An infrared study on Langmuir–Blodgett films of octadecylammonium octadecanoate: FWHM and the vibrational coupling

The monolayer of the mixture of octadecanoic acid and octadecylamine with molar ratio 1:1 has been investigated at the air–water interface. It was found that the monolayer shows a rather stable state at the surface pressure of 30 mN/m and this monolayer can be transferred onto a CaF₂ plate by Langmuir–Blodgett (LB) technique. The infrared spectra of LB films indicated that octadecylammonium octadecanoate is formed by an intermolecular proton exchange between adjacent carboxylic and aminic groups (COO⁻ and NH₃⁺). In three-layer LB film, the CH₂ scissoring mode of the long hydrocarbon chains of octadecylammonium octadecanoate shows a broad band feature at about 1468 cm⁻¹ while this vibrational mode of three-layer LB film of the mixture (1:1) of deuterated stearic acid and octadecylamine (octadecylammonium octadecanoate-d35, C₁₈H₃₇NH₃⁺C₁₇D₃₅COO⁻) only shows a narrow band. The broad feature of the CH₂ scissoring mode in octadecylammonium octadecanoate probably originates from the coupling between the chain of stearic acid and that of octadecylamine while this kind of coupling could be completely removed in octadecylammonium octadecanoate-d35. Another conclusion presented in this paper is that there are no couplings among the chains of fatty acid or among the chains of octadecylamine in LB films of octadecylammonium octadecanoate.     

Structural and electrical characterisation of betaine-type,organic, molecular,thin evaporated films and LB multilayers

The structure and electrical properties of highly polar indandione-1,3 pyridinium betaine (IPB) derivatives have been studied in vacuum-evaporated thin films and Langmuir-Blodgett (LB) multilayer assemblies. Phase transitions induced by temperature and/or electric field have been observed in LB films of an amphiphilic derivative of IPB.The LB films of IPB, obtained at room temperature, form a Y-like structure which melts at about 50 °C to produce spherical domains, having Z-like structure, which remain stable up to 110 °C. Similar phase transitions can be induced by an electric field with ε ≥ 2 × 10⁵ V cm⁻¹ at room temperature. In the new Z-like phase of the IPB LB films, the electrical conductivity increases by some five or six orders of magnitude and the activation energy of dark conductivity decreases from 0.18 ± 0.03 eV to practically zero.The vacuum-evaporated IPB films yield low electrical conductivity (σ = 10⁻¹⁵–10⁻¹⁶S cm⁻¹), whereas in the LB multilayers a notable anisotropy of conductivity is observed. In case of coplanar cells the conductivity increases to σ = 10⁻⁸S cm⁻¹. In sandwich-type LB samples the conductivity value is similar to that of the vacuum-evaporated polycrystalline thin films.     

Photophysical and Photoelectric Properties of 2—{[4—（N—Hexadecyl—N—methylamino）phenyl]methylene}—propanedinitrile

2-{[4-(N-Hexadecyl-N-methylamino)phenyl]methylene}-propanedinitrile(HMAPN) with typical donor-π-acceptor(D-π-A）structure was synthesized.It could be easily assembled into stable films by LB technique.The photophysical properties of HMAPN were investigated in solution and on LB films.The photoelectric properties of HMAPN were examined and the anodic photocurrent of the ITO electrode modified by the monolayer LB film of HMAPN was measured as 835 nA/cm^2 under the white light of 218.2 mW/cm^2 without bias voltage.The effects of light intensity,bias voltage on the photocurrent were discussed.The possible mechanism of the photocurrent formation was given.     

Direct fabrication of conductive LB films composed of N-docosylpyridinium-TCNQ

Langmuir-Blodgett (LB) films of N-docosylpyridinium-TCNQ (NDP-TCNQ) were prepared in air. The films deposited at the room temperature showed in-plane conductivity of 4×10-3 S.cm-1 and its absorption spectra in UV and IR regions resembled those for the films composed of mixed-valence TCNQ salts of NDP-(TCNQ)2 rather than for the NDP-TCNQ LB films preparaed under protection of nitrogen. In the case that the films left in a warm environment after each dipping cycle, the absorption in the corresponding region changed. Spectral analysis and XPS study revealed that more TCNQ molecules were produced. The oxidation of TCNQ- in air was considered to be the origin of neutral TCNQ formed.     

