Formation Of Composite Films Research Articles

Hybrid GaAs-Nanowire–Carbon-Nanotube Flexible Photovoltaics

A simple method is described for the preparation of carbon nanotube (CNT) composite films containing Au nanoparticles, which act as adatom collection agents promoting the growth of core-shell p-n junction GaAs nanowires (NW), according to the vapor-liquid-solid mechanism. This approach for composite film formation requires no covalent modification of the CNTs. GaAs NWs obtained are randomly aligned with respect to the CNT substrate in a densely packed arrangement. Nanohybrid films, incorporating coaxial GaAs NWs as the active, light-harvesting medium are used in the fabrication of photovoltaic cells, exhibiting conversion efficiencies up to 0.32%. Doping experiments confirm that conduction is not dominated by Schottky barriers at contact interfaces. The NW/CNT solar cells are shown to retain function following bending up to a curve radius of 12.5 mm, illustrating the potential of these novel materials in flexible device applications.

Electrodeposition of chitosan–hemoglobin films

Electrochemical method has been developed for the fabrication of chitosan–hemoglobin films. The proposed deposition mechanism involved pH changes at the electrode surface attributed to electrochemical reactions, electrophoretic motion of cationic chitosan and hemoglobin macromolecules, coagulation and film formation at the electrode surface. The results of deposition yield measurements, and Fourier transform infrared spectroscopy and circular dichroism spectroscopy studies showed the formation of composite films containing hemoglobin in a chitosan matrix. Electron microscopy studies showed that the film thickness can be varied in the range of 0–2 μm by the variation of deposition time at a constant deposition voltage. The films were investigated for applications in biosensors.

Biocompatible/bioabsorbable silver nanocomposite coatings

AbstractA novel biomass‐mediated method to synthesize cellulose‐stabilized silver nanoparticles (SNPs) and incorporate them into biocompatible/bioabsorbable poly‐L‐lactic acid (PLLA) for producing SNP–PLLA nanocomposite thin films was developed and the antimicrobial efficacy and biocompatibility of the SNP–PLLA films were studied. The formation and coating morphology of SNPs were characterized with UV–visible spectrophotometry and transmission electron microscopy (TEM), and the release rate of silver ion from the SNP–PLLA films was determined by inductively coupled plasma‐optical emission spectrometry. Antimicrobial testing of the SNP–PLLA films performed with Staphylococcus aureus and Escherichia coli according to ISO 22196 standards demonstrated that the SNP–PLLA nanocomposite films with a SNP concentration of 700 ppm reduced colonies forming unit (CFU) counts by 99.8 and 99.99%, respectively. Despite the significant antimicrobial activity, the nanocomposite films with the same SNP concentration had little effect on the viability of human HeLa cells. This strategy that has been developed for the synthesis of nanoparticles and the formation of composite films demonstrates promise for reducing perioperative surgical site infections associated with indwelling devices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of phenolic molecules on electrophoretic deposition of manganese dioxide–carbon nanotube nanocomposites

Electrophoretic deposition (EPD) method has been developed for the fabrication of manganese dioxide (MD)–multiwalled carbon nanotubes (MWCNTs) nanocomposites. Cationic tyramine hydrochloride (TA) and anionic gallic acid (GA), chromotropic acid disodium salt (CA) and benzoic acid (BA) were investigated as charging additives. The results of deposition yield measurements, quartz crystal microbalance studies and Fourier transform infrared spectroscopy data showed that OH groups are involved in the adsorption of the phenolic compounds on the MD nanoparticles. The adsorption mechanism is based on the deprotonation of the OH groups and surface complexation of Mn ions. It was shown that the phenolic molecules, such as TA, GA and CA can be used as charging additives for the EPD of MD. Composite MD–MWCNTs films were prepared by cathodic and anodic EPD using TA and GA, respectively. In this approach, TA and GA were used as common charging additives for two different materials: MD and MWCNTs. Scanning electron microscopy studies showed the formation of composite films containing well-dispersed MWCNTs in the MD matrix. The results of the thermogravimetric analysis demonstrated that the amount of the MWCNTs in the composite materials can be varied. The composite films were studied for the application in electrochemical supercapacitors (ES). The ES electrodes showed good capacitive behavior in the 0.5 M Na 2SO 4 electrolyte in a voltage window of 0–0.9 V versus a standard calomel electrode (SCE). The films prepared by cathodic EPD showed higher specific capacitance (SC) compared to the films prepared by anodic EPD with the highest SC of 553 F g −1 at the scan rate of 2 mV s −1.

