Increase In Number Of Bilayers Research Articles

Effect of bilayer numbers on structural, mechanical, tribological and corrosion properties of TiO2–SiO2 multilayer film-coated β-type Ti45Nb alloys

Protective films with excellent tribological performance and good corrosion resistance are needed in general because titanium implants are used in aggressive environments and always suffer from severe wear and corrosion. In this study, TiO2–SiO2 multilayer films were deposited with different numbers of bilayers (2, 4, and 8) on β-type Ti45Nb alloy substrates by physical vapour deposition. The influence of number of bilayers on microstructure, wettability, mechanical features, tribological performance and electrochemical behaviour of TiO2–SiO2 multilayer films were comparatively observed via XRD, XPS, SEM, AFM, nanoindentation tester, contact angle measurement system, reciprocating tribo-tester, and electrochemical corrosion media. The surface hardness, wear and corrosion resistance values of multilayer film-coated substrates were higher than the untreated substrate values. These properties and adhesion resistance and hydrophobicity of coated samples also increased with increase in number of bilayers due to the smaller grain size, increased layered interfaces and high structural density.

Construction phosphorus/nitrogen-containing flame-retardant and hydrophobic coating toward cotton fabric via layer-by-layer assembly

Excellent flame-retardant cotton fabric with desired hydrophobic is of particular interests for both academia and industry. Herein, an effective multilayer coating consisting of phosphorylated polyethyleneimine (P-PEI) and hydrophobic modified ammonium polyphosphate (MAPP) was successfully constructed on cotton fabric through a facile layer-by-layer (LbL) assembly, which imparted high fire retardancy and desirable hydrophobic to the cotton fabric. Coated cotton fabric was characterized by Fourier infrared spectrometer, scanning electronic microscopy coupled with its energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy, conforming that a phosphorus- and nitrogen-containing multilayer coating was homogeneous and uniform increase on the surface of cotton fabric. The resultant cotton fabric achieved self-extinguishing in vertical burning tests and a desired hydrophobic with a water contact angle of 127.4° with only 4BL coating. Moreover, the coated cotton fabrics exhibited a slight delay of ignition accompanied by remarkably decrease of heat release and the fire growth rate index, suggesting the outstanding fire safety. The flame retardancy of coated cotton fabric was enhanced and even not ignited at the heat flux of 25 kW/m2, but the hydrophobic was almost not changed with the increase of bilayer number. Additionally, the relevant analysis of residues and volatile gases manifested that the multilayer coating contributed flame-retardant activities in both condensed- and gas-phase via forming thermally stable char residues and inhibiting the release of flammable gases. Taking advantage of the features, this high efficiency coating together with the facile finishing technique would have great potentials in application of multifunctional cotton fabrics.

Evolution of the interface microstructure of short-period Cr/Ti multilayers with increase in number of bi-layers

Evolution of interface microstructure with addition of more number of layers has been investigated on Cr/Ti multilayer which is important for application as a mirror or monochromator in the “water window” soft X-ray spectral regime. Two sets of Cr/Ti multilayers at moderate and low bi-layer thickness regime have been prepared for this purpose using Ion Beam Sputtering technique. In one set, Cr/Ti multilayer with 25, 50, 60 and 100 numbers of bilayers with moderate bi-layer thickness of 3.8 nm have been deposited. In another set, four samples each having low bilayer thickness of 2.4 nm with 25, 50, 75 and 100 number of bi-layers have been prepared and the multilayers have subsequently been characterized with Specular X-ray reflectivity and diffuse X-ray scattering measurements at grazing incidence with hard X-rays. It is observed that cumulative effect of interface imperfections became more pronounced with increasing number of bilayers resulting in continuous increase in the interface width in both the thickness regimes; however, its evolution is not exactly same for the two sets of samples. Diffuse X-ray scattering result reveals that for the first set of samples, interface imperfections are dominated by interface roughness with no change in the interface diffusion with increase in number of layers, while for the second set, both interface roughness as well as interface diffusion contribute towards the cumulative accumulation of interface imperfections which is also confirmed by cross-sectional Transmission Electron Microscopy. Finally, performance of the multilayers in water window regime has been checked by soft X-ray reflectivity measurements using synchrotron radiation. The above results have direct implication in utilisation of these multilayers over a wide bi-layer thickness regime required to cover the full ‘water-window’ spectrum.

Transport studies of ionic solutes through chitosan/chondroitin sulfate A (CHI/CS) polyelectrolyte multilayer membranes

Nano scale assembling has led to the capability to directly control and enhance the capabilities and properties of a material through change of its structural makeup at the nano scale. A novel class of functional layers in which various properties can be tunable via in situ modifications of nanostructure through stimuli such as pH, capping, and salt addition provides a promising strategy to develop polyion responsive polyelectrolyte multilayer membranes (PEM’s). The concentration (diffusion dialysis) and pressure dependent (ultrafiltration) studies of solution containing polyvalent ions through the chitosan/chondroitin sulfate A (CHI/CS) multilayers fabricated on ultipore membrane have been studied. The characterization of the bilayer pair was done with analytical instruments like ATR-FTIR, spectroscopic ellipsometry, SEM, AFM and finally TGA for water holding capacity. The characterization of bilayer pairs demonstrated the stability and integrity of bilayer pair. An important bilayer property such as water holding capacity and ion permeability across it was examined and a positive correlation was found with increase in number of bilayers. The possibility of capping a fabricated bilayer with another polyelectrolyte, polyethylene glycol (PEG) was used to examine the extend of efficiency. The permeation rate of ions across bilayers increased with makeup salt concentration was observed with capping. An increase in selectivity was observed with increase in the number of bilayers for Na+/Cu2+, Na+/Ag+ and Na+/Mn3+. 12.5 hybrid CHI/CS-PEG membranes shows a selectivity of 38.52 for Cl−/PO43− with a permeation rate of 37.54 × 10–5 cms−1 and 4.23 × 10–5 cms−1 respectively for Cl− and PO43−. The transport profile of a model vitamin, ascorbic acid (AA) through CHI/CS multilayers showed the capability of bilayer membrane for selective solute transport.

Optically Active Multilayer Films Based on Chitosan and an Azopolymer

The layer-by-layer technique has been widely adopted for the fabrication of nanostructures with tailored properties. In this work, photoactive multilayer films consisting of alternating layers of chitosan and an azopolymer were developed by this method. Taking into account that pH is the factor controlling the charge of weak polyelectrolytes, the influence of this parameter on the structure and properties of the multilayer films was evaluