Functional Composite Films Research Articles

Template-Free Mesoporous Electrochromic Films on Flexible Substrates from Tungsten Oxide Nanorods.

Low-temperature processed mesoporous nanocrystal thin films are platforms for fabricating functional composite thin films on flexible substrates. Using a random arrangement of anisotropic nanocrystals can be a facile solution to generate pores without templates. However, the tendency for anisotropic particles to spontaneously assemble into a compact structure must be overcome. Here, we present a method to achieve random networking of nanorods during solution phase deposition by switching their ligand-stabilized colloidal nature into a charge-stabilized nature by a ligand-stripping chemistry. Ligand-stripped tungsten suboxide (WO2.72) nanorods result in uniform mesoporous thin films owing to repulsive electrostatic forces preventing nanorods from densely packing. Porosity and pore size distribution of thin films are controlled by changing the aspect ratio of the nanorods. This template-free mesoporous structure, achieved without annealing, provides a framework for introducing guest components, therefore enabling our fabrication of inorganic nanocomposite electrochromic films on flexible substrates. Following infilling of niobium polyoxometalate clusters into pores and successive chemical condensation, a WOx-NbOx composite film is produced that selectively controls visible and near-infrared light transmittance without any annealing required. The composite shows rapid switching kinetics and can be stably cycled between optical states over 2000 times. This simple strategy of using anisotropic nanocrystals gives insight into mesoporous thin film fabrication with broader applications for flexible devices.

Influence of sintering temperature on morphology and electrochemical performance of LSCF/GDC composite films as efficient cathode for SOFC

Functional composite cathode films of 56:44wt. % La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)/Ce0.9Gd0.1O2-δ (GDC) films with two different microstructures denoted as coral and columnar were coated on a dense GDC electrolyte by electrostatic spray deposition (ESD) technique. The sintering temperature (Ts) was varied on the ESD films from 800 to 1100°C in air to investigate the influence of sintering conditions on the microstructure, crystalline phases and electrode performances. The amount of porosity, grain growth and electrochemical performance were monitored for both microstructures by combining scanning electron microscope, x-ray diffraction and electrochemical impedance spectroscopies. The microstructures showed marked differences at the micro and nano-scales. The films with lower deposition temperature (columnar film, 300°C) were observed to have accelerated and uncontrolled grain growth and inhomogeneous size distribution at elevated Ts than films with higher deposition temperature (coral film, 350°C). Regardless of the microstructure, as low as 0.05±0.01Ωcm2 at 650°C were measured for the films sintered at low Ts (800-900°C). The differences in resistance and activation energy values were evidenced at high Ts (≥1000°C). The electrochemical processes are discussed in terms of resistance, capacitance and frequency distribution. This study reveals that ESD processing parameters play a critical role in sintering behavior and electrode performances of composite cathode films, mainly at high Ts (≥1000°C).

Preparation of hydrophobic SiO2@(TiO2/MoS2) composite film and its self-cleaning properties

TiO2/MoS2 composite was encapsulated by hydrophobic SiO2 nanoparticles using a sol–gel hydrothermal method with methyltriethoxysilane (MTES), titanium tetrachloride (TiCl4), and molybdenum disulfide (MoS2) as raw materials. Then, a novel dual functional composite film with hydrophobicity and photocatalytic activity was fabricated on a glass substrates via the combination of polydimethylsiloxane adhesives and hydrophobic SiO2@(TiO2/MoS2) composite particles. The influence of the mole ratios of MTES to TiO2/MoS2 (M:T) on the wettability and photocatalytic activity of the composite film was discussed. The surface morphology, chemical compositions, and hydrophobicity of the composite film on the glass substrate were investigated by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angle (water CA) measurements. The results indicated that the composite film exhibited stable superhydrophobicity and excellent photocatalytic activity for degradation of methyl orange (MO) even after five continuous cycles of photocatalytic reaction when M/T was 7:1. The water CA and degradation efficiency for MO remained at 154° and 94%, respectively. Further, the composite film showed a good non-sticking characteristic with the water sliding angle (SA) at about 4°. The SiO2@(TiO2/MoS2) composite consisting of hydrophobic SiO2 nanoparticles and TiO2/MoS2 heterostructure could provide synergistic effects for maintaining long-term self-cleaning performance.

