Y-type Langmuir-Blodgett Films Research Articles

Surface Chemistry Studies on the Formation of Mixed Stearic Acid/Phenylalanine Dehydrogenase Langmuir and Langmuir-Blodgett Films.

This work investigates the physicochemical properties of mixed stearic acid (HSt)/phenylalanine dehydrogenase enzyme (PheDH) Langmuir films and their immobilization onto solid supports as Langmuir-Blodgett (LB) films. PheDH from the aqueous subphase enters the surfactant matrix up to an exclusion surface pressure of 25.3 mN/m, leading to the formation of stable and highly condensed mixed Langmuir monolayers. Hydrophobic interactions between the enzyme and HSt nonpolar groups tuned the secondary structure of PheDH, evidenced by the presence of β-sheet structures as demonstrated by infrared and circular dichroism spectra. The floating monolayers were successfully transferred to solid quartz supports, yielding Y-type LB films, and then characterized employing fluorescence, circular dichroism, and microscopic techniques, which indicated that PheDH was co-immobilized with HSt proportionally to the number of transferred layers. The enzyme fluidized the HSt monolayers, reducing their maximum dipoles when condensed to their maximum, and disorganized the alkyl chains of the fatty acid, as detected with infrared spectroscopy. The stability of the mixed floating monolayers enabled their transfer to solid supports as LB films, which is important for producing optical and electrochemical sensors for phenylalanine whose molecular architecture can be controlled with precision.

Cellulose Nanofiber Nanosheet Multilayers by the Langmuir–Blodgett Technique

We describe a systematic approach for producing cellulose nanofiber (CNF) nanosheets using the Langmuir-Blodgett (LB) technique. The CNFs were obtained from sulfuric acid hydrolysis of commercially available microfibrillated cellulose. Needle-like CNFs, negatively charged by grafted sulfate groups, were maintained at the air-water interface, assisted by amphiphilic polymer, poly( N-dodecyl acrylamide) (pDDA). The CNFs produced a stable monolayer. The surface pressure increased steadily with a high collapse pressure of 50 mN m-1 when spread with formic acid and pDDA. The composite monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. Upstroke and downstroke transfer ratios of the films were, respectively, unity and 0.88, indicating that full coverage was achieved by the monolayer even for more than 200 layers. Results obtained using atomic force microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy showed that CNF nanosheets possess well-defined layer structures with average monolayer thickness of 5.3 nm. The relative amount of CNFs in the nanosheets was calculated as 62.6 wt % using the quartz crystal microbalance technique. The as-prepared nanosheets are optically transparent to visible light and have high hydrophobicity. In fact, the nanosheet transparency was higher than 88% at 600 nm wavelength for 24 layers. A miniscule amount of pDDA enables demonstration of free-standing CNF nanosheets with 1 cm width and 45.6 nm thickness (23 layers).

Effect of chemical structure of fluorinated polyhedral oligomeric silsesquioxanes on formation of Langmuir monolayers and Langmuir-Blodgett films

Fluorinated polyhedral oligomeric silsesquioxanes (F-POSS) due to their nanoscale hybrid structure coupled with hydrophobic substituted chains have drawn significant attention as highly hydrophobic and oleophobic materials. That is why the surface properties of such compounds at the molecular level should be analyzed in details. Therefore we studied four different fluorinated closed cage polyhedral oligomeric silsesquioxanes (POSS) using Langmuir and Langmuir-Blodgett (LB) techniques. The monolayer behavior was investigated by measurements of the surface pressure-area (π-A) isotherm and morphology of the films was visualized using Brewster angle microscopy (BAM). The rheological behavior was investigated using interfacial shear rheometer (ISR). The unusual properties of these silsesquioxanes result from their unsymmetrical structure. The hydrophobic character of their fluorinated substituents, combined with the hydrophilicity of the trimethoxysilane moieties lead to specific monolayer properties. The compounds were found to form stable monolayers at the air/water (A/W) interface however the surface activity of POSS derivatives decreases with increasing content of fluorinated moieties in the POSS structure. The monolayers of the studied POSS compounds were also successfully transferred onto the solid substrates as Y-type Langmuir-Blodgett films. The wettability and the structure of the LB film were investigated by measuring the static water contact angle on the glass surface. The presence of fluorinated moieties in the structure of POSS molecules governs the enhanced hydrophobic properties of solid substrate modified by the LB film.

