Langmuir-Blodgett Film Formation Research Articles

Above room temperature spin crossover in mononuclear iron(II) complexes featuring pyridyl-benzimidazole bidentate ligands adorned with aliphatic chains.

Two bidentate ligands (L1 = 1-pentyl-2-(pyridin-2-yl)-1H-benzimidazole and L2 = 1-heptyl-2-(pyridin-2-yl)-1H-benzimidazole) were employed for the synthesis of five mononuclear Fe(II) coordination compounds 1-5 containing perchlorate, tetrafluoroborate and triflate counterions. Single-crystal X-ray diffraction analysis confirmed the expected molecular structures of all the reported compounds, revealing a moderately distorted octahedral geometry of {FeN6} coordination chromophores. All five compounds exhibit thermal spin crossover with T1/2 temperatures allocated above 400 K. The theoretical calculations supported the experimental magnetic investigation and helped to explain the electronic structures of the reported complexes with respect to the occurrence of thermal spin state switching. In addition, compound 4 was employed for the preparation of Langmuir-Blodgett films and fabrication of molecular films using the method of spontaneous evaporation of the subphase. While the formation of Langmuir-Blodgett films was unsuccessful due to the instability of the compound at the water/air interface, the latter technique allowed the formation of molecular films of 4 with well-defined thickness and homogeneity.

Formation behavior of monolayers on the water surface of water-soluble thermoplastic and insoluble-thermosetting copolymers with hyperbranched units containing s-benzenetricarbamide cores

The formation and structure of Langmuir monolayers and Langmuir-Blodgett films were studied using water-soluble polymers, which have difficulty forming monolayers on the water surface, and polymers that are insoluble in all solvents. The network copolymers consisting of hyperbranched units with an s-benzenetricarbamide core used in this study can be freely controlled by azidation/non-azidation of both ends of the hard segment. The water-soluble copolymer, which exhibits the properties of a thermoplastic resin, can form a monolayer when spread on the water surface at a low temperature at which the solubility decreases. Even when the subphase temperature increased, no significant change in the monolayer behavior of the thermoplastic copolymer was observed. This behavior was attributed to the formation of an insoluble single-particle layer with hydrophilic groups facing inward on the water surface. The insoluble copolymer, which exhibits thermosetting properties, forms a tablet that floats on the water surface for an extended period. The surface pressure-time isotherms showed the formation of a monolayer from the tablet over time, and it was possible to measure the surface pressure-area isotherms by two-dimensional compression after a certain period of time.

Probing the effect of nitro-substituents in the modulation of LUMO energies for directional electron transport through 4d6 ruthenium(II)-based metallosurfactants.

Electron-withdrawing nitro-substituents were installed onto terpyridine- and phenanthroline-based metallosurfactants with 4d6 ruthenium(II), which were deposited as Langmuir-Blodgett monolayers aiming to study the feasibility of charge transport in Au|LB|Au junctions. The nitro groups are intended to modulate the energy of the frontier molecular orbitals to near to, or match that of Fermi levels in the gold electrodes. A series of heteroleptic metallosurfactants [RuII(C18OPh-terpy)(X-terpy)](PF6)2 and [RuII(C18OPh-terpy)(X-phen)Cl]PF6 were synthesized, where C18OPh-terpy is the 4'-[4-(octadecyloxy)phenyl]-2,2':6',2''-terpyridine amphiphile common to all species, X-terpy is a terpyridine with-H (1) or-phenyl-NO2 (2) and X-phen is a phenanthroline with-H (3) or-NO2 (4) groups. These metallosurfactants were characterized by experimental and computational methods, and the presence of nitro groups affect more affordable reductions at less negative potentials, as well as slightly more positive oxidations, these changes are less pronounced in species 2 than in 4. Species 1 and 2 showed limited Pockels-Langmuir and Langmuir-Blodgett film formation with lower collapse pressure of 27 mN m-1. In contrast, metallosurfactants 3 and 4 showed enhanced hydrophilicity indicated by higher collapse pressures of ca. 36 mN m-1. The LB monolayers of 3 and 4 were deposited on gold electrodes to form Au|LB|Au junctions and electron transport was measured as I/V curves. The NO2-bearing species 4 showed asymmetric curves associated with directional electron transport with amplitudes up to -2.0 nA and rectification ratios from 5 to 26 between -1 to +1 V and from 3 to 14 between -3 to +3 V.

