Asymmetric ceramic membranes from Langmuir–Blodgett deposition precursors: deposition of fatty acid salts on porous ceramic substrates

Nanoporous 7930 Vycor silica tubes and mesoporous and macroporous Anopore anodic alumina discs are examined as substrates for the multilayer Langmuir–Blodgett (LB) deposition of Cd, Mg, Zn and Ca salts of the arachidic and stearic fatty acids. Conditions for successful deposition are reported. Under appropriate conditions both mesoporous and macroporous Anopore aluminas allow for a full substrate coverage (maximum degree of deposition, D_d,max→1), while a Vycor substrate imposes a D_d,max⩽0.7 and a mechanism explaining the observed D_d,max values is presented. The produced ceramic oxide–LB film composites are prototype precursors for gas-separating all-ceramic asymmetric membranes, following the application of an oxidative plasma treatment.     

The synthesis of novel perylene-like dyes and their aggregation properties in Langmuir and Langmuir–Blodgett films

The synthesis of novel perylene-like dyes with different length and molecular structure of terminal chains substituted to the main perylene core is described. The dyes are able to form compressible and stable monolayers at the air–water interface (Langmuir films), which can be easily transferred onto solid substrates (Langmuir–Blodgett films). In the Langmuir and Langmuir–Blodgett films, the dye molecules show tendency to creation of self-aggregates, both in the ground and excited electronic states. The influence of the molecular structure of the substituents on the aggregation properties is observed and discussed.     

Deposition of detonation nanodiamonds by Langmuir–Blodgett technique

Langmuir–Blodgett technique, which classically allows preparing monomolecular films, was here used to deposit a film of detonation nanodiamond particles.We proceeded to the functionalization of the nanodiamond (nD) particles so as to obtain hydrophobic nanodiamonds. Cetyltrimethylammonium chloride (C₁₉H₄₂ClN) (CTAC) was used for this purpose in order to form an ionic complex ND–COO^?(NH₃)⁺–R with the functional groups of the nanodiamonds.Compressions with various strengths (10 to 30 mN/m) were performed on the Langmuir–Blodgett device in order to prepare different types of deposits on mica substrates. Atomic Force Microscopy was used to characterize these deposits. It was shown that compressions with low intensity result in discontinuous distributions of the particles on the surface. Conversely, very dense and continuous deposits were observed for higher compression strengths. By optimizing the nD/CTAC ratio in the suspension, a very regular deposit with a monoparticle height was obtained.     

Asymmetric Inorganic Membranes Through Langmuir–Blodgett Deposition and Plasma Processing

Nanoporous 7930 Vycor silica tubes with Langmuir–Blodgett (LB) deposited arachidic acid salts undergo oxidative plasma treatment to yield fully inorganic asymmetric membranes. Membranes from precursors with different numbers of LB layers are examined by differential, integral and relative permeability methods for the determination of the structural characteristics of the separating top layer. The membrane top layer is found to be dominated by medium size micropores, while a small population of defective surface sites (partially covered original pores) is also present. The gas separation potential of inorganic asymmetric membranes from ceramic oxide-LB film composites is discussed.     

Survey on Langmuir–Blodgett Films of Polymer and Polymeric Composite

This article presents a concise review of research performed in the field of Langmuir–Blodgett films. Various types of conducting polymers, piezoelectric/pyroelectric polymers, and ferroelectric polymers have been utilized for fabrication of polymeric and composite Langmuir–Blodgett films. The Langmuir–Blodgett polymers may reveal fine Langmuir–Blodgett behavior such as mechanical robustness, heat resistance, and chemical stability. Moreover, polymers offer recompenses of synthetic tailoring, low-cost, and volume production toward enhanced performance Langmuir–Blodgett materials. The applications of Langmuir–Blodgett films have been reviewed in sensors, electroluminescence devices, polymeric light-emitting diode, and microelectronic devices. Langmuir–Blodgett films represent exciting area of materials science demanding recent research attention.     