Achieving 3-D Nanoparticle Assembly in Nanocomposite Thin Films via Kinetic Control

Nanocomposite thin films containing well-ordered nanoparticle (NP) assemblies are ideal candidates for the fabrication of metamaterials. Achieving 3-D assembly of NPs in nanocomposite thin films is thermodynamically challenging as the particle size gets similar to that of a single polymer chain. The entropic penalties of polymeric matrix upon NP incorporation leads to NP aggregation on the film surface or within the defects in the film. Controlling the kinetic pathways of assembly process provides an alternative path forward by arresting the system in nonequilibrium states. Here, we report the thin film 3-D hierarchical assembly of 20 nm NPs in supramolecules with a 30 nm periodicity. By mediating the NP diffusion kinetics in the supramolecular matrix, surface aggregation of NPs was suppressed and NPs coassemble with supramolecules to form new 3-D morphologies in thin films. The present studies opened a viable route to achieve designer functional composite thin films via kinetic control.

Electrophoretic deposition of functional organic molecules and composite films

ABSTRACT2,2′-Bicinchoninic acid (BiqCOOH) exhibits a set of functional properties, which motivated the work of fabricating BiqCOOH films. Thin films of BiqCOOH were prepared potentiodynamically or under constant-voltage conditions from the solutions of dipotassium salt of 2,2′-bicinchoninic acid (BiqCOOK) in water or ethanol-water solvent. Electron microscopy investigations showed that the electrochemical assembly of BiqCOOH in aqueous solutions resulted in fibrous morphology while a flower-like morphology, containing rectangular prism-shaped particles, was the result in ethanol-water solutions. The anodic deposition mechanism for BiqCOOH has been proposed based on the analysis of cyclic voltammetry (CV), electron microscopy and FTIR data. The polyaromatic BiqCOOK molecules, containing chelating ligands, showed adsorption on a range of different materials, such as Pd, NiO and multi-walled carbon nanotubes (MWCNT). An electrophoretic deposition (EPD) method allowed for the manufacturing of Pd, NiO and MWCNT films using BiqCOOK as anionic dispersing and binding species. The results of this investigation have generated new possibilities in creating individual material and composite films for applications based on their functional properties.

Influence of gold species (AuCl4(-) and AuCl2(-)) on self-assembly of PS-b-P2VP in solutions and morphology of composite thin films fabricated at the air/liquid interfaces.

Composite thin films doped with Au species were fabricated at an air/liquid interface via a series of steps, including the mass transfer of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) across the liquid/liquid interface between a DMF/CHCl3 solution and an aqueous solution containing either AuCl4(-) or AuCl2(-), self-assembly of PS-b-P2VP in a mixed DMF-water solution, and adsorption and further self-organization of the formed aggregates at the air/liquid interface. This is a new approach for fabricating composite polymer films and can be completed within a very short time. AuCl4(-) and AuCl2(-) ions were found to significantly influence the self-assembly behavior of the block copolymer and the morphologies of the composite films, leading to the formation of nanowire arrays and a foam structure at the air/liquid interface, respectively, which originated from rod-like micelles and microcapsules that had formed in the respective solutions. The effect of the metal complex was analyzed based on the packing parameters of the amphiphilic polymer molecules in different microenvironments and the interactions between the pyridine groups and the metal chloride anions. In addition, these composite thin films exhibited stable and durable performance as heterogeneous catalysts for the hydrogenation of nitroaromatics in aqueous solutions.

Progress in layer-by-layer assembly method of nanocomposite film based on layered double hydroxides

Layered double hydroxides (LDHs) are a class of layered inorganic compounds with highly ordered guest molecules or ions between the host layers. Abundant intercalation assembly chemistry makes LDHs widely applied in adsorption, catalysis, photochemistry, electrochemistry, biomedicine, energy and other fields. Recent years, the fabrication and application of composite ultra-thin films based on LDHs have attracted great interest from domestic and foreign researchers. This review focuses on the development of the delamination of LDHs layered structure and new layer by layer assembly process for LDHs-based composite ultrathin films, in which the driving force for assembly, in addition to electrostatic, was hydrogen boning, van der Waals force, and their combination, moreover, the assembly guests was diverse with cation/polyanion pair, block polymer micelle and neutral small molecule/polymer complex. This development of assembly method back up the exploration and application of LDHs-based functional composite ultrathin films.

An effective combination of electrodeposition and layer-by-layer assembly to construct composite films with luminescence switching behavior.