Langmuir-Blodgett Graphene-Based Films for Algal Biophotovoltaic Fuel Cells.

The prevalence of photosynthesis, as the major natural solar energy transduction mechanism or biophotovoltaics (BPV), has always intrigued mankind. Over the last decades, we have learned to extract this renewable energy through continuously improving solid-state semiconductive devices, such as the photovoltaic solar cell. Direct utilization of plant-based BPVs has, however, been almost impracticable so far. Nevertheless, the electrochemical platform of fuel cells (FCs) relying on redox potentials of algae suspensions or biofilms on functionalized anode materials has in recent years increasingly been demonstrated to produce clean or carbon-negative electrical power generators. Interestingly, these algal BPVs offer unparalleled advantages, including carbon sequestration, bioremediation and biomass harvesting, while producing electricity. The development of high performance and durable BPVs is dependent on upgraded anode materials with electrochemically dynamic nanostructures. However, the current challenges in the optimization of anode materials remain significant barriers towards the development of commercially viable technology. In this context, two-dimensional (2D) graphene-based carbonaceous material has widely been exploited in such FCs due to its flexible surface functionalization properties. Attempts to economically improve power outputs have, however, been futile owing to molecular scale disorders that limit efficient charge coupling for maximum power generation within the anodic films. Recently, Langmuir–Blodgett (LB) film has been substantiated as an efficacious film-forming technique to tackle the above limitations of algal BPVs; however, the aforesaid technology remains vastly untapped in BPVs. An in-depth electromechanistic view of the fabrication of LB films and their electron transference mechanisms is of huge significance for the scalability of BPVs. However, an inclusive review of LB films applicable to BPVs has yet to be undertaken, prohibiting futuristic applications. Consequently, we report an inclusive description of a contextual outline, functional principles, the LB film-formation mechanism, recent endeavors in developing LB films and acute encounters with prevailing BPV anode materials. Furthermore, the research and scale-up challenges relating to LB film-integrated BPVs are presented along with innovative perceptions of how to improve their practicability in scale-up processes.

Construction of Multifunctional and Adjustable Langmuir-Blodgett Composite Films Containing Black Phosphorus with High Stability for Optically Electrical Applications.

Fabrication of composite thin-film materials based on black phosphorus (BP) will greatly broaden the applications of BP in various areas. However, it is still a challenge to prepare a BP-based composite film with good stability and controllable structure. In this work, a series of BP-based composite Langmuir-Blodgett (LB) films are prepared by the self-assembly of polyethyleneimine (PEI)-modified BP nanosheets (BPNSs) (BPNS-PEI) and dye molecules. The presence of PEI greatly improves the stability of BPNSs. As for BPNS-PEI and dye molecules, the electrostatic interactions or π-π stacking interactions ensure the formation of stable composite LB films. Due to the protonation and deprotonation of amino groups, the synthesized BPNS-PEI/dye composite films show a sensitive response to acid and alkali gases, which shows wide application prospects as a highly sensitive gas sensor. Furthermore, surface-enhanced Raman scattering (SERS) proves that the prepared LB films exhibit good reproducibility and obvious Raman enhancement effect on rhodamine 6G molecules. In addition, due to the high carrier transfer rate of the obtained composite films, they possess enhanced photocurrent generation performance than pure BPNS-PEI and pure dye films. The current work demonstrates an effective method for preparing the ordered self-assembled BP-based composite LB films with good SERS and photoelectric conversion performance.

Coating of Conducting and Insulating Threads with Porous MOF Particles through Langmuir-Blodgett Technique.