An infrared study on Langmuir–Blodgett films of 14,15-bis(hydroxyimino)-13-thiaoctacosane

The Langmuir–Blodgett (LB) films of 14,15-bis(hydroxyimino)-13-thiaoctacosane (TOC) on aluminium plated substrates were investigated using Fourier transform infrared (FTIR), grazing angle (GAIR) and horizontal attenuated total reflectance (HATR) techniques. The LB films of TOC can be transferred onto the solid substrate successfully. The molecular structure of LB films was analysis by comparing the GAIR and HTAR spectra. The intense bands at 2848 and 2918 cm⁻¹ are assigned to symmetric ν_s(CH₂) and asymmetric ν_a(CH₂) stretching vibrations of methylene groups. These peaks suggest that the alkyl chains in TOC are nearly in all-trans conformational state. The presence in the infrared spectra of several bands due to the methylene wagging and twisting modes and of the splitting of the bands due to the methylene scissoring mode at 1467 and 1459 cm⁻¹ and the CH₂ rocking mode at 720 and 731 cm⁻¹ also indicates that in films of TOC alkyl chains are in the all-trans conformation and packed in either an orthorhombic or a monoclinic structure with an orthorhombic subcell containing two mutually orthogonal molecules. Another conclusion presented in this paper that the alkyl chain tilt, which is the angle between the axis, which bisects the C–C bonds and the surface normal, was quite large by comparing the GAIR and HATR spectra.     

LB Film Structure of Nanometer‐Scale PEEKK Macrocyclic Oligomers

A rigid macrocyclic oligomer (RCO), cyclic poly(aryl ether ketone), was synthesized and used to produce Langmuir‐Blodgett (LB) films. The isotherm of surface pressure versus surface area showed that the RCO molecules form a stable monolayer on the water subphase with an area per molecule of about 1.7 nm². The structure of the LB film was confirmed by means of atomic force microscope, and two‐dimensionally ordered cavities of nanometer scale were observed in the LB film.     

Proton Conductivities of Graphene Oxide Nanosheets: Single,Multilayer, and Modified Nanosheets

Proton conductivities of layered solid electrolytes can be improved by minimizing strain along the conduction path. It is shown that the conductivities (σ) of multilayer graphene oxide (GO) films (assembled by the drop‐cast method) are larger than those of single‐layer GO (prepared by either the drop‐cast or the Langmuir‐Blodgett (LB) method). At 60 % relative humidity (RH), the σ value increases from 1×10⁻⁶ S cm⁻¹ in single‐layer GO to 1×10⁻⁴ and 4×10⁻⁴ S cm⁻¹ for 60 and 200 nm thick multilayer films, respectively. A sudden decrease in conductivity was observed for with ethylenediamine (EDA) modified GO (enGO), which is due to the blocking of epoxy groups. This experiment confirmed that the epoxide groups are the major contributor to the efficient proton transport. Because of a gradual improvement of the conduction path and an increase in the water content, σ values increase with the thickness of the multilayer films. The reported methods might be applicable to the optimization of the proton conductivity in other layered solid electrolytes.     

Precursor method for polymeric LB films

First, the general concept of the “Precursor Method” for the preparation of polymeric Langmuir-Blodgett (LB) films that possess no long alkyl chain between film layers, and the preparation of polybenzothiazole 7 LB film are described. The preparation of 7 LB film was carried out by the same procedure as that used to make polyimide LB films via precursor LB films of polyamides that contain β-carboxyethylthio alkylamine salts 6. Precursor 6 LB film had a Y type structure with monolayer thickness of 2.8 nm, while polybenzothiazole 7 LB film had 0.34 nm. The nonlinear susceptibility χ⁽³⁾ of polybenzothiazole 7 LB film in parallel to the dipping direction was 3.8 × 10⁻¹¹ esu, whereas the susceptibility in the perpendicular direction was about one fifth of that of the parallel direction.     

Grain‐Boundary‐Free Super‐Proton Conduction of a Solution‐Processed Prussian‐Blue Nanoparticle Film

A porous crystal family has been explored as alternatives of Nafion films exhibiting super‐proton conductivities of ≥10⁻² S cm⁻¹. Here, the proton‐conduction natures of a solution‐processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono‐particle film of Prussian‐blue NPs is spontaneously formed on a self‐assembled monolayer substrate by a one‐step solution process. A low‐temperature heating process of the densely packed, pinhole‐free mono‐particle NP film enables a maximum 10⁵‐fold enhancement of proton conductivity, reaching ca. 10⁻¹ S cm⁻¹. The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water‐retention ability of the film. In our proposed mechanism, the high‐performing solution‐processed NP film suggests that heating leads to the self‐restoration of hydrogen‐bonding networks throughout their innumerable grain boundaries.     