Molecular organization and doping in poly(2-methoxyaniline)/Ni(dmit)2 films obtained with the Langmuir–Blodgett technique

The control of the properties of materials at the molecular level is pursued for many applications, especially those associated with nanostructures. In this paper, we show that the coordination compound [Ni(dmit)2], where (dmit) is the 1,3-dithiole-2-thione-4,5-dithiolate ligand, can induce doping of poly(2-methoxyaniline) (POMA) in molecularly ordered Langmuir and Langmuir–Blodgett (LB) films. Doping was associated with interactions between the components and the compression of the Langmuir film at the air–water interface, according to polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data. Taking these results together with in situ UV-Vis absorption measurements, we could identify the molecular groups involved in the interaction, including the way they were reoriented upon film compression. The Langmuir films were sufficiently stable to be transferred as Y-type LB films, while the hybrid POMA/[Ni(dmit)2] films remain doped in the solid state. As expected, the molecular charges affected the film morphology, as observed from combined atomic and electric force microscopy measurements. In summary, with adequate spectroscopy and microscopy tools we characterized molecular-level interactions, which may allow one to design molecular electronic devices with controlled electrical properties.

Photolithography and Photochemical Reaction of Copolymer Containing Anthracene in Langmuir-Blodgett Films

A series of copolymer containing photoactive anthracene group, poly(N-dodecylmeth- acrylamide-co-anthrylmethylacrylate) p(DDMA-co-AnMA) were synthesized. Their molecular arrangement and photolithographic properties in Langmuir–Blodgett (LB) films were investigated. The copolymer p(DDMA-co-AnMA) could form stable monolayer at air/water interface and could be transferred onto solid supports, giving Y-type uniform LB films. The result showed that the irradiation with difference light wavelength leaded to changes of copolymer LB films in their chemical structure, concerning only the anthracence unit. When irradiated at 248 nm, the anthracene acted as photodecomposition group because of the peroxides. On the other hand, the main photoreaction induced by 365 nm is dimerization of anthracene. As a result, posotive-tone and negative-tone pattern could get by choosing a suittable irradiation light wavelength. Etching resistance of p(DDMA-AnMA) LB films was also investigated in a nanometer regime permitting etching of gold.

Oligonucleotide-Based Amphiphilic Block Copolymers Interacting with Cell Membrane Models at the Air-Water Interface

Oligonucleotides have exceptional molecular recognition properties, which are involved in biological mechanisms such as gene silencing or cell-surface receptor recognition. In many cases, the cell membrane structure is barrier to investigate their use in human therapy for drug or gene delivery. However, this can be obviated by grafting a hydrophobic tail to the oligonucleotide. In this present work, we demonstrate that two oligonucleotides, one consisting of 12 guanosine units (G12), and the other one consisting of five adenosine and seven guanosine (A5G7) units, when functionalized with poly(butadiene), namely PB-G12 and PB-A5G7, can be incorporated into Langmuir monolayers of dipalmitoyl phosphatidyl choline (DPPC), which served as a cell membrane model. With surface pressure and surface potential-area isotherm, we observed that PB-G12 and PB-A5G7 affect the DPPC monolayer, even at high values of surface pressure. The effects from PB-G12 were consistently stronger, particularly in reducing the surface compressibility of the DPPC monolayers, which may have important biological implications. Multilayers of DPPC and nucleotide-based copolymers could be transferred onto solid supports, in the form of Y-type Langmuir-Blodgett films, in which the molecular-level interactions led to lower energies in the vibrational spectra of the nucleotide-based copolymers. The successful deposition of solid films opens the way for devices to be produced which exploit the molecular recognition properties of the nucleotides.