Electrophoretic Deposition of Ceramic Nanoparticles

An electrophoretic deposition (EPD) method has been developed for the deposition of nanostructured zinc oxide (ZnO) and TiO2 films. It was shown that the stabilization and charging of the nanoparticles in suspensions can be achieved using organic molecules, such as dopamine and alizarin yellow (AY) dye, which were adsorbed on the oxide nanoparticles. Fourier-transform infrared spectroscopy investigations showed that the adsorption mechanism is based on the complexation of metal ions at the surfaces of oxide nanoparticles. Cationic dopamine additive was used for the formation of deposits by cathodic EPD. The adsorption of anionic AY on the oxide nanoparticles resulted in charge reversal and enabled the formation of anodic deposits. The method enabled the codeposition of ZnO and TiO2 and the formation of composite films. It was shown that the deposition yield and deposit composition can be controlled by the variation of deposition time and suspension composition. The deposits were studied using X-ray diffraction and electron microscopy. The deposition mechanism and kinetics of deposition are discussed.

A kinetic study of in situ polyaniline–gold composite film formation

Chloroaurate acid (HAuCl4) was used as an oxidant and aniline (ANI) was used as a reducing agent to prepare a polyaniline–gold (PANI-Au) composite film by in situ polymerization. The formation of the composite film was monitored using a quartz crystal microbalance (QCM). The effects of the concentrations of HAuCl4 and ANI as well as the reaction temperature on the formation of the PANI-Au composite film are discussed. The kinetics of the reaction were investigated by the QCM technique. The results indicate that the kinetics of the reaction are of order 0.5 with respect to HAuCl4 and 1.5 with respect to aniline. The film growth rate increased with increasing ANI, HAuCl4 concentration and reaction temperature. The activation energy calculated from the temperature dependence of the growth rate was 40.32 ± 0.15 kJ/mol. In situ UV-visible spectra of the reaction process were obtained and compared to the reaction process using the QCM technique.

Electrodeposition of hyaluronic acid and composite films

The electrodeposition method has been developed for the fabrication of hyaluronic acid films from sodium hyaluronate solutions. The amount of the deposited material increased with increasing deposition time, resulting in the formation of 0·1–3 μm thick films. The co-deposition of hyaluronic acid and hydroxyapatite (HA) resulted in the fabrication of novel nanocomposite films by electrodeposition. In the proposed method, hyaluronate provided electrosteric stabilisation and charging of HA particles. Deposit composition can be varied by the variation of HA concentration in the sodium hyaluronate solutions. The method enabled the formation of composite films of different thicknesses in the range of 0·1–100 μm. Obtained films were studied by X-ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy and Fourier transform infrared spectroscopy. Composite films showed corrosion protection of stainless steel substrates in Ringer’s physiological solutions. The mechanism of deposition is discussed.

Preparation of nanostructured Al 2O 3–TiO 2 composite films by MOCVD

Nanostructured Al 2O 3–TiO 2 composite films were prepared on glass substrates by metalorganic chemical vapor deposition (MOCVD) using aluminum acetylacetonate and titanium tetraisopropoxide precursors. Oxygen and argon were used as the reactive and carrier gases, respectively. Deposition temperature ( T dep) was varied from 723 to 873 K and total pressure was kept constant at 133–266 Pa. The formation of composite films was achieved by mixing the precursor vapors, which were obtained by heating the aluminum and titanium precursors at 403 and 323–353 K, respectively. The films were characterized by XRD, SEM, EPMA and TEM. The crystalline structure and the surface morphology of the nanostructured Al 2O 3–TiO 2 composite films were strongly dependent on the precursor and deposition temperatures.

Poly (styrene) latex/modified Na-activated bentonite nanocomposite films: A fluorescence study

We studied film formation of composites of surfactant-free polystyrene (PS) nanoparticles and modified Na-activated bentonite (MLB), by steady state fluorescence (SSF) technique. The films were prepared from a mixture of pyrene (P)-labeled PS particles and MLB at various compositions at room temperature. These films were annealed at elevated temperatures above the glass transition ( T g) temperature of polystyrene for 10 min. Scattered light ( I s) and fluorescence intensities ( I P) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the composite films was monitored by using photon transmission intensity, I tr. Atomic force microscopy (AFM) was used to detect the variation in physical structure of annealed composite films. The nanocomposite films exhibited a percolation threshold at 20 wt.% MLB content. Below this fraction two distinct film formation stages were observed which are known as void closure and interdiffusion and above this fraction no film formation was detected. At 0–20 wt.% MLB, minimum film formation, T 0, void closure, T v and healing, T h temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. Void closure activation energies decreased as the percent of MLB increased, no variation was observed in backbone activation energies.

