Schaefer Films Research Articles

Growth of thiol-coated Au-nanoparticle Langmuir monolayers through a 2D-network of disk-like islands

Formation of 2D-networked structures of disk-like islands for ultrathin Langmuir–Schaefer (LS) films of thiol-coated Au-nanoparticles (DT-AuNPs) on H-passivated Si substrates is evidenced for the first time, by X-ray scattering data and AFM images.

Controlling surface adsorption to enhance the selectivity of porphyrin based gas sensors

This study reports an enhancement in the selectivity of the vapor sensing properties of free base porphyrin 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO) Langmuir–Schaefer (LS) films. These sensors respond by changing color upon adsorption of the analyte gas to the sensor surface. The enhanced selectivity is achieved by adding selective barrier layers of 4-tert-Butylcalix[4]arene, 4-tert-Butylcalix[6]arene and 4-tert-Butylcalix[8]arene embedded in PMMA (Poly(methyl methacrylate)) on top of the porphyrin sensor films to control the gaseous adsorption onto the sensor surface. The Langmuir properties of EHO, PMMA and calix[n]arene monolayers were investigated by surface pressure–area (Π–A) isotherms in order to determine the most efficient transfer pressure. Six layer EHO films were transferred onto glass and silicon substrates to investigate their optical and structural characteristics. The three different calix[n]arenes were embedded within PMMA layers to act as the selective barrier layers which were deposited on top of the six layer EHO films. The different calix[n]arene molecules vary in size and each was mixed with PMMA in specific ratios in order to control the selectivity of the resulting barrier layers. Spectroscopic Ellipsometry (SE) and Atomic Force Microscopy (AFM) measurements were carried out to analyze the structure of the porous barrier layers. It was found that the orientation of the calix[8]arene molecules was well controlled within the Langmuir layers such that molecular ring lies flat on the EHO layers when deposited. However, the calix[6]arene and calix[4]arene molecules were quite not so reliably oriented. The sensor films (with and without the addition of the different selective barrier layers) were exposed to various carboxylic acid vapors. More specifically, acetic acid, butyric acid and hexanoic acid were chosen due to their different molecular sizes. The uncovered EHO films were highly sensitive to all the carboxylic acids. The porosity of the barrier layers which influences their selectivity was investigated by changing the size of the acid molecules. Upon deposition of a barrier layer on top of EHO film the sensing response rate and magnitude were changed depending on both the barrier layer structure and molecular size of the analyte vapor. The optical sensing results show that by controlling the size of the pores in the barrier layer it can be used as a size selective layer which limits the diffusion of analyte molecules into the sensor and in extreme cases stopping the diffusion completely. Therefore the selectivity of this sensor system has been enhanced by adding a controllable barrier layer. The enhanced sensors have been used to differentiate between acetic, butyric and hexanoic acids.

Water-binding phospholipid nanodomains and phase-separated diacylglycerol nanodomains regulate enzyme reactions in lipid monolayers.

Phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) nanodomains covered with bound water as well as diacylglycerol 1-palmitoyl-2-oleoyl-sn-glycerol (POG) nanodomains separated from a lipid membrane were studied, using monolayer surfaces of POPC hydrolyzed by phospholipase C (PLC). The investigation was based on the analysis of compression isotherms and on atomic force microscope (AFM) observations of Langmuir-Blodgett (LB) films and Langmuir-Schaefer (LS) films. The results included reaction rate constants obtained by kinetic analysis of phosphocholine at surface pressures from 0.1 to 31 mN/m and determined by a luminol-enhanced chemiluminescence method. Monolayer elastic modulus values and fluorescence microscopic images confirmed that hydrolysis by PLC progressed in the intermediate monolayer between a liquid-expanded (L1) film and a liquid-condensed (L2) film at 2-17 mN/m. Furthermore, the intermediate film was confirmed to consist of L1 film and the POPC nanodomains in the L2 state are covered with bound water, conclusions based on the following AFM results: (1) nanodomains in POPC LS films were catalyzed by PLC, (2) POG nanodomains extended out from LB films of mixed POPC/POG 9/1 (mol/mol) monolayers, and (3) POPC LS films were covered with bound water, as indicated by cross-sectional analysis. At the optimal surface pressure of 10 mN/m, when POPC nanodomains (L2), with internal diameters of ∼75 nm, were hydrolyzed by PLC, they shrank down into pockets of the same size as those that appeared with POG. The resulting pocket sizes on LS films were in agreement with POG nanodomain sizes on LB films. This study demonstrated that PLC reacted with POPC nanodomains (L2) dispersed in L1/L2 mixed phase monolayers selectively and that POG nanodomains were phase-separated from the monolayer as hydrolysis proceeded.