Atmospheric Pressure Photoionization Tandem Mass Spectrometry for the Analysis and Characterization of Cholesteroloxidized Products

The fabrication of Langmuir-Blodgett (LB) films from lignins is reported for the first time. Lignins extracted from Pinus caribaea hondurensis and sugar cane bagasse are shown to form stable Langmuir monolayers on ultrapure water which can be transferred onto glass substrates in the form of Y-type LB films. The area per molecule increases linearly with the molecular weight of the bagasse lignins which were fractionated by GPC so that relatively monodisperse materials could be obtained. This contrasts with the results from the highly disperse Pinus lignins for which no clear trend in the change in area per molecule could be observed. Ellipsometric measurements indicated that the thickness of LB films from both types of lignin is 60 Å per deposited layer, the films possessing a large free volume. This clearly demonstrates that lignin molecules assume a three-dimensional arrangement even within a single layer.

Preparation of Ultrathin Silsesquioxane Nanofilms via Polymer Langmuir−Blodgett Films

This Article describes a unique approach to building silsesquioxane nanoassemblies based on the Langmuir−Blodgett (LB) technique. Poly(N-dodecylacrylamide-co-3-methacryloxypropyl-T8-heptatrifluoropropyl (or heptaphenylpropyl) POSS)s (p(DDA/SQ)s) were synthesized through free radical copolymerization using propyl methacrylate-substituted polyhedral oligomeric silsesquioxane (POSS) monomers containing seven nonreactive trifluoropropyl or phenyl groups (R7(Si8O12)(CH2CH2CH2OCOCH3C═CH2) (where R is either trifluoropropyl (SQF) or phenyl (SQPh)) and amphiphilic copolymers. The p(DDA/SQ)s formed stable monolayers at the air/water interface. The monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. The polymer LB films had a well-defined layer structure and a surface flatness (rms values < 1 nm in 1 μm2). The high heat-resistant properties of the p(DDA/SQ) LB films were demonstrated using UV−vis spectroscopic reflectometry and FT-IR. The refractive index and the th...

Redox-Active Cellulose Langmuir−Blodgett Films Containing β-Carotene as a Molecular Wire

Redox-active Langmuir-Blodgett (LB) films containing dihydrophytyl ferrocenoate (DFc) and beta-carotene (betaC) were fabricated by use of 6-O-dihydrophytylcellulose (DHPC) as a matrix. A mixture of DFc-DHPC formed a stable monolayer. Atomic force microscopy images revealed that the DFc molecules were dispersed uniformly throughout the surface in the ratio DFc:DHPC = 2:8 at 30 mN m-1. The DFc-DHPC monolayer was transferred successfully onto a substrate, yielding Y-type LB films. Cyclic voltammograms for the DFc-DHPC LB films on an indium tin oxide (ITO) electrode exhibited a well-defined surface wave. The voltammograms of the DFc-DHPC LB films exhibited 60-40% redox-active ferrocene moieties, whereas those of the DFc-DHPC-betaC LB films exhibited 90-70%. X-ray diffraction patterns indicated that the distance between layers was independent of betaC molecules incorporated into the LB films. Consequently, these results suggested that betaC can function as a molecular wire.

The dipole interaction model of the molecular aggregation in Y-type Langmuir-Blodgett film

Based on the classical electrostatic theory, the model of dipole-dipole interaction of rod-like amphiphilic molecules in Y-type Langmuir-Blodgett (LB) film is presented in the paper. The relations between the structure and spectral absorption peak of LB films were obtained by using this model. For Y-type films, the relationship of molecular aggregation state and the structure parameters, i.e. molecular separation distance a, separation d between two adjacent layers, molecular tilt angle θ, and layer number g, were studied using our model. Then we compared the similarities and differences of aggregation behavior between Y-type and Z-type films. The theoretical results agree well with experimental data.

Langmuir−Blodgett Films of a Novel Cellulose Derivative with Dihydrophytyl Group: The Ability to Anchor β-Carotene Molecules

A novel cellulose derivative, 6-O-dihydrophytylcellulose (DHPC), was first synthesized via a ring-opening polymerization and allowed to self-assemble onto an air-water interface. Langmuir-Blodgett (LB) films were characterized with atomic force microscope (AFM), UV-vis spectroscopy, and Fourier transform infrared spectroscopy. The surface pressure-area (pi-A) isotherms for DHPC and beta-carotene (betaC) mixture indicated strong interaction between these compounds to pack well. Thus, DHPC has the ability to anchor betaC in the monolayer. It was proved that a betaC-DHPC monolayer was transferred successfully onto a substrate, yielding Y-type LB films by UV spectroscopic analysis. The transmission and reflection-absorption IR spectra (RAS) indicated that the dihydrophytyl chains had almost trans-zigzag conformation and were oriented nearly perpendicular to the substrate. AFM section analysis revealed the thickness per layer to be 2.32 nm. Consequently, DHPC was found to be an appropriate matrix to fabricate the mixed LB films containing betaC.