This article presents a combination strategy of electrodeposition and a layer-by-layer assembly to fabricate functional composite films with luminescence switching behavior. Firstly, a novel green luminescence film consisting of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HOPTS) was first obtained on ITO by a facile electrodeposition method. Then, the multilayer films containing different layers of tungstophosphate K12.5Na1.5[NaP5W30O110]·15H2O (P5W30) were further fabricated on the green luminescence film to form the composite films [(HOPTS)50/(PDDA/P5W30)n] (n = 10, film 1; n = 27, film 2; n = 57, film 3). Cyclic voltammetry and fluorescence spectroscopy were used to characterize the electrochemical activity of P5W30 and the luminescence property of HOPTS in the composite films, respectively. Lastly, in situ UV-Vis spectroelectrochemical and fluorescence spectroelectrochemical measurements were applied to investigate the luminescence switching behaviors of the composite films controlled by the electrochromism component of P5W30 upon electrochemical modulation. In summary, the investigation results revealed that the electrodeposition method is convenient and rapid, and thus-prepared composite films showed improved luminescence switching performance in terms of switching process, activation cycles, coloration efficiency, and bleached-state transparency as well as good stability, wide voltage range and good reversibility. Therefore, the present study offers a new fabrication route for the multifunctional composite films through an effective combination of electrodeposition and layer-by-layer assembly technique.

General incorporation of diverse components inside metal-organic framework thin films at room temperature.

Porous metal-organic frameworks (MOFs) demonstrate great potential for numerous applications. Although hetero-functional components have been encapsulated within MOF crystalline particles, the uniform incorporation of functional species with different sizes, shapes and functions in MOF thin films with dual properties, especially at room temperature and without the degradation of the MOF framework, remains a significant challenge towards further enriching their functions for various purposes. Here we report a general method that can rapidly encapsulate diverse functional components, including small ions, micrometre-sized particles, inorganic nanoparticles and bioactive proteins, in MOF thin films at room temperature via a metal-hydroxide-nanostrand-assisted confinement technique. These functional component-encapsulated MOF composite thin films exhibit synergistic and size-selective catalytic, bio-electrochemical, conductive and flexible functionalities that are desirable for thin film devices, including catalytic membrane reactors, biosensors and flexible electronic devices.

Homogeneously assembling like-charged WS2 and GO nanosheets lamellar composite films by filtration for highly efficient lithium ion batteries

It is well known that the nanocomponents with opposite charges can be easily assembled into hybrid composites via electrostatic interaction, but it is difficult for like-charged nanomaterials. Here, we developed a general method to directly assemble lamellar composite paper composed of both negative-charged WS2 and graphene oxide (GO) nanosheets from their aqueous dispersion through filtration process. After hydrothermal reduction, the flexible lamellar WS2/reduced-graphene oxide (rGO) paper was evaluated as binder-free anodes for Li-ion batteries, which presented a reversible capacity of 697.7mAhg−1 after 100 cycles, 8 times higher than 88.5mAhg−1 of pure WS2 nanosheets and 60.2mAhg−1 of rGO, excellent cyclic stability and good rate capacity. In the uniformly alternated lamellar structures, rGO nanosheets efficiently prevent the restacking of WS2 sheets, increase the conductivity of the electrode, and sustain the volume expansion during Li+ insertion/extraction, which significantly improved the electrochemical performances. This simple filtration assembling method provides a general and efficient way to synthesize functional composite films from like-charged colloid solutions.

Electrostatic Dry Coating of Cathode Materials for Li ion battery

Organic solvents are widely used in wet coating for manufacturing Li ion batteries. This study focused on switching to environmentally benign solvent-free process, and examined a possibility of electrostatic dry coating (EDC) of cathode materials which are generally composed of active oxides, conductive and binder additives. Firstly, the composite particles containing the three components were prepared by dry mechanical treatment, and then EDC experiment was performed for the composite particles. Interestingly, the composite particles could be tribo-charged enough for electrostatic deposition on an earthed Al foil in air, with relatively high deposition rate. The as-deposited film was further dry-pressed to increase the film density (3 × 103kg/m3). A half cell was assembled using the pressed film as cathode electrode, and it was demonstrated that the initial charge-discharge characteristics were comparable to those obtained for wet-coated films. The results obtained indicate that there are some opportunities for the practical implementation of the EDC method for manufacturing functional composite films.

High catalytic performance of gold nanoparticle–gelatin mesoporous composite thin films

In this paper, Au nanoparticle (NP)–gelatin mesoporous composite thin films were successfully prepared by the formation of Au NPs in the mesoporous gelatin films through in situ reduction of HAuCl4 at room temperature. The mesoporous gelatin films were prepared by using copper hydroxide nanostrands as both the assembling frames and the pore generators. It was found that both the trace aldehyde groups of the glutaraldehyde cross-linker and the reduction groups of gelatin contributed to the formation of Au NPs. The Au NPs were homogeneously formed and dispersed in the gelatin films. The effects of pH and the reduction time on the formation of the Au NPs were investigated in detail. These Au NP–gelatin mesoporous composite films demonstrated superior catalytic properties for the reduction of o-nitroaniline to 1,2-benzenediamine, and several to tens times higher activity than those reported of the Au NP–polymer (or oxide) composites. Similarly, Pt NP–gelatin mesoporous composite films were also prepared. This process is general and simple for other functional composite films.

Photocrosslinkable dextran hydrogel films as substrates for osteoblast and endothelial cell growth

Functional hydrogel films on solid supports are versatile materials with large potential for cell growth and tissue engineering. Here, we report on a modular approach to generate functional hydrogel composite films for endothelial and osteoblast cell co-culture. The polymer network of the parent hydrogel was formed by a dextran derivative (BP-CMD), which contained carboxymethyl (CM) groups for further chemical functionalization and benzophenone (BP) moieties as a photocrosslinkable unit. BP-CMD could be synthesized by three different routes, first with the benzophenone unit attached via an amide bond, or second by an ether bond, or third as an ion pair between the benzophenone ammonium salt and the carboxylate groups on the dextran backbone. For composite formation, BP-functionalized silica nanoparticles, as well as gelatin particles were mixed with BP-CMD and permanently fixed in the hydrogel matrix by photocrosslinking for mechanical reinforcement and to facilitate cell growth. In the last preparation step the BMP-2 growth factor was covalently coupled to the polymer backbone, which enhanced osteoblast and endothelial cell growth. The swelling behavior and successful BMP-2 immobilization of the hydrogel composite films were investigated with surface plasmon resonance and optical waveguide mode spectroscopy coupled with fluorescence detection. This modular approach allows independent selection and optimization of each component in the hydrogel composite for a wide range of potential applications for targeted cell growth, as successfully shown here with osteoblast–endothelial cell co-culture for bone tissue regeneration.

Preparation of a gene-engineering mutant of bacteriorhodopsin BR-D96V and corresponding poly(vinyl alcohol)-based functional composite films

Bacteriorhodopsin (BR) exhibits, as a membrane protein in Halobacterium salinarum, unique photoresponsive behaviors, and shows promise as a functional information material. A new mutant of BR with the 96th aspartic acid replaced by valine (BR-D96V) was obtained and then a composite film of BR-D96V in a synthetic polymer matrix was prepared in this research. The mutant BR-D96V was expressed in a bacterio-opsin deficient halobacterial strain (L33) by gene engineering. Although valine is very hydrophobic, this point mutant keeps the basic biological activities, namely, photoelectric and photochromic responses. Nevertheless, the lifetime of M intermediate in the BR mutant is nearly two orders of magnitude longer than that of wild-type BR in neutral aqueous solution, which benefits its potential application as an information material. The M lifetime is further significantly prolonged after embedding BR-D96V into poly(vinyl alcohol) (PVA). It was also found that BR-D96V is very sensitive to water content in comparison with wild-type BR and another BR mutant.

Rapid Separation and Purification of Nanoparticles in Organic Density Gradients

Nanoseparation and concomitant purification of nanoparticles by ultracentrifugation in a nonhydroxylic organic density gradient has been demonstrated by separating several typical colloidal nanoparticles, including Au, Ag, and CdSe. Successful separation of Au nanowires from their spherical counterparts showed that colloidal particles can be separated not only by size but also morphology. In addition to extending the range of colloidal systems which can be separated and providing monodisperse samples that cannot be obtained by synthesis optimization alone, this method simplifies the postsynthesis treatment process and facilitates subsequent bulk assembly of the monodisperse colloids. Dissolution of organic polymers in the gradient medium both enhances the separation efficiency and also allows the direct fabrication of functional composite films with discrete monodisperse nanoparticles embedded inside.

Polyazetidine-based immobilization of redox proteins for electron-transfer-based biosensors

A highly stable functional composite film was prepared using polyazetidine prepolymer (PAP) with peroxidase from horseradish (HRP) and/or glucose oxidase (GOx). The good permeability of the PAP layer to classical electrochemical mediators, as evaluated by the determination of the diffusion coefficient of different redox molecules, is of great importance in view of the use of PAP as an immobilizing agent in second-generation biosensor development. Cyclic voltammetry of the HRP–PAP layer on a glassy carbon electrode (GCE) showed a pair of stable and quasi-reversible peaks for the HRP–Fe (III)/Fe (II) redox couple at about −370 mV vs. Ag/AgCl electrode in pH 6.5 phosphate buffer. The electrochemical reaction of HRP entrapped in the PAP film exhibited a surface-controlled electrode process. This film and the successive modifications (HRP–PAP self-assembled monolayer (SAM) modified Au electrode) were used as a biological catalyst (hydrogen peroxide transducers) for glucose biosensors, after coupling to GOx. Both HRP/GOx–PAP and HRP/GOx–PAP SAM third generation biosensors were prepared and characterized. The use of PAP as immobilizing agent offers a biocompatible micro-environment for confining the enzyme and foreshadows the great potentiality of this immobilizing agent not only in theoretical studies on protein direct electron transfer but also from an applications point of view in the development of second- and third-generation biosensors.

Preparation, characterization, and electrocatalytic activity of Prussian blue/poly(N‐acetylaniline) composite film

AbstractElectrochemical preparation of the Prussian blue (PB)/poly (N‐acetylaniline) (PNAANI) composite film was carried out by cyclic voltammetry (CV). Its surface morphology, which was evaluated by Atom Force Microscope (AFM), revealed that PNAANI film provides lots of redox centers for PB growth so that the electrodeposition of PB showed high current densities, and the composite film is much denser than pure PB film. The surface microstructure of the composite film was also characterized by X‐ray photoelectron spectrum (XPS). Due to the existence of electrostatic interaction between the PNAANI (polycation) film and the PB (polyanion) film, the composite film cannot be considered as a simple adherent bilayer of PB film and PNAANI film. The electroactivity and stability of the PB/PNAANI composite film in acidic electrolytes containing potassium ions were comparatively higher than that of the pure PB film. The functional composite film is expected for use in the system capable of effective accumulation of charge, and for the analytical applications towards the reduction of hydrogen peroxide due to its high electrocatalytic activity. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Composite films of lecithin and heme proteins with electrochemical and electrocatalytic activities

Functional composite films made from lecithin micelles and the two heme proteins of met-myoglobin (Mb) and met-hemoglobin (Hb) are reported in this paper. Proteins in functional composite films have much higher rates of electron transfer than proteins in solutions on carbon paste (CP) electrodes. Cyclic voltammograms (CVs) all give a pair of well-defined and quasi-reversible peaks, corresponding to the heme FeIII/FeII redox couple of proteins. Differential pulse voltammograms (DPVs) also show the same formal potential (E0') values of proteins under identical conditions. Electronic and vibrational spectra indicate that proteins in these films are not denatured, but their conformational differences from native states may exist. The E0' value for Mb in the lecithin film is found to be pH dependent. The Mb lecithin film can catalytically reduce O2 and H2O2, and its analytical application to H2O2 determination is established.

Novel amperometric biosensor based on composite film assembled by polyelectrolyte-surfactant polymer, carbon nanotubes and hemoglobin

A novel hydrogen peroxide biosensor has been developed based on the encapsulation of hemoglobin (Hb) in the composite film of carboxylic carbon nanotubes and polyelectrolyte-surfactant polymer. The direct electron transfer of the Hb entrapped in the composite film was observed. The formal potential of the encapsulated Hb was −0.287 V versus SCE and the heterogeneous electron transfer rate constant was 0.4 s −1 in a 0.1 M phosphate buffer solution (pH 7.0). An FT-IR spectroscopy study confirms that the secondary structure of Hb encapsulated in the composite film still retains the original arrangement. It is suggested that the achieved faradic response of the hemoglobin be due to the promotion properties of carbon nanotube in electron transfer in biomembrane-like polyelectrolyte-surfactant polymer. The entrapped Hb exhibited excellent electrocatalytic activity to reduce hydrogen peroxide. The properties of functional composite film, together with the bioelectrochemical catalytic activity, could make them useful in the development of bioelectronic devices and investigation of protein electrochemistry at functional interface.

Multicomponent Patterning of Layer‐by‐Layer Assembled Polyelectrolyte/Nanoparticle Composite Thin Films with Controlled Alignment

Composite thin films of polyelectrolytes and fluorescent nanoparticles can be directly transfer-printed onto various substrates including indium tin oxide coated poly(ethylene terephthalate). The sequential transfer printing of thin films with controlled alignment introduces multicomponent patterns onto substrates, demonstrating possible practical device fabrication using functional polyelectrolyte multilayer composite thin films (see Figure).