The Langmuir-Blodgett (LB) method is a well-known deposition technique for the fabrication of ordered monolayer and multilayer thin films of nanomaterials onto different substrates that plays a critical role in the development of functional devices for various applications. This paper describes detailed studies about the best coating configuration for nanoparticles of a porous metal-organic framework (MOF) onto both insulating or conductive threads and nylon fiber. We design and fabricate customized polymethylmethacrylate sheets (PMMA) holders to deposit MOF layers onto the threads or fiber using the LB technique. Two different orientations, namely, horizontal and vertical, are used to deposit MIL-96(Al) monolayer films onto five different types of threads and nylon fiber. These studies show that LB film formation strongly depends on deposition orientation and the type of threads or fiber. Among all the samples tested, cotton thread and nylon fiber with vertical deposition show more homogenous monolayer coverage. In the case of conductive threads, the MOF particles tend to aggregate between the conductive thread’s fibers instead of forming a continuous monolayer coating. Our results show a significant contribution in terms of MOF monolayer deposition onto single fiber and threads that will contribute to the fabrication of single fiber or thread-based devices in the future.

Langmuir, Raman, and electrical properties comparison of calixarene and calixarene-rGO using Langmuir Blodgett (LB) technique

A layered composites of calix[4]arene, namely, THC4-rGO, was produced from calix[4]arene-25,26,27,28-tetrol (THC4) and reduced graphene oxide (rGO) using the Langmuir–Blodgett (LB) technique. THC4 and rGO were prepared in a solution form first, then by using the LB technique to form LB films which were then deposited onto a quartz surface for Raman and electrical study. Langmuir property such as surface pressure-area (Π-A) isotherms of THC4 and rGO were used to study the intermolecular interactions at air–water interface. Raman spectroscopy was used to observe the crystallinity of the composites. The electrical properties by using four-point probe, i.e., I–V curves, resistivity, and conductivities of the rGO and THC4-rGO were analyzed to illustrate the enhanced properties. The results from this study can be utilized for the potential application of electronic sensors using calix[4]arene.

Oligomeric silsesquioxanes containing dye Rhodamine B in an organic shell

A method for the synthesis of amphiphilic reactive oligomeric silsesquioxanes (OSS) with fragments of Rhodamine B fluorescent dye and hydroxyl groups in organic shell (OSS-Rh) by the reaction between carboxyl groups of the dye and epoxy groups of the mixture of oligomeric silsesquioxanes (OSS-Ep) was developed. The structure of the synthesized substance was characterized by the methods of IR and 1H NMR spectroscopy.
 The UV-spectrum of the OSS-Rh compound in dimethylformamide (DMF) solution was characterized by absorption bands of both the colored zwitterion (562 nm and 350 nm) and the colorless lactone (318 nm) forms of Rhodamine B. The absorption band at 562 nm in the spectrum of OSS-Rh in DMF solution was more intense than the analogous band in the spectrum of the original Rhodamine B. Therefore, the attachment of Rhodamine B to the silsesquioxane core of an oligomeric silsesquioxanes mixture does not have a significant effect on the position of the absorption maxima in UV-spectrum and prevents dye’s fragments from converting to the colorless lactone form.
 In the fluorescence spectra of both Rhodamine B and OSS-Rh, obtained using ethyl alcohol as a solvent, a peak is observed at λmax = 570 nm (λex = 500 nm). In the fluorescence spectrum of OSS-Rh obtained in DMF, a fluorescence peak is observed at λmax = 586 nm (λex = 520 nm). Consequently, the replacement of ethanol by DMF is accompanied by a bathochromic shift of the fluorescence peak of OSS-Rh. In the fluorescence spectrum of Rhodamine B at the same conditions, the peak of fluorescence is absent because of transition of the dye to the lactone form. The compounds obtained can be used in formation of functional Langmuir-Blodgett films as well as in obtaining polymer nanocomposites by covalent bonding.

High-Density and Monolayer-Level Integration of π-Conjugated Units: Amphiphilic Carbazole Homopolymer Langmuir-Blodgett Films.