Thermodynamic characteristics and Langmuir–Blodgett deposition behavior of mixed DPPA/DPPC monolayers at air/liquid interfaces

The role of dipalmitoylphosphatic acid (DPPA) as a transfer promoter to enhance the Langmuir–Blodgett (LB) deposition of a dipalmitoylphosphatidylcholine (DPPC) monolayer at air/liquid interfaces was investigated, and the effects of Ca 2+ ions in the subphase were discussed. The miscibility of the two components at air/liquid interfaces was evaluated by surface pressure–area per molecule isotherms, thermodynamic analysis, and by the direct observation of Brewster angle microscopy (BAM). Multilayer LB deposition behavior of the mixed DPPA/DPPC monolayers was then studied by transferring the monolayers onto hydrophilic glass plates at a surface pressure of 30 mN/m. The results showed that the two components, DPPA and DPPC, were miscible in a monolayer on both subphases of pure water and 0.2 mM CaCl 2 solution. However, an exception occurs between X DPPA = 0.2 and 0.5 at air/CaCl 2-solution interface, where a partially miscible monolayer with phase separation may occur. Negative deviations in the excess area analysis were found for the mixed monolayer system, indicating the existence of attractive interactions between DPPA and DPPC molecules in the monolayers. The monolayers were stable at the surface pressure of 30 mN/m for the following LB deposition as evaluated from the area relaxation behavior. It was found that the presence of Ca 2+ ions had a stabilization effect for DPPA-rich monolayers, probably due to the association of negatively charged DPPA molecules with Ca 2+ ions. Moreover, the Ca 2+ ions may enhance the adhesion of DPPA polar groups to a glass surface and the interactions between DPPA polar groups in the multilayer LB film structure. As a result, Y-type multilayer LB films containing DPPC could be fabricated from the mixed DPPA/DPPC monolayers with the presence of Ca 2+ ions.

Photoconductive Properties of Organic−Inorganic Hybrid Films of Layered Perovskite-Type Niobate

A hybrid film of layered niobate and an organic amphiphile was prepared by the Langmuir-Blodgett (LB) method. Trimethylammonium-exchanged perovskite-type niobates ((CH(3))(3)NHSr(2)Nb(3)O(10)) were exfoliative to form an aqueous suspension. A monolayer of octadecylamine was produced on such an aqueous dispersion as a template for a hybrid film. A hybrid film was transferred as a Y-type LB film onto a hydrophilic glass plate or an ITO substrate. The structure of a deposited film was investigated with X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic force microscopy (AFM) measurements, indicating a layer-by-layer structure with a single or double sheet of niobate as an inorganic composite. From the cyclic voltammogram on an ITO electrode modified with the Y-type 10 layered film, the lower edge of the conduction band of a niobate layer was determined to be - 0.6 V (vs Ag/AgCl). ac impedance and dc measurements were carried out on 1, 5, and 10-layered LB films (2 mm (electrode spacing) x 8 mm (width)) with aluminum electrodes. The freshly deposited samples behaved as an insulator under the illumination of 280 nm light (2.04 x 10(16) quanta s(-1)). Photoconductivities appeared, however, when they were preirradiated with a 150 W Xe lamp (ca. 2 x 10(18) quanta s(-1)) for 0.5-8.5 h. The process was denoted as photomodification. From the FT-IR and XRD results, it was deduced that the photomodification of LB films caused the decomposition of organic templates (octadecylammonium) accompanied by the collapse of layer-by-layer structures. dc analyses on the 5- and 10-layered films after photomodification also showed that they behaved as a photosemiconductor under UV light illumination.

