemical properties of organic–inorganic hybrids with the use of alkylammonium or alkylviologen cations and polyoxometalate anions

We report preparation of organic–inorganic hybrids by using Langmuir monolayers of several alkylammonium derivatives and a viologen cation as templates at the air–water interface. Surface pressure area isotherms indicated that, although the alkylammonium with four long-chains is able to form stable monolayer on the pure water surface, it is difficult to form on the 0.1 mmol/L polyoxometalate (H 3PMo 12O 40) subphase surface; reversely, although the alkylammonium and the viologen with one long-chain unable to form stable monolayer on the pure water surface, it becomes stable on the 0.1 mmol/L H 3PMo 12O 40 subphase surface. The hybrids were transferred onto solid supports by Langmuir–Blodgett (LB) method and characterized by X-ray photoelectron spectroscopy. Electrochemical measurements of the transferred LB films showed reversible three redox couples between 400 and −200 mV for the alkylammonium–polyoxometalate hybrids, and four redox couples between 400 and −520 mV for the alkylviologen–polyoxometalate bifunctional hybrid.

Thin Films of Polymerized Rodlike Phthalocyanine Aggregates

We report here the synthesis, characterization, and thin film formation of a polymerizable octa-substituted phthalocyanine (Pc) with styryl-terminated side chains, CuPc(OCH2CH2OCH2CHCHPh)8, 2,3,9,10,16,17,23,24-octakis(2-cinnamyloxyethoxy) phthalocyaninato copper(II) (1). We compare this Pc with a previously discussed phthalocyanine, also possessing styryl groups at the termini of the side chains, but with one alkoxy group in the side chain removed, CuPc(OCH2CH2CHCHPh)8 (2) (J. Am. Chem. Soc. 2001, 123, 3595). Both 1 and 2 are related to the octa-substituted phthalocyanine CuPc(OCH2CH2OBz)8, 2,3,9,10,16,17,23,24-octakis (2-benzyloxyethoxy) phthalocyaninato copper(II) (3), which has been shown to form highly coherent rodlike aggregates in Langmuir−Blodgett (LB) films, with excellent control of rod orientation (J. Am. Chem. Soc. 1999, 121, 8628; Langmuir 2001, 17, 7071). Irradiation of the styryl π−π* absorbance bands (254 nm) for horizontally transferred LB films of 1 and 2 results in stabilization of thei...

Conducting Langmuir-Blodgett (LB) films derived from a new tetrathiafulvalene(TTF) derivative with pyridine groups

A new tetrathiafulvalene(TTF) derivative - 4,5-bismethylthio-4',5'-bis(3-picolylthio)-tetrathiafulvalene (BMP-TTF) bearing pyridine groups was found to form stable monolayers at the air/water interface with or without the presence of AgNO 3 . The monolayers can be transferred onto solid substrates with LB technique. Surface pressure-area isotherms, UV-vis spectrum, FT-IR, X-ray photoelectron spectroscopy. and X-ray diffraction were used to characterize the monolayer formation and the transferred LB films. The room temperature conductivities of the LB films are about ∼10 -7 S.cm -1 and after iodine doping, they are increased to ∼10 -3 S.cm -1 .

Spreading monolayers and Langmuir–Blodgett films of a novel type of optically active macrocyclic poly(ether sulfone)s containing 1,1′-bi-2-naphthol moiety

Aimed at investigating the monolayers and Langmuir–Blodgett (LB) films of compounds without any substituted alkyl chains and constructing chiral ultrathin films, a new group of optically active macrocyclic poly(ether sulfone)s containing a binaphthyl group, which have no substituted alkyl chains, were synthesized. The spreading behavior and the ultrathin film fabrication of these compounds was studied. Stable monolayers with collapse surface pressures up to 40 mN m −1 were formed at the air/water interface and uniform LB films were fabricated by using the horizontal lifting method. The optical activities of the compounds were maintained in the LB films. Transferred LB films were characterized by UV-vis, fluorescence and circular dichroism spectroscopy. It was found that the 1B b, 1L a and 1L b bands of the compounds showed a red shift compared with the corresponding solutions. While no split of the Cotton effect was observed for the dimeric compound, strong exciton couplings that could be ascribed to the interactions between the naphthyl groups were observed for the trimeric macrocyclic compounds.

Monolayers and Langmuir–Blodgett films of optically active macrocyclic poly(esters) containing the 1,1′-bi-2-naphthol moiety at the air/water interface

In order to fabricate chiral Langmuir–Blodgett (LB) films and expand the range of monolayer-forming materials, a new type of macrocyclic poly(aryl ester) containing the optically active 1,1′-bi-2-naphthol group, and which have no substituted alkyl chains, were investigated. The spreading behaviors and the fabrication of ultrathin films of the compounds were studied. Stable monolayers were formed with collapse surface pressures up to 40 mN m−1 at the air/water interface, although these compounds have no substituted alkyl chains. It is suggested that in the monolayers the macrocyclic rings lie flat on the surface of the water, while the aromatic rings extended upwards out of the water surface. The monolayers can be transferred onto solid substrates uniformly using the horizontal lifting method. Transferred LB films were characterized by UV, polarized UV and circular dichroism (CD) spectra. In comparison with the corresponding solutions, the 1Bb and 1La bands of the compounds in LB films show a red shift. Both the UV and polarized UV spectra indicate a J-like aggregation of the chromophores in the LB films. In the CD spectra, splitting of the Cotton effect is observed both in solution and in LB films, indicating that interactions between the neighboring naphthalene chromophores take place. In the LB films, the exciton couplet shows a red shift in comparison with those in solution due to aggregation.