Electrochemical and XPS measurements on thin oxide films on zirconium

The potentiodynamic growth of thin oxide films on zirconium electrodes was investigated by coulometric and simultaneous impedance measurements, as a function of the electrode potential (0 V ⩽ E ⩽ 9 V), the pH (0 ⩽ pH ⩽ 14) and the surface preparation (electropolishing, etching and mechanical polishing). The initial film thickness d₀ is at least 4–6 nm; with increasing potential, the oxide grows irreversibly by 2.6 nm/V (pH 0.3) up to 3.2 nm/V (pH 14). In Cl⁻- and ClO⁻₄-containing solutions the oxide growth is limited by localized corrosion. The oxide behaves like a typical insulator with a donor concentration N_D < 10¹⁹ cm⁻³ and a dielectric constant D = 31. Below −0.5 V (vs. SHE) only, th film behaves like an n-type semiconductor with N_D ≈ 3 × 10¹⁹ cm⁻³. From photoelectrochemical measurements a direct and an indirect transition with band gap energies of E_g = 5 eV and E_g = 2.8 eV could be derived. Anodic electron-transfer reactions (ETRs) are blocked at the homogeneous oxide surface, but cathodic ETRs are possible at larger overvoltages. Near the flatband potential E_fb ≈ −1.3 ± 0.2 V (vs. SHE) hydrogen evolution takes place with a simultaneous increase of the capacity which may be attributed to hydrogen incorporation. With XPS measurements the stoichiometry of the oxide film was determined as ZrO₂ at all the pH values examined, but a thin outer layer contained some hydroxide. Components of the forming electrolyte could not be detected (sulphate, borate and perchlorate < 1%), but etching in HF caused accumulation of F⁻ at the inner boundary.     

Chemically Gradient Hydrogen-Bonded Organic Framework Crystal Film

Hydrogen-bonded organic frameworks (HOFs) are ordered supramolecular solid structures, however, nothing much explored as centimetre-scale self-standing films. The fabrication of such crystals comprising self-supported films is challenging due to the limited flexibility and interaction of the crystals, and therefore studies on two-dimensional macrostructures of HOFs are limited to external supports. Herein, we introduce a novel chemical gradient strategy to fabricate a crystal-deposited HOF film on an in situ-formed covalent organic polymer film (Tam-Bdca-CGHOF). The fabricated film showed versatility in chemical bonding along its thickness from covalent to hydrogen-bonded network. The kinetic-controlled Tam-Bdca-CGHOF showed enhanced proton conductivity (8.3×10⁻⁵ S cm⁻¹) compared to its rapid kinetic analogue, Tam-Bdca-COP (2.1×10⁻⁵ S cm⁻¹), which signifies the advantage of bonding-engineering in the same system.     

Alignment of liquid crystals using Langmuir‒Blodgett films of unsymmetrical bent-core liquid crystals

ABSTRACT

The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air–water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir?Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.     

Theoretical study of sorption-induced bending of polypyrrole films

Polypyrrole films containing perchlorate were electrochemically synthesized and the bending and recovery motion of the films obtained has been investigated. It was found that the thickness of the film and ambient relative humidity (RH) were crucial to the motion of film: An increase of the film thickness decreased the displacement of the bending but increased the bending stress. On the other hand, an increase of the ambient RH decreased both functions. The motion of film was caused by the difference of expansion on both sides of the film owing to anisotropic sorption of water vapor, which could be expressed by the diffusion-limited bending model. The diffusion coefficients calculated from the bending and recovery motion at 25°C, RH 50% were 12.2 × 10⁻⁸ cm² s⁻¹ and 3.5 × 10⁻⁸ cm² s⁻¹, respectively. The maximum expansion of the film surface calculated from the bending curve was about 0.36%. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2237–2246, 1998     

Biomimetic synthesis of the arachidic acid/Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>S nanocomposite films

Ag _x Cd _y S nanoparticles were obtained in arachidic acid (AA) monolayer containing Ag⁺ and Cd²⁺ under H₂S flow. The AA/Ag _x Cd _y S monolayers were deposited onto solid substrate to prepare LB films. The UV-vis spectrum showed that the LB film exhibited notable quantum-size effect. The small-angle X-ray diffraction revealed periodic structure of the LB films. The molar ratio of Ag to Cd in AA/Ag _x Cd _y S film was ca. 1 : 5 as measured by the XPS. TEM and FTIR spectroscopy showed that the head-groups of arachidic acid molecules controlled formation of Ag _x Cd _y S nanoparticles in the monolayer.     