Electrophoretic deposition of functionally-graded NiO–YSZ composite films

Functionally-graded NiO–8 mol % YSZ composite films were prepared by a controlled voltage-decay electophoretic deposition (EPD) process. The films consisted of three layers with varying NiO concentrations and porosities. Effects of different parameters including the type of the organic media, solid concentration, NiO:YSZ ratio, and iodine on the stability of EPD suspensions and deposition kinetics were studied. A stable NiO–YSZ suspension was attained in isopropanol with NiO–YSZ ratio of 60:40 and iodine concentration of 0.5 mM. The composite film contained varying NiO concentration from 46 wt.% near the substrate to 32 wt.% close to the electrolyte with 42 wt% NiO in the intermediate region. The thickness of each layer is about 10, 44 and 68 μm, respectively. The prepared anode could be promising for solid oxide full cells as it compromises good contact to the electrode with higher corrosion resistance and active reaction zone with the electrolyte.     

Understanding ferroelectric performances of spin-coated odd–odd nylon thin films

Ferroelectric properties of organic odd–odd nylon spin-coated thin films are investigated. Nylon 11-11, 9-13, and 11-13 are prepared by melt polymerization of the nylon salt consisting of the corresponding dicarboxylic acid and diamine. The obtained nylon is spin coated to obtain thin films with the thicknesses in the range of 85–108 nm. After spin coating, the sample films are subjected to several thermal history procedures, namely the films are either melt quenched or thermally annealed at various temperatures. The melt-quenched films are in the γ crystal phase that is directly related to the ferroelectricity of the sample thin films. Enhanced ferroelectricity is measured for the sample films that are thermally annealed at 165 °C. The remanent polarization is significantly affected by the crystallite size. Ferroelectric switching of the thin films is studied by applying a sinusoidal voltage with the frequencies of 1, 10, 100, 1 k, and 10 kHz. The switching speed is evaluated from the full width at half-maximum of the switching current. A switching speed of 4.7 × 10³ s⁻¹ (switching time of 210 μs) is measured for 1 kHz switching. The remanent polarization is strongly decreased by increasing the switching frequency, whereas the coercive field is increased. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47595.     

The application of Langmuir–Blodgett technique in preparation of the macroporous titania coatings

The aim of this work was preparation of the macroporous titania coatings with the use of the sol–gel process and poly(methylmetacrylate) beads as a template. The effectiveness of the Langmuir–Blodgett (LB) and dip-coating (DC) methods in deposition of polymer beads on the silicon wafers was compared. Resulted polymer layers and final porous titania coatings were analyzed with the use of the atomic force microscope. It was found, that application of the LB is possible only when arachidic acid is present in the subphase. It should be highlighted, that the application of the LB method is the novelty between the methods of the polymer beads arrangement having the diameter of 200–300 nm. Main factors which influence the structure and the arrangement of polymer templates were the concentration of the polymer suspension and the rate of the substrate immersion/withdrawal from the suspension. We established, that the optimal concentrations for preparation of polymer templates, exhibiting good arrangement of individual beads, were 0.5 and 6 % for LB and DC methods, respectively. The size of pores of the obtained macroporous titania (200–330 nm) corresponds well with the size of the polymer beads used as the template (200–235 nm).     

Electrochemical deposition of Co–Sb thin films on nanostructured gold

The electrochemical behavior of the Co–Sb system on Au substrate during cyclic voltammetry and potentiostatic deposition was investigated. Electrochemical behavior of Co and Sb was studied and compared to the Co–Sb system. At a negative potential (−0.9 V vs. Ag/AgCl) the electrochemical behavior of this binary system was similar to that of individual Co and Sb combined. For more negative vertex potentials (e.g., −1.2 V vs. Ag/AgCl), results from cyclic voltammetry have shown the presence of a new compound different from Co and Sb which could only be detected at slow sweep rate. The deposition performed at constant potentials between −1.0 and −1.2 V have resulted in films that were made of CoSb₃ and Sb as indicated by XRD. Surface film studied by SEM and EDS has shown morphological and compositional non-uniformities caused by hydrogen evolution.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.     