Formation of composite films of ion-track membranes embedded with oblique Cu nanowires for anisotropic infrared absorption

Composite films of poly(ethylene terephthalate) (PET) embedded with Cu nanowires were prepared by electroplating ion-track PET membranes. PET films were irradiated with 450 MeV 129Xe 23+ ions with a direction of 45° from the film normal, and then etched with sodium hydroxide solution to form thin pores of 1 μm diameter. Cu was filled into the pores by electroplating in a copper sulfate solution to form Cu nanowires embedded in a direction tilted from the film normal. The composite membrane showed anisotropic infrared absorption in the in-plane direction, having the transmission axis in the direction normal to the ion incidence.

Studies on spray deposited NiO–SDC composite films for solid oxide fuel cells

Adherent, porous and catalytically active composite films of NiO–SDC (Ce 0.8Sm 0.2O 1.9), cermet were synthesized by spray pyrolysis technique at substrate temperature 350 °C and annealing temperature 500 °C. X-ray diffraction studies confirmed the formation of composite film with separate phases corresponding to cubic NiO and SDC. SEM study has shown the formation of non-uniform film consisting of three-phase boundaries between pores, NiO and SDC phases. EDAX studies revealed the presence of Ce, Sm and Ni elements in the film. From AFM study, grain size and surface roughness of the film were found to be 30 and 3 nm, respectively. Catalytic activity of the film was studied in the presence of hydrogen and found to increase with increase in temperature. In higher frequency region, the impedance response was a single semicircle, corresponding to the oxygen ion migration in the bulk. Frequency dependent properties, such as AC conductivity, dielectric constant and dielectric loss were also studied. The AC conductivity of the film increased with increase in frequency, showing the conduction through small polaron hopping mechanism, which is favorable for NiO–SDC composite to be used as an anode material in solid oxide fuel cells.

The effect of clay particles on film formation from polystyrene latex

AbstractFilm formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence intensity (IP) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T0, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers

Growth and Photoluminescence Characterization of Highly Oriented CuI/β-Cyclodextrin Hybrid Composite Film

A highly (111) oriented CuI/beta-cyclodextrin inorganic/organic composite film on glass substrates was deposited from a dispersion of CuI and beta-cyclodextrin in a mixture of acetonitrile and dimethylformamide (DMF) solvents, in which DMF plays an important role in the orientation of CuI film. The composite film exhibits obviously improved band gap photoluminescence compared with that of the pure CuI film due to the passivation of iodine-related defect sites by beta-cyclodextrin matrix. This result indicates that the optical properties of CuI film can be easily adjusted by the formation of composite film with proper ligand agents.

Electrochemical Codeposition of Platinum and Molybdenum Oxides: Formation of Composite Films with Distinct Electrocatalytic Activity for Hydrogen Peroxide Detection

AbstractThe electrochemical properties of gold electrode surfaces modified by molybdenum oxide films intercalated with platinum microparticles have been described. The incorporation of Pt microparticles at the oxide film was characterized by PIXE (particle induced X‐ray emission) spectroscopy. The modified electrode showed electrochemical activity at around −0.5 V in 50 mmol L−1 Na2SO4 supporting electrolyte (pH 3), corresponding to the reduction of protons at platinum sites and further transfer of hydrogen atoms to form reduced molybdenum oxides (bronzes). At 0.1 V, the MoO3 / Pt electrode showed a better performance for hydrogen peroxide oxidation than on platinized gold electrodes. The solution pH has a marked effect on the voltammetric profile and best responses for hydrogen peroxide were obtained at the 5.0 to 6.0 pH range. The activation of the electrode by polarization at negative potentials was also studied and a mechanism by which more platinum sites are available as a consequence of this process was proposed. Calibration plots for hydrogen peroxide were highly linear (r=0.9989) in the 0.2 to 1.6 mmol L−1 concentration range, with a relative standard deviation (RSD)<1%.

Electrodeposition of composite films consisting of polypyrrole and mesoporous silica

Electrochemical formation of composite films consisting of polypyrrole (PPy) and MCM particles has been presented, in which pyrrole is electrochemically oxidized in an aqueous solution with suspension of purely siliceous or aluminum-containing MCM-41. The composite films were characterized by scanning electron microscopy, X-ray diffraction and infrared reflection spectroscopy, and the electrochemical response of the PPy/MCM-deposited electrode to Fe(CN) 6 3− investigated. From IR spectra, it is indicated that the polymerization of pyrrole takes place on the internal wall of MCM particles where the cationic PPy is charge-balanced by the negatively charged MCM. A PPy/SiMCM composite electrode prepared in the presence of higher concentration of pyrrole (≧0.5 M) shows a reproducible electrochemical response for Fe(CN) 6 3−. The CV curve on this electrode is comparable to that on pure PPy-modified electrode, and it is suggested that the negative charge on the mesopore surface is almost completely neutralized by the positive charge of PPy.