Precise integration of π-conjugated units is a key issue to achieve molecular (nano) electronic devices based on organic semiconductor materials. We specifically examine the Langmuir-Blodgett technique, which allows high-density integration of π-conjugated units. In this study, we designed a carbazole containing acrylamide-based homopolymer [poly(9-ethyl-3-carbazolyl acrylamide) (pCzAA)], in which the π-conjugated unit is connected with a hydrophilic amide unit directly as a side chain. Its Langmuir-Blodgett film formation properties were investigated. The pCzAA polymer took a stable monolayer formation in the presence of a small amount (ca. 10 mol %) of poly( N-dodecylacrylamide) (pDDA). Compared with amphiphilic carbazole-containing copolymers described in earlier reports, the direct connection of π-conjugated units through amide bonding enables the Cz content in monolayers to exceed that of the copolymer monolayers (ca. 30 mol %) dramatically. pCzAA:pDDA takes highly ordered layer structures toward the out-of-plane direction, although no structural order is formed in the in-plane direction. This method is a practical means to develop low-dimensional and high-density integration of π-conjugated units for molecular electronics.

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.

Synthesis and Porous SiO2 Nanofilm Formation of the Silsesquioxane-Containing Amphiphilic Block Copolymer.

We describe the synthesis, Langmuir-Blodgett (LB) film formation, and photo-oxidation of an organic-inorganic hybrid block copolymer consisting of N-dodecyl acrylamide (DDA) and silsesquioxane (SQ) comonomers [p(DDA/SQ26)- b-pDDA]. The copolymer was synthesized by reversible addition fragmentation chain transfer polymerization of DDA and SQ. Higher monolayer stability at the air-water interface was confirmed for p(DDA/SQ26)- b-pDDA. The p(DDA/SQ26)- b-pDDA monolayer was deposited onto solid substrates with a monolayer thickness of 2.3 nm. The photo-oxidized SiO2 nanofilm revealed its porous structure, which reflects phase-separated structures of p(DDA/SQ26)- b-pDDA, as confirmed using atomic force microscopy, quartz crystal microbalance, and cyclic voltammetry measurements. These results demonstrate that this preparation method using photo-oxidation of the organic-inorganic hybrid block copolymer LB film is promising for manipulating pore formations of inorganic oxide nanofilms.

Formation and characterization of Langmuir and Langmuir-Blodgett films of Newkome-type dendrons in presence and absence of a therapeutic compound, for the development of surface mediated drug delivery systems

Organic macromolecules with dendrimeric architectures are polymeric materials potentially useful as nanocarriers for therapeutic drugs. In this work, we evaluate a series of Newkome-type dendrons in Langmuir and Langmuir-Blodgett films as platforms capable of interacting with a potential antitumoral agent. The nanocomposite is proposed as model for the development of surface mediated drug delivery systems. We were successful in the formation and characterization of pure (dendrons) and composite (drug-dendron) stable and reproducible monolayers, and their transfer to solid substrates. A detailed study of topographic characteristics of the generated surfaces by atomic force microscopy was conducted. Furthermore, we probed dendron monolayer films as anchorage surfaces for mammalian cells. Normal cell attachment and proliferation on the surfaces were observed. No evident cytotoxic effects were detected, demonstrating the adequate biocompatibility of the surfaces.

Nanostructured LB films developed from poly(p-acryloylaminophenylmethylphosphonic) acid

ABSTRACTIn this paper, the formation of Langmuir-Blodgett films of poly(p-acryloylaminophenylmethylphosphonic) acid polymers, with general formula (C10H12NPO4)n are reported. The Langmuir-Blodgett (LB) technique was used for building ordered nanostructures in molecular assemblies of these polymers, which were able to form stable films. At the air-water interface, these polymers (with low and high molecular weight) formed Langmuir (L) monolayers, which were characterized by surface pressure versus molecular area (π-A) isotherms and Brewster´s Angle Microscopy (BAM). Using the LB method, molecular mono and multilayer films of these polymers were prepared and transferred onto glass substrates forming Z-type multilayers, with a transfer ratio close to unity. These LB films were characterized by Atomic Force Microscopy (AFM).