Characterization of CdS nanoparticles formed and aggregated in stearic acid Langmuir–Blodgett films by atomic force microscopy

Alternate films, which are composed of stearic acid and CdS nanoparticles were synthesized by exposing Langmuir–Blodgett (LB) films of cadmium stearate (CdSt₂) to H₂S gas at a pressure of 1 Torr. The changes of surface morphology of film with the increased reaction time were directly observed by atomic force microscopy for the first time. Before being exposed to H₂S, the surface of CdSt₂ LB film was homogeneous from microscale down to nanoscale, and it was observed that CdSt₂ molecules formed a well orderly rectangular herringbone lattice structure on the molecular scale. However, after being exposed to H₂S the ordered CdSt₂ molecules gradually changed into a disordered state, and eventually the LB film surface became rough with the apparent feature of bulk structures on the nanoscale. This change in the morphology can be attributed to the aggregation of buried CdS nanoparticles within LB films, which has been confirmed by a structured UV–visible absorption spectrum where the absorption edge is red-shifted about 0.7 eV with respect to bulk CdS. Finally, the aggregation mechanism of CdS in the LB film was analyzed.     

Grain-Boundary-Free Super-Proton Conduction of a Solution-Processed Prussian-Blue Nanoparticle Film

A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10⁻² S cm⁻¹. Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 10⁵-fold enhancement of proton conductivity, reaching ca. 10⁻¹ S cm⁻¹. The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.     

Surface-plasmon optical characterisation of asymmetric soap films

Stable water films covered by arachidic acid monolayers were prepared on vertically arranged glass/Ag/SiO₂-substrates, which were partially pulled out of a film balance trough. The thickness profiles were recorded by on-line-measurement, using the thickness dependence of the dispersion of surface plasmon polaritons. The surface plasmon imaging technique allows for a thickness resolution of 0.2 nm and a height resolution of ca. 20 μm. Variations of these profiles as a function of the lateral pressure of the horizontal arachidate layer on the film balance were observed. For the first time Raman studies were made on asymmetric soap films. The intensity ratio of the Δη_a = 2800 cm⁻¹ to the Δη_s = 2850 cm⁻¹ line in the CH-stretching vibration range shows a dependence on the lateral pressure in the monolayer.     

Rate constants and vibrational distributions for water-forming reactions of OH and OD radicals with thioacetic acid, 1,2-ethanedithiol and tert-butanethiol

Reactions of OH and OD radicals with CH₃C(O)SH, HSCH₂CH₂SH, and (CH₃)₃CSH were studied at 298 K in a fast-flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + CH₃C(O)SH reaction and (3.8 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + HSCH₂CH₂SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H₂S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C₂H₅)₂S reference reaction, the rate constant for the OD + (CH₃)₃CSH reaction was estimated to be (3.6 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Vibrational distributions of the H₂O and HOD molecules from the title reactions are typical for H-atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.     

Kinetics of proton transfer in ice via the pH-jump method: Evaluation of the proton diffusion rate in polycrystalline doped ice

The value of the proton diffusion coefficient D_H⁺ in ice was extracted from the diffusion-controlled rate k_D of the proton recombination reaction RO⁻ + H₃O⁺ → k_D ROH + H₂O in polycrystalline doped ice. At −10°C, D_H⁺ was estimated to lie between 3.5×10⁻⁶ and 1.3×10⁻⁵ cm² s⁻¹, well below the corresponding value of (4.1 ± 0.1)×10⁻⁵ cm² s⁻¹ found in supercooled water.     

Preparation,characterization, and electrical properties of dual‐emissive Langmuir‐Blodgett films of some europium‐substituted polyoxometalates and a platinum polyyne polymer

A new series of organometallic/inorganic composite Langmuir‐Blodgett (LB) films consisting of a rigid‐rod polyplatinyne polymer coordinated with 2,7‐bis(buta‐1,3‐diynyl)‐9,9‐dihexylfluorene (denoted as PtP) as the π‐conjugated organometallic molecule, an europium‐substituted polyoxometalate (POM; POM = Na₉EuW₁₀O₃₆, K₁₃[Eu(SiW₁₁O₃₉)₂] and K₅[Eu(SiW₁₁O₃₉)(H₂O)₂]) as the inorganic component, and an amphiphilic behenic acid (BA) as the auxiliary film‐forming agent were prepared. Structural and photophysical characterization of these LB films were achieved by π–A isotherms, absorption and photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and low‐angle X‐ray diffraction. Our experimental results indicate that stable, well‐defined, and well‐organized Langmuir and LB films are formed in pure water and POM subphases, and the presence of Eu‐based POM in the subphase causes an area expansion. It is proposed that a lamellar layered structure exists for the PtP/BA/POM LB film in which the POM and PtP molecules can lay down with the interfacial planes. Luminescence spectra of the prepared hybrid LB films show that near‐white emission spectra can be obtained due to the dual‐emissive nature of the mixed PtP/POM blends. These Pt‐polyyne‐based LB films displayed interesting electric conductivity behavior. Among them, PtP/BA/POM 13‐layer films showed a good electrical response, with the tunneling current up to ±100 nA when the voltage was monitored between ?1 and 7 V. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 879–888, 2010