Spontaneous Potential Oscillations in the Cu(II)/Tartrate and Lactate Systems, Aspects of Mechanisms and Film Deposition

Spontaneous oscillations in the cathode potential are observed in the alkaline Cu(II)/tartrate and lactate systems when applying current to the electrochemical cell. In the Cu(II)/tartrate system the oscillations induce formation of composite films of Cu and on the cathode with a grain size ranging from about 5 to 15 nm. The oscillation period is a function of pH and deposition temperature. A mechanism for the oscillating Cu(II)/tartrate and lactate systems is proposed based on pH changes close to the electrode surface during the deposition process. © 2001 The Electrochemical Society. All rights reserved.

Lowering the percolation threshold of conductive composites using particulate polymer microstructure

The percolation thresholds of carbon black–polymer composites have been successfully lowered using particulate polymer starting materials (i.e., latex and water-dispersible powder). Composites prepared using carbon black (CB) and commercial poly(vinyl acetate) (PVAc) latex exhibit a percolation threshold near 2.5 vol % CB. This threshold value is significantly lower than that of a comparable reference composite made from poly(N-vinylpyrrolidone) (PNVP) solution and the same CB, which exhibits a sharp rise in electrical conductivity near 15 vol % CB. This dramatic difference in critical CB concentration results from the segregated microstructure induced by the latex during composite film formation. Carbon black particles are forced into conductive pathways at low concentration because of their inability to occupy volume already claimed by the much larger latex particles. There appears to be good qualitative agreement between experimental findings and current models dealing with conductive behavior of composites with segregated microstructures. Lack of quantitative agreement with the models is attributed to the polydispersity of the polymer particles in the latex. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 692–705, 2001

Studies on the Formation of DNA−Cationic Lipid Composite Films and DNA Hybridization in the Composites

The formation of composite films of double-stranded DNA and cationic lipid molecules (octadecylamine, ODA) and the hybridization of complementary single-stranded DNA molecules in such composite films are demonstrated. The immobilization of DNA is accomplished by simple immersion of a thermally evaporated ODA film in the DNA solution at close to physiological pH. The entrapment of the DNA molecules in the cationic lipid film is dominated by attractive electrostatic interaction between the negatively charged phosphate backbone of the DNA molecules and the protonated amine molecules in the thermally evaporated film and has been quantified using quartz crystal microgravimetry (QCM). Fluorescence studies of DNA−ODA composite films obtained by sequential immersion of the ODA matrix in the complementary single-stranded DNA solutions using ethidium bromide intercalator clearly showed that the hybridization of the DNA single strands had occurred within the composite film. Furthermore, fluorescence studies of the p...

Lowering the percolation threshold of conductive composites using particulate polymer microstructure

The percolation thresholds of carbon black–polymer composites have been successfully lowered using particulate polymer starting materials (i.e., latex and water-dispersible powder). Composites prepared using carbon black (CB) and commercial poly(vinyl acetate) (PVAc) latex exhibit a percolation threshold near 2.5 vol % CB. This threshold value is significantly lower than that of a comparable reference composite made from poly(N-vinylpyrrolidone) (PNVP) solution and the same CB, which exhibits a sharp rise in electrical conductivity near 15 vol % CB. This dramatic difference in critical CB concentration results from the segregated microstructure induced by the latex during composite film formation. Carbon black particles are forced into conductive pathways at low concentration because of their inability to occupy volume already claimed by the much larger latex particles. There appears to be good qualitative agreement between experimental findings and current models dealing with conductive behavior of composites with segregated microstructures. Lack of quantitative agreement with the models is attributed to the polydispersity of the polymer particles in the latex. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 692–705, 2001

Preparation of CaCO 3 /polymer composite films via interaction of anionic starburst dendrimer with poly(ethylenimine)

The CaCO3/poly(ethylenimine) composite film was obtained in the presence of anionic poly(amidoamine) (PAMAM) dendrimer (G=3.5), whereas the formation of composite film was not observed without PAMAM dendrimer or with PAMAM dendrimer (G=1.5) judging from the results of scanning electron micrographs (SEM). The crystal phase of the CaCO3 film formed was found to be calcite by FT-IR and XRD analysis. The adsorption of PAMAM dendrimer on poly(ethylenimine) film might cause local high concentration of calcium ion and induce a formation of the CaCO3 film.