Surface plasmon coupled metal enhanced spectral and charge transport properties of poly(3,3'''-dialkylquarterthiophene) Langmuir Schaefer films.

The coupling of organic molecule excitons with metal nano-structure surface plasmons can improve the performance of optoelectronic devices. This paper presents the effect of localized silver metal surface plasmons on spectral as well as charge transport properties of ordered molecular Langmuir Schaefer (LS) films of a fluorescent conducting multifunctional organic polymer: poly (3,3'''-dialkylquarterthiophene) [PQT-12]. The stability and thickness of the PQT-12 LS film were studied by the pressure vs. area isotherm curve. Atomic force microscopy images indicate the formation of a smooth ordered polymer thin LS film of PQT-12 over silver nanostructure island films [SNIF] (∼40 to 50 nm in size). Raman, electronic absorption and fluorescence spectral measurements of the PQT-12 LS film, near SNIF i.e. the near field, show a plasmon coupled enhancement of ∼13 fold in the intensity of Raman bands along with a two-fold enhancement in the absorption band (531 nm) and a six-fold enhancement in the fluorescence band (665 nm) coupled with a decrease in fluorescence decay time with improved photostability as compared to an identical control sample containing no SNIF i.e. the far field condition. These results indicate the formation of a plasmon coupled unified fluorophore system due to adsorption of the PQT-12 LS film over SNIF. The effect of plasmonic coupling is also studied by applying an electric field in sandwiched structures of Al/PQT-12 LS/SNIF/ITO with respect to Al/PQT-12 LS/ITO. Nearly three orders of magnitude enhancement in the current density (J-V plot) of the PQT-12 LS film is observed in the presence of SNIF, which further increases, on illuminating the film by green laser light [532 nm], while the fluorescence intensity and decay time decrease. X-ray photoelectron spectroscopic measurements of SNIF also show a red shift in 3d3/2 and 3d5/2 transitions of silver in the PQT-12 coated LS film, which indicates partial charge transfer from the PQT-12 polymer backbone to SNIF and causes an enhancement in conductivity. This again supports the formation of a field controlled radiating plasmon coupled fluorophore unified system. These findings show greater potential in developing a voltage controlled high photon flux electroluminescent material for multifarious applications.

Characterization of Langmuir monolayer, Langmuir–Blodgett and Langmuir–Schaefer films formed by POSS compounds

The properties of Langmuir monolayers and Langmuir–Blodgett as well as Langmuir–Schaefer films formed by two open-cage polyhedral oligomeric silsesquioxanes (POSS): 1,3,5,7,9,11,14-hepta-isooctyltricyclo [7.3.3.15,11] heptasiloxane-endo-3,7,14-triol (TSiO-POSS) and 1,3,5,7,9,11-octaisobutyltetracyclo [7.3.3.15,11] octasiloxane-endo-3,7-diol (DSiB-POSS) were studied. Both compounds were shown to form stable monolayers at the air/water interface. The morphology of the monolayers was visualized with a Brewster Angle Microscopy (BAM). The results obtained indicated that TSiO-POSS molecules formed dimers whereas in the case of DSiB-POSS was found the network structure, which was seen on the water/air interface as well as on L-S and L-B thin films. The difference in the interfacial behavior of POSS considered results from alkyl chains length and number of hydroxyl groups in the POSS molecule. The formation of network structure and presence of POSS dimers after transfer of the films on the solid substrates were reported.

Effect of molecular architectures in photoinduced birefringence in films of azo-modified diblock copolymers

Langmuir films of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with an azo dye, 4-[4-(phenylazo)-1-naphthylazo]phenol (Disperse Orange 13, DO13), hydrogen-bonded to the pyridine group of P4VP blocks were investigated. The surface pressure isotherms were considerably different for the copolymer dissolved in a nonselective (chloroform) and selective (toluene) solvents. The Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) films produced with PS-b-P4VP(DO13) copolymers displayed higher optically induced birefringence than the cast films owing to their nanostructured nature. The photoinduced birefringence properties were particularly enhanced when toluene was used owing to the confinement of azo chromophores in micelles consisting of a P4VP core and a PS corona.