Optical properties and aggregation of novel azo-dyes bearing an end-capped oligo(ethylene glycol) side chain in solution, solid state and Langmuir–Blodgett films

Optical properties and aggregation of two novel azo-dyes N-methyl- N-{4-[( E)-(4-nitrophenyl)diazenyl]phenyl}- N-(3,6,9-trioxadecas-1-yl)amine ( RED-PEGM-3) and N-methyl- N-{4-[( E)-(4-nitrophenyl)diazenyl] phenyl}- N-(3,6,9,12,15,18,21,24-octaoxapentaeicos-1-yl)amine ( RED-PEGM-8) were studied by UV–vis spectroscopy in solution, solid state and Langmuir–Blodgett films. The results were compared to those obtained for their precursor 1-amino-4′-nitroazobenzene (Disperse Orange 3, DO3) and 1- N-methylamino-4′-nitroazobenzene ( RED-H). Increasing the polarity of methanol:water mixtures gave rise to the formation of H-aggregates for all dyes. Similar aggregates were also detected in cast films. NOESY, 2D 1H NMR experiments carried out in aqueous solutions of RED-PEGM-8 revealed the formation of atypical antiparallel H-aggregates. Only RED-PEGM-3 gave traces of J-aggregates in the solid state. RED-PEGM-3 and RED-PEGM-8 readily form J-aggregates in Y-type Langmuir–Blodgett films.

Studies of Langmuir and Langmuir–Blodgett films of NLO-active amphiphilic 1,3-indanedione derivatives

We studied Langmuir and Langmuir–Blodgett (LB) films of several strong nonlinear optical (NLO) active amphiphilic derivatives of 1,3-indanedione-5,6-dicarboxylic acid. The surface pressure–area (π–A) isotherms at the air–water interface were investigated at different temperatures and pH values. Non-centrosymmetric Z-type LB films were deposited. UV–visible spectra indicated a uniform film transfer. The orientation of the molecular transition moments was calculated from the polarized UV–visible spectra. Packing within the LB films was observed by UV–visible absorption and fluorescence spectroscopy. The morphology of the LB films was examined by AFM and compared to ellipsometric measurements, and the nature of the films was studied by contact angle measurements. Significant second harmonic generation (SHG) by the LB films was observed. Alternate layer Y-type LB films of two different dyes were fabricated to achieve enhanced stability and SHG.

Mono- and multi-layer langmuir-blodgett films of maleimide polymers possessing nonlinear optical-active side chains

A copolymer P[OSA-MI] was synthesized by copolymerization of its corresponding monomers,N-phenyl maleimide (MI) and 2-octen-1-ylsuccinic anhydride (OSA). The polymer (poly[2-[1-(2,5-dioxo-1-phenylpyrrolidin-3-ylmethyl)heptyl]-succinic acid 4-(2-{ethyl-[4-(4-nitrophen-ylazo) phenyl]amino}ethyl) ester]) P[DR1MA-MI] was obtained from the reaction of P[OSA-MI] with 2-[4-(4-nitrophenylazo)-N-ethylphenylamino] ethanol (DR1). A stable monolayer of P[DR1MA-MI] was formed by spreading the solution of the polymer in chloroform. In Y-type Langmuir-Blodgett (LB) films prepared using this Langmuir-Blodgett method, the second harmonic waves generated from adjacent monolayers canceled each other out. In X- and Z-type LB films, the second harmonic intensity increased upon increasing the number of monolayers, but this increase was somewhat smaller than predicted by the square law. This phenomenon is due to defects or imperfect alignment of the dipoles in the LB film. The generation of second harmonic waves from Y-type LB films having an even number of monolayers supports this argument. The degree of imperfection seemed to increase as the number of layers increased. The second-order nonlinear optical properties of spin-cast films of these polymers were also measured. The largest second harmonic coefficient of the poled P[DR1MA-MI] film coated on a glass plate was 19 pm/V.