Implications of using m-cresol in the Langmuir–Blodgett processing of polyaniline

The use of m-cresol for the Langmuir–Blodgett (LB) processing of polyaniline has been investigated, in particular for probing possible secondary doping processes in LB films. Langmuir monolayers and LB films of polyaniline and polyaniline–cadmium stearate composites have been obtained with the use of camphor sulfonic acid (CSA) both in the presence and absence of m-cresol in the spreading solution. Expanded monolayers with higher molecular areas have been observed upon employing m-cresol. The UV-vis spectral changes for the polyaniline LB films caused by m-cresol were shown to depend both on the preparation conditions and on the doping state of the monolayer. Such effects are likely to originate from changes in molecular conformation since m-cresol is not retained in the transferred film. In addition, processing with m-cresol brought no change to the electrical conductivity nor to the stacking order of cadmium stearate domains in the transferred LB films.

LB films of non-amphiphilic diacetylene-1,4(bis-(3-quinolyl)-buta-1,3-diyne (DQ)

In the present work, Langmuir–Blodgett (LB) processing of a non-amphiphilic monomer, 1,4-bis(3-quinolyl)-buta-1,3-diyne (DQ) and the attempts to obtain PDQ LB films from DQ LB films are presented. LB processing has been carried out with pure DQ and of DQ mixed with arachidic acid and 10,12-pentacosadiynoic acid. Characteristics of pure and mixed monolayers were studied by π–A isotherm and the transferred LB films were characterized by UV-visible spectroscopy, X-ray diffraction (XRD) and UV-irradiation studies. Results show that, in contrast to its bulk reactivity, DQ does not undergo DQ→PDQ conversion in the LB film structure. Preparation of PDQ LB films from PDQ monolayer has also been discussed.

Preparation of Langmuir−Blodgett Films of Soluble Polypyrrole

Stable monolayers of soluble parent polypyrrole (Ppy) and mixed monolayers of cadmium stearate and Ppy were studied for the first time using surface pressure and surface potential isotherms. Ppy was obtained by chemical polymerization of the pyrrole monomer in the presence of dodecylbenzene sulfonic acid and characterized by ultraviolet−visible (UV−vis), Fourier transform infrared (FTIR), and elemental analysis techniques. Pure Ppy monolayers could only be transferred if optimized experimental conditions were employed, but mixed monolayers could be easily transferred in the form of Y-type Langmuir−Blodgett (LB) films, with a uniform layer-by-layer transfer according to UV−vis results. The FTIR spectrum indicated the presence of cadmium stearate along with Ppy. X-ray diffraction patterns showed the presence of cadmium stearate domains. The transferred LB films were characterized by electrical conductivity, cyclic voltammetry, and surface potential measurements.

Evaluation of collector adsorption phenomena by FT-IR/IRS examination of transferred LB films

The transfer of Langmuir-Blodgett (LB) monolayers of collector molecules to the surface of mineral crystals is an excellent method for the study of collector adsorption phenomena and is of particular significance in the understanding and development of improved flotation separations. The fatty acid/fluorite and amine/sylvite flotation systems were investigated by the Fourier transform-infrared/internal reflection spectroscopy (FT-IR/IRS) examination of transferred LB monolayers of collector molecules at the surfaces of the mineral crystals. The π-A isotherm study of fatty acid and amine, typical anionic and cationic collectors, showed the different packing trends dependent upon the pH and/or type of subphase. This result clearly reflects the effect of pH on compound formation and dissociation of the collector molecules. Identification of the collector adsorption state and confirmation of the validity of the FT-IR/IRS adsorption density equation were included in this research effort. This allowed for a detailed discussion of collector adsorption phenomena. As a result of these experiments, it is possible to relate the hydrophobic character of a surface to the nature of the adsorbed collector structure and thus describe flotation behavior in greater detail. For example, it appears that in the case of oleate/fluorite the equivalent of an LB monolayer can form spontaneously during adsorption from solution, and this structure is known as a self-assembled monolayer (SAM). Such a state is significantly more hydrophobic than the oleate structure which forms on the calcite surface at an equivalent adsorption density.

Inhomogeneities of phase separated Langmuir–Blodgett films studied by atomic force microscopy

Micromorphology of phase separated Langmuir–Blodgett (LB) films is investigated by atomic force microscopy from submicrometer scale up to 100 μm scale. Several novel phenomena are revealed: (a) the existence of grains with the size of 20–100 nm in diameter in the liquid expanded phase; (b) the existence of a rough domain boundary with fingerlike structures and (c) an inhomogeneous distribution of holelike defects in the liquid condensed domains. Aging effects are studied systematically, which give the hint for the existence of water on transferred LB films. The results are relevant to the understanding of the early stages of the domain formation and the two-dimensional nucleation processes.