Langmuir and Langmuir–Schaefer Films of Poly(3-hexylthiophene) with Gold Nanoparticles and Gold Nanoparticles Capped with 1-Octadecanethiol

This paper reports on the production of Langmuir films of regioregular poly(3-hexylthiophene) (P3HT) and their characterization by surface pressure isotherms and UV–vis in situ spectroscopy aiming at the best spreading conditions. Hybrid films containing the polymer and gold nanoparticles were obtained through the use of the optimized parameters for neat P3HT. Two types of hybrid films with P3HT and gold nanoparticles were studied. In the first type, gold nanoparticles in an aqueous solution were used in a subphase of a Langmuir trough and the polymer spread on the air/water interface. In the second type, 1-octadecanethiol capped gold nanoparticles (AuNpOctathiol) were used in a mixture with P3HT in chloroform and spread on the air–water interface. The Langmuir films were transferred to several solid substrates by the Langmuir–Schaefer (LS) method. The surface morphology was characterized by Scanning Electron Microscopy with Field Emission Guns (SEM-FEG), and the presence of gold nanoparticles in the films was confirmed. The growth of the layers in the films was monitored by transmission UV–vis spectroscopy, and the existence of optical anisotropy was investigated by polarized UV–vis spectroscopy. The results imply that the polymer backbone adopts a preferential orientation during the compression, which has a strong component parallel to the trough barrier, and is influenced by the presence of the nanoparticles in the films. The photostability of the films was studied by their exposition to a white light, and the hybrid films formed with P3HT and AuNpOctathiol showed an increase in the photostability, in comparison to the neat P3HT. Such an increase indicates that somehow the AuNpOctathiol molecules provide some protection against the photodegradation of P3HT.

Langmuir–Schaefer Films for Aligned Carbon Nanotubes Functionalized with a Conjugate Polymer and Photoelectrochemical Response Enhancement

Single-walled carbon nanotubes (SWCNTs) were suspended in 1,2-dichloroethane by noncovalent functionalization with a low-band-gap conjugated polymer 1 alternating dialkoxyphenylene-bisthiophene units with benzo[c][2,1,3]thiadiazole monomeric units. The suspended 1/SWCNT blend was transferred onto different solid substrates by the Langmuir-Schaefer deposition method, resulting in films with a high percentage of aligned nanotubes. Photoelectrochemical characterization of 1/SWCNT thin films on indium-tin oxide showed the benefits of SWCNT alignment for photoconversion efficiency.

Molecular orientation of Ru(II) complexes introduced in hybrid Langmuir–Schaefer films of clay nanosheets and alkylammonium cations

Ternary component hybrid films of amphiphilic alkylammonium cations, clay nanosheets, and ruthenium(II) complex cations were prepared by the modified Langmuir–Schaefer method. When a solution of the amphiphilic ammonium salt (octadecylammonium chloride, ODAH+Cl−) was spread at an air–clay dispersion interface, the clay nanosheets in the dispersion were adsorbed on the floating molecular film of ODAH+ by the electrostatic interaction. Then the floating film of ODAH+ and the clay was deposited on a glass plate and immersed in an aqueous solution of [RuL3]Cl2 (L=2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (dmphen), and 4,7-diphenyl-1,10-phenanthroline (dpp)) to form a ternary component hybrid monolayer. By repeating these procedures, a hybrid multilayer was fabricated. Characterization of the hybrid multilayers was carried out by electronic and IR spectral measurements and X-ray diffraction (XRD) method. Areas per [RuL3]2+ estimated from the analysis of the electronic spectra suggested that the Ru(II) complex cations interacted with each other through hydrophobic interaction. IR and XRD data indicated disordered alkylchains of ODAH+ which would occupy spaces between the [RuL3]2+ cations in the film. The tilt angles of 3-fold axes of [RuL3]2+ were determined to be 32–35° by analyzing electronic spectra measured with p- and s-polarized beams. An orientation model of the [RuL3]2+ cations in the film was proposed, in which substitution groups at 4- or 5-positions of 1,10-phenanthroline ligand were in contact with the clay nanosheet layers. It was likely that the sizes of the ligands and the interaction between the ligands affected the structure of the hybrid film.

Porphyrin–polyoxometalate hybrids connected via a Tris-alkoxo linker for the generation of photocurrent

Films on ITO of [N(C4H9)4]5H[P2V3W15O59{(OCH2)3CNHCO(ZnTPP)}] (ZnTPP=zinc(II)-tetraphenylporphyrin) were obtained by the Langmuir–Schaefer inverted transfer method.The films were characterized by UV–vis absorption spectroscopy, XPS, AFM, and electrochemistry. In addition, the photovoltaic performances of the Langmuir–Schaefer films were investigated by photocurrent transient measurements, which show significant photocurrent response.

In Situ Coordination and Supramolecular Chirality of Some Achiral Benzothiazole-derived Schiff Bases Fabricated at Air/Water Interface

Abstract A series of benzothiazole-derived Schiff bases was synthesized, and its interfacial behavior was investigated. Although these Schiff bases with no alkyl chains could not be spread on water surface, addition of metal ions such as Ag(I) or Cu(II) in the subphases caused an in situ coordination and led to the film formation. It was interesting to find that some of the Langmuir–Schaefer (LS) films of the Cu(II) complexes showed CD signals, although the Schiff bases were achiral. It was suggested that the stereoregular stacking of the coordinated complexes in a helical sense was responsible for the supramolecular chirality.

Biosensing invertase-based Langmuir–Schaefer films: Preparation and characteristic

The formation of hybrid films of the industrially important enzyme invertase and fatty lipids under enzyme-friendly conditions is described. The approach involves a simple physical adsorption protocol wherein invertase adsorbs into the preformed cationic phospholipid–octadecylamine Langmuir–Schaefer (LS) film. Immobilization of invertase onto the film is highly pH-dependent, underlining the role of attractive electrostatic interactions between the enzyme and the lipid layer. The stability of the enzyme in the lipid matrix was confirmed by biocatalytic activity measurements. Withal, the sensor sensitization was achieved by an amphiphilic conducting structure –N-hexadecyl-2,8-bis(thianthrene)phenothiazine admixed into the film. The interlaced compound was expected to facilitate the electron transfer as well as to enhance the sensor sensitivity. The control of molecular architecture and choice of a suitable phospholipid–octadecylamine matrix allows invertase-containing Langmuir–Schaefer films to be used in sucrose sensing devices.

Optical, morphological and structural characterization of Langmuir–Schaefer films of a functionalized copper phthalocyanine

Langmuir–Schaefer (LS) films of copper(II) tetrakis-(isoprpoxy-carbonyl)-phthalocyanine (TiPCuPc) have been deposited onto various solid supports. Its floating film have been characterized at the air–water interface by means of Brewster Angle Microscopy and Langmuir curves. Vibrational modes of multilayer transferred LS film have been studied by Raman spectroscopy and the optical parameters (refractive index n and extinction coefficient k) have been determined in the visible range of the electromagnetic spectrum. Linearly polarized light absorbance measurements have been performed at room temperature in the 400–800 nm spectral range and the average orientation of the phthalocyanine rings have been estimated. Transmission electron microscopy has been also used to characterize the morphological properties of the LS film and a close packed arrangement of the deposited molecules has been observed.

Nanostructuring polymers, colloids, and nanomaterials at the air–water interface through Langmuir and Langmuir–Blodgett techniques

Nanostructuring macromolecules and nanomaterials at the air–water interface through Langmuir monolayers, Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) films has been effectively used to investigate surface chemical/physical properties and achieve well-controlled surface morphologies. In this article, we review research progress and approaches in utilizing specific amphiphilic polymers, π-conjugated polymers, dendrons/dendrimers, metal/semiconductor nanoparticles, and colloidal spheres. Well-designed polymers, colloids, and nanomaterials enable structure–property correlation and observation of new phenomena not previously observed in bulk materials.

Molecular organization and effective energy transfer in iridium metallosurfactant–porphyrin assemblies embedded in Langmuir–Schaefer films

Mixed Langmuir monolayers and Langmuir-Schaefer (LS) films containing the cationic metallosurfactant bis(2-phenylpyridine)(4,4'-diheptadecyl-2,2'-bipyridine)-iridium(III) chloride (Ir-complex) and the anionic tetrakis(4-sulfonatophenyl)porphyrin (TSPP) in 4:1 molar ratio have been successfully prepared by the co-spreading method at the air-water interface. The presence of both luminescent species at the interface, as well as the organization of the TSPP underneath the Ir-complex matrix in Langmuir and LS films, is inferred by surface techniques such as π-A isotherms, reflection spectroscopy, Brewster angle microscopy (BAM) and UV-visible absorption spectroscopy. A red-shift in the absorption band of the porphyrin under the compression of the mixed monolayer suggests the J-aggregation of the TSPP under the Ir-complex matrix. To date, this is the first report of Langmuir and/or LS films containing these two types of species together. Furthermore, the intermolecular energy transfer between Ir-complex and TSPP molecules in solution and in transferred mixed films is investigated through steady-state fluorescence and lifetime measurements. These results indicate that effective intermolecular energy transfer occurs from the Ir-complex to the TSPP molecules in LS films. The influence of the spatial proximity of donor and acceptor molecules has been studied by the insertion of lipid interlayers among them.

Langmuir–Schaefer films of a polyaniline–gold nanoparticle composite material for applications in organic memristive devices

Langmuir–Shaefer films of a polyaniline–gold nanoparticle composite were fabricated and characterized. The thickness of each deposited monolayer, determined with AFM, was found to be about 0.8 nm. The film morphology was studied by SEM, revealing the presence of embedded spherical-shaped gold nanoparticles of about 5–10 nm in diameter. The fabricated films were used as the active channel of the organic memristor. Its electric characterisation has revealed new phenomena, such as an increased working voltage range and sigmoidal voltage current characteristics that were connected to the charge trapping.

Inverse Langmuir–Schaefer films of bent-core molecules

Mesostructures in inversed Langmuir–Schaefer films of each of two contrasting bent-core molecules are explored via atomic force microscopy. One of the molecules forms Langmuir films that are optically isotropic and the other those that are optically anisotropic. Both show suboptical mesostructures in the 100 nm range, in spite of appearing optically uniform. The anisotropic films are effective in aligning nematic bent-core samples, but not rod-like liquid crystals such as 5CB.

Active Langmuir–Schaefer films of tyrosinase—Characteristic

The structure and biosensor characteristic of complex between phenoloxidase (tyrosinase) and phoshpholipid thin ordered layer were investigated. The advantageous of immobilization method based on Langmuir–Schaefer (LS) film as a matrix has been developed for characterization of sensing protein layers effect. Tyrosinase from Agaricus bisporus molecules were densely adsorbed onto Langmuir monolayer surface and then deposited on solid support which can be used for phenolic compounds determination. The enzyme was immobilized by adsorption process. Phenoloxidase was adsorbed on monolayer built of 1,2-dipalmitoyl- S,N-glicero-3-phosphocholine (DPGPC). The sensor sensitization was achieved by an amphiphilic conducting structure – N-hexadecyl-3,6-bis(thianthrene)carbazole (HBTC) admixed into the film. The interlaced compound was expected to facilitate the electron transfer as well enhancing the sensor sensitivity. Considering the fact, that immobilization strategy showed high efficiency, obtained results suggest that our method for tyrosinase immobilization has a great potential of enabling high throughput fabrication of bioelectronics’ devices.

Morphology and photoconductivity of poly- N-vinylcarbazole-cellulose triacetate Langmuir–Schaefer films

Cellulose triacetate (CTA) was doped with poly( N-vinylcarbazole) (PVK) via the oxidative polymerization of N-vinylcarbazole with ferric chloride to form polymer blends. Langmuir–Schaefer (LS) films of the polymer blends were fabricated. The morphology of the cellulose triacetate-poly( N-vinylcarbazole) (PC) blends were analyzed using transmission electron microscopy. The pressure–area isotherm of PC blends revealed the possibility of compact monolayer formation at air–water interface. The voltammetric investigation of PC blends showed an appreciable electrochemical behavior. The photoinduced charge transfer across a donor/acceptor hybrid interface provided an effective method to study the photoelectrochemical properties of the PC polymer films.

Characterization and magnetic properties of conducting poly( N-vinylcarbazole)-capped magnetite nanocomposite Langmuir–Schaefer films

Functionalized poly( N-vinylcarbazole) (PVK) has been synthesized by an oxidative polymerization with capped magnetite nanoparticles (CMPs, 10, 20, and 30%) for the preparation of conducting polymer composites that possess both electrical and magnetic properties. Spectroscopic studies reveal the successful functionalization of the nanoparticles into the PVK matrix. I– V characteristics of the composite films show an increase in the conductivity of the PVK film due to the presence of CMPs. The magnetization data exhibit an appreciable hysteresis loop at room temperature. The composite samples reveal an ordered semi-conducting behavior.