Macroscopic Alignment of Graphene Stacks by Langmuir−Blodgett Deposition of Amphiphilic Hexabenzocoronenes

We present structural studies of Langmuir (L) and Langmuir-Blodgett (LB) films of new amphiphilic hexa-peri-hexabenzocoronene (HBC) discotics, carrying five branched alkyl side chains and one polar group. The polar group is either a carboxylic acid moiety or an electron acceptor moiety (anthraquinone). Grazing-incidence X-ray diffraction (GIXD) and X-ray reflectivity, both utilizing synchrotron radiation, show that these amphiphilic HBCs form well-defined Langmuir monolayers at the air-water interface, with a pi-stacked columnar structure where the HBC cores are rotated around the surface normal and tilted relative to the water surface. The intercolumnar distance is 20 A. The HBCs are confined to a layer lying on top of the layer of polar groups that are in contact with the water subphase. Efficient transfer of the monolayer of the anthraquinone-substituted HBC derivative to hydrophobic quartz substrates by vertical dipping gave well-defined multilayer Y-type LB films. Polarized optical spectroscopy, GIXD, and X-ray reflectivity measurements show that the LB films consist of at least two phases. Heating the films results in an irreversible rearrangement to a single macroscopically aligned phase of hexagonally packed columns oriented along the dipping direction with disk planes perpendicular to the columnar axes and stacked in a cofacial manner. This phase transition is analogous to the reversible transition observed in the bulk material.

Preparation and characterization of Y 2O 3-doped CeO 2 ultrathin film made from Langmuir–Blodgett films

Ultrathin Y 2O 3-doped CeO 2 (YDC) ceramic films have been prepared using Langmuir–Blodgett (LB) films as precursors. β-diketonate complexes Ce(tmhd) 4 and Y(tmhd) 3 were chosen as the ‘surface ions’ which can combine with arachidic acid (AA) to form uniform mixed monolayer on pure water. Y-type LB films were fabricated by depositing the mixed monolayer with mixed ratio of Y(tmhd) 3/Ce(tmhd) 4/AA=1:7:16. The smooth and homogeneous YDC films were obtained through a combination of room temperature ultra-violet/ozone decomposition and annealing treatments. The X-ray diffraction, X-ray photoelectron spectroscopy and a.c. impedance spectra measurements demonstrate that the final films are single YDC phase with a fluorite cubic structure indeed and the components of the films can be accurately controlled through the whole process.

Langmuir–Blodgett films based on europium-substituted heteropolytungstate and their luminescence properties

Several new hybrid organic–inorganic Langmuir–Blodgett (LB) films containing europium-substituted heteropolytungstate Eu (XW 11O 39) 2 n− (X=Ge, Si, B) were successfully obtained using LB technique. When the heteropolytungstate anions are dissolved in the subphase, dimethyldioctadecylammonium bromide compression isotherms have been modified, which shows that the polyanions interact with the monolayer. Y-type LB films were obtained from the systems. Low-angle X-ray has shown that these LB films have well-defined lamella. The LB films were characterized by luminescence spectra and the characteristic luminescence behavior for europium-substituted heteropolytungstate complexes and their LB films were discussed. The results of excitation spectra indicate that the energy could be effectively transferred from ligands to the Eu 3+ ions in the LB films and the luminescence efficiency could be greatly increased. The results of luminescence spectra indicate that the formations of hybrid organic–inorganic LB films have a great effect on the luminescence of europium-substituted heteropolytungstate. The lifetime shortening was observed in LB films.

Organic/Inorganic Langmuir−Blodgett Films Based on Metal Phosphonates. 5. A Magnetic Manganese Phosphonate Film Including a Tetrathiafulvalene Amphiphile1

Mixed organic/inorganic Langmuir−Blodgett (LB) films have been prepared in which the polar network is a manganese phosphonate continuous lattice and the organic network contains a substituted tetrathiafulvalene amphiphile. The bis(phosphonic acid) amphiphile, 2,3-bis[(4‘-phosphonobutyl)thio]-6,7-bis(tetradecylthio)tetrathiafulvalene, 1, has been synthesized and deposited from an aqueous Mn2+ subphase to form Y-type LB films with stoichiometry Mn2(1)(H2O)2. Since the amphiphile is a bis(phosphonate), the inorganic network forms the Mn(O3PR)H2O structure known in other manganese phosphonate LB films and layered solids. The film becomes magnetic near 11.5 K when the manganese phosphonate network orders as a canted antiferromagnet. Attempts to subsequently oxidize the tetrathiafulvalene (TTF) network did not result in stable phases. Structural characterization was aided by the synthesis of a solid-state manganese bis(phosphonate) model compound, Mn2(2)(H2O)2, where 2 is the ligand 2,3-bis[(2‘-phosphonoethyl)thio]-6,7-bis(methylthio)tetrathiafulvalene.