Single Gold Atom Containing Oligo(phenylene)ethynylene: Assembly into LB Films and Electrical Characterization

Monomolecular films of an oligo(phenylene)ethynylene, OPE, derivative [2-isocyano-1,3-dimethylbenzene][4-(4′-aminophenylethynyl)phenylethynyl]gold, 1, containing a gold atom in the molecule backbone have been prepared by the Langmuir–Blodgett (LB) method in order to study how the electrical properties can be modulated in monolayers of OPEs by incorporation of a gold center in their structures. UV–vis reflection spectra of Langmuir monolayers of 1 at the air–water interface reveal strong aurophilic interactions between neighboring molecules that increase upon compression. Monolayer Langmuir–Blodgett (LB) films were readily fabricated by the transfer of Langmuir films of 1 onto solid substrates. Quartz crystal microbalance (QCM) experiments conclusively demonstrate formation of monolayer LB films with a high surface coverage. The morphology of these films was analyzed by atomic force microscopy (AFM), revealing formation of homogeneous layers with an optimum surface pressure of transference of 6 mN·m–1. Fil...

Equilibrium spreading pressure and Langmuir–Blodgett film formation of omega-substituted palmitic acids

Langmuir–Blodgett isotherms and equilibrium spreading pressures were measured for compounds of the series X–(CH2)15COOH, X=CH3, SH, OH, F, Cl, Br. Only the CH3 and F terminated compounds formed monolayers with sufficient stability for accurate isotherm measurement, film transfer and X-ray photoelectron spectroscopic analysis. The presence of the terminal heteroatom substituents significantly diminished the stability of the L–B film and depressed the equilibrium spreading pressures (20°C) from 15.4mN/m for the CH3 terminated compound to a range of 0.95 to 0.08mN/m for the other members of the series. These characteristics are attributed to the monolayer film being in a metastable state and the dipole moment of the heteroatom terminal group increasing the monolayer film kinetic instability by facilitating the formation of three-dimensional structures.

Near Infrared (NIR) Lanthanide Emissive Langmuir–Blodgett Monolayers Formed Using Nd(III) Directed Self-Assembly Synthesis of Chiral Amphiphilic Ligands

The incorporation of chiral amphiphilic lanthanide-directed self-assembled Nd(III) complexes (Nd.13 and Nd.23) into stable Langmuir monolayers, and the subsequent Langmuir-Blodgett film formation of these, is described. The photophysical properties of the enantiomeric pair of ligands 1 and 2 in the presence of Nd(CF3SO3)3 were also investigated in CH3CN solutions using UV-vis, fluorescence, and lanthanide luminescence spectroscopies. Analysis of the resulting self-assembly processes revealed that two main species were formed in solution,1:1 and 1:3 Nd:L self-assembly complexes, with the latter being the dominant species upon the addition of 0.33 equivalents of Nd(III). Excited state lifetime measurements of Nd.13 and Nd.23 in CH3OH and CD3OD and CH3CN were also evaluated. The formation of the self-assembly in solution was also monitored by observing the changes in the circular dichroism (CD) spectra; and large differences were observed between the 1:3 and other stoichiometries in the spectra, allowing for correlation to be made with that seen in the emission studies of these systems. Surface pressure-area and surface pressure-time isotherms evidenced the formation of stable Langmuir monolayers of Nd.13 and Nd.23 at an air-water interface, and the deposition of these monolayers onto a quartz solid substrate (Langmuir-Blodgett films) gave rise to immobilized chiral monomolecular films which exhibited Nd(III) NIR luminescence upon excitation of the ligand chromophore, demonstrating efficient energy transfer to the Nd(III) excided state (sensitized) with concomitant emission centered at 800 and 1334 nm.