Effect of annealing temperature on ferroelectric electron emission of sol–gel PZT films

In this work, the influence of annealing temperature on the ferroelectric electron emission behaviors of 1.3-μm-thick sol–gel PbZr_0.52Ti_0.48O₃ (PZT) thin film emitters was investigated. The results revealed that the PZT films were crack-free in perovskite structure with columnar-like grains. Increasing annealing temperature led to the growth of the grains with improved ferroelectric and dielectric properties. The remnant polarization increased slightly from 35.3 to 39.6 μC/cm² and the coercive field decreased from the 56.4 to 54.6 kV/cm with increasing annealing temperature from 600 to 700 °C. The PZT film emitters exhibited remarkable ferroelectric electron emission behaviors at the threshold voltage above 95 V. The film annealed at 700 °C showed a relatively lower threshold voltage and higher emission current, which is related to the improved ferroelectric and dielectric properties at higher annealing temperature. The highest emission current achieved in this work was around 25 mA at the trigger voltage of 160 V.     

Comparison of a-C:H films deposited from methane–argon and acetylene–argon mixtures by electron cyclotron resonance–chemical vapor deposition discharges

Hydrogenated amorphous carbon (a-C:H) films are deposited from methane–argon and acetylene–argon gas mixtures in a microwave electron cyclotron resonance plasma reactor. The films deposited with the two different gas mixtures under similar input parameter conditions have substantially different properties, including deposition rate, mass density, optical absorption coefficient, refractive index, optical bandgap and hydrogen content. The deposition parameters varied include rf-induced dc substrate bias voltage (0 to −60 V), pressure (1–5 mTorr) and argon/hydrocarbon gas flow ratio (0–1.0). The discharge properties of the two different gas mixtures, including electron temperature, ion saturation current, and residual gas composition of the exit gas flow, are measured to help explain the different deposition results from the two different gas mixtures. The use of lower pressures is found to be critical for obtaining denser, lower hydrogen content films from acetylene. For the methane-deposited films the addition of argon to the discharge increased the film's mass density and lowered the hydrogen content. In both methane- and acetylene-based deposition processes the rf-induced bias is also a critical determining factor of film properties.     

Field emission of ribonucleic acid–carbon nanotube films prepared by electrophoretic deposition

Carbon nanotube (CNT) films are fabricated on indium tin oxide (ITO) glass substrates by combining electrophoresis with photolithography using ribonucleic acid (RNA)–CNT hybrids as functionalized CNTs and their emission properties are investigated. The CNTs are well-dispersed by wrapping them with RNA and well-defined RNA–CNT patterns are obtained on the ITO glass substrate. The RNA–CNT films show good field emission properties, such as high current densities, low turn-on fields, and uniform emission images. The RNA–CNT hybrids compare favorably to other functionalized CNTs for use in the electrophoretic deposition.     

Multilayer zirconium titanate thin films prepared by a sol–gel deposition method

Zirconium titanate multilayer thin films were prepared by an aqueous particulate sol–gel process followed by spin coating. The obtained structures were studied by transmission electron microscope, scanning electron microscope, atomic force microscope, and spectroscopic reflection analyses. According to the results, sound thin films up to three layers were developed, accompanied by an increase in thickness and roughness by increasing the number of the layers. It was also found that the coatings consist of globular nanoparticles with an average diameter of 50 nm. Considering the contribution of roughness to biological responses, the optimization of the surface characteristics to meet an optimal performance seems to be a challenging issue, which demands future studies.     

Impedance spectroscopic studies of sol–gel derived barium strontium titanate thin films

In the present work electroceramic thin films of barium strontium titanate (Ba_1?xSr_xTiO₃ – BST) were deposited on stainless steel substrates by sol–gel technique. Homogeneous Ba_0.6Sr_0.4TiO₃ thin films as well as spatially inhomogeneous BST thin films exhibiting artificial gradients in composition normal to the growth surface were deposited. Both up- and down-graded BST films were fabricated by depositing successive layers with Sr mole fraction x ranging from x = 0.5 to x = 0.3. In the present study the tool of impedance spectroscopy has been used to study the dielectric properties of BST thin films at room temperature. To analyze the impedance spectroscopy data the Nyquist (Z″ vs. Z′) plots as well as the simultaneous representation of the imaginary part of impedance and electrical modulus (Z″, M″) vs. frequency were used. Experimental data were fitted using the CNLS fitting method. Agreement between experimental and simulated data was established. The data indicated that the thin film samples fabricated can be represented by an equivalent circuit with two relaxation frequencies.     

Sol–gel derived PMN–PT thick films for high frequency ultrasound linear array applications

A 12-µm PMN–PT [0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃] thick film was produced by alternate spin-coating of a ceramic powder/sol–gel composite and infiltration of the sol–gel. Using this technique, a high quality PMN–PT thick film was obtained, showing a permittivity ε_r of ~3300 and dielectric loss factor of ~0.02 at 1 kHz. Photolithographic and wet etching techniques were used to fabricate a 32-element linear array from the film. The completed array showed a center frequency of approximately 110 MHz and a bandwidth of 60% at ?6 dB without a matching layer. The performance of the kerfless array was studied and compared to a kerfed array simulated with finite element analysis.     

Preparation of Si–C–N–Fe magnetic ceramic derived from iron-modified polysilazane

In this paper, Si–C–N–Fe magnetoceramics were obtained by pyrolysis of iron-modified polysilazane (PFSZ) precursors which were synthesized by using polysilazane (PSZ) and iron (III) acetylacetonate (Fe(acac)₃) as starting materials. The as-synthesized PFSZ precursors were characterized by Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography. The polymer-to-ceramic conversion of the PFSZ was studied by FT-IR and thermal gravimetric analysis. It is found that the ceramic yield of the PFSZ precursor is ca. 25% higher than that of the original PSZ. The crystallization behavior, microstructures and magnetic properties of the PFSZ-derived Si–C–N–Fe magnetoceramics were studied by techniques such as X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results indicate that the formed α-Fe nanoparticles are uniformly dispersed in amorphous Si–C–N(O) matrix, leading to the soft magnetization of the resultant Si–C–N–Fe ceramics. Moreover, the iron content and the magnetic properties of the Si–C–N–Fe ceramic could be easily controlled by the amount of Fe(acac)₃ in the precursor.     

Flexible magnetoelectric PVDF–CoFe2O4 fiber films for self-powered energy harvesters

Integrating the concept of magnetoelectric in the mechanical energy harvesters through the magneto-mechano-electrical (MME) nanogenerators has been explored to realize the self-powered devices. The magnetoelectric interaction enabled the output performance of the MME nanogenerator under magnetic stimulus of the active components of the energy harvesters. In this perspective, we fabricated a flexible biomechanical and MME nanogenerator using PVDF/CoFe₂O₄ fibers composite films. CoFe₂O₄ fibers were synthesized by the electrospinning technique and the process parameters were optimized to achieve uniform and bead-free fibers. The structural and morphological properties were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The structural and morphology revealed the fibers calcined at 800 °C with a heating rate of 2 °C/min produced bead-free continuous fibers with a fiber diameter of 210 nm with cubic spinel crystalline structure with a crystallite size of 34 nm. These highly crystalline fibers were used to fabricate PVDF/CoFe₂O₄ fibers composite films. The magnetoelectric behaviour of the films verified through polarization vs. electric field (P-E) loops under magnetic field. The leakage current density and mechanism of the composite films were investigated, and it was discovered that the mechanism was due to Schottky emission. Further the energy harvesting performance of the composite films were estimated where the nanogenerator achieved an output voltage of 13 V under biomechanical tapping force while the MME nanogenerator produced 3.5 V under a low frequency stray magnetic field of 6 Oe with a power density of 28 μW/m².     

Collagen–chitosan biocomposites produced using nanocarbons derived from goatskin waste

We report a simple method for the preparation of multifunctional biocomposite films by using collagen-containing waste material trimmed from goatskins. The waste was cleaned and carbonized to synthesize conducting and magnetic graphitic nanocarbon (GrC). Collagen was extracted from the trimmed waste and combined with chitosan and GrC to form flexible, semi-transparent, conductive and magnetic biocomposite films (GrC/Col–Ch) of micron-thickness. Electrical conductivity of the biocomposite films was shown to increase gradually with an increase in the concentration of chitosan and GrC. The tensile strength of the GrC/Col–Ch films increases up to 10 wt.% of GrC loading, above which it decreases due to the high carbon loading, as also shown from fracture surfaces examined by scanning electron microscopy. The small ferromagnetic property of the synthesized biocomposite films has been potentially used for magnetic tracking and actuation.