Supramolecular structure formation of Langmuir-Blodgett films of comblike precursor and polyimide

The surface structure of Langmuir-Blodgett films of a comblike polyimide precursor—a rigid-chain polyamic acid alkylamine salt bearing multichains of tertiary amine—and films of the corresponding polyimide were studied by atomic force microscopy (AFM). An analysis of the images of the surface of three-layer films revealed a domain structure. It was found that the Langmuir-Blodgett film formation of the precursor occurs as a result of the layer-by-layer deposition of two-dimensional domains (composed of polyamic acid salt molecules on the water surface) onto a substrate. The formation of domains in a monolayer is associated with the chemical structure of the precursor, to be more precise, with the rigidity of the main chain and the presence of closely spaced aliphatic side chains in the polymer chain, whose total cross-section area is close to the surface area of the projection onto the plane of the repeating unit of the main chain. Polyimide films inherit the domain structure of the precursor films; the inhomogeneity of the film thickness substantially decreases, whereas the domain size and character of their distribution in the film remain unchanged.

Controlling the Structural and Electrical Properties of Diacid Oligo(Phenylene Ethynylene) Langmuir–Blodgett Films

The preparation, characterization and electrical properties of Langmuir-Blodgett (LB) films composed of a symmetrically substituted oligomeric phenylene ethynylene derivative, namely, 4,4'-[1,4-phenylenebis(ethyne-2,1-diyl)]dibenzoic acid (OPE2A), are described. Analysis of the surface pressure versus area per molecule isotherms and Brewster angle microscopy reveal that good-quality Langmuir (L) films can be formed both on pure water and a basic subphase. Monolayer L films were transferred onto solid substrates with a transfer ratio of unity to obtain LB films. Both L and LB films prepared on or from a pure water subphase show a red shift in the UV/Vis spectrum of about 14 nm, in contrast to L and LB films prepared from a basic subphase, which show a hypsochromic shift of 15 nm. This result, together with X-ray photoelectron spectroscopic and quartz crystal microbalance experiments, conclusively demonstrate formation of one-layer LB films in which OPE2A molecules are chemisorbed onto gold substrates and consequently -COO-Au junctions are formed. In LB films prepared on a basic subphase the other terminal acid group is also deprotonated and associates with an Na(+) counterion. In contrast, LB films prepared from a pure water subphase preserve the protonated acid group, and lateral H-bonds with neighbouring molecules give rise to a supramolecular structure. STM-based conductance studies revealed that films prepared from a basic subphase are more conductive than the analogous films prepared from pure water, and the electrical conductance of the deprotonated films also coincides more closely with single-molecule conductance measurements. This result was interpreted not only in terms of better electron transmission in -COO-Au molecular junctions, but also in terms of the presence of lateral H-bonds in the films formed from pure water, which lead to reduced conductance of the molecular junctions.

Optimization of Langmuir-Blodgett Film Formation for Organic-Inorganic Layer Perovskite by Squeeze out Method

In order to obtain the uniform film having well-defined lead halide-based layer perovskite structure, we proposed squeezed opt method. It is found that the optimized condition with respect to docosylammonium bromide is revealed by employing hexadecylammonium bromide among tetradecylammonium bromide, hexadecylammonium bromide and octadecylammonium bromide.

Formation of Complex Langmuir and Langmuir-Blodgett Films of DNA with a Dichain Cationic Surfactant

Formation of complex monolayers between a dichain cationic surfactant, namely, dihexadecyldimethylammonium bromide (DHDAB) and deoxyribonucleic acid (DNA) at the air-water interface was first time systematically investigated here. The adsorption of DNA onto DHDAB monolayer was monitored by observing the surface pressure vs. time graph. The polyion-complex monolayers formed in situ through the electrostatic attraction between cationic DHDAB and the phosphate groups of anionic DNA. The organization of the DNA-DHDAB complex at the air-water interface deduced from surface pressure-area (π-A) isotherms was compared with the spectroscopic data in Langmuir-Blodgett films. Study of UV-Vis absorption spectra of pure DNA solution and DNA adsorbed DHDAB complex Langmuir-Blodgett films confirms the successful transfer of the films onto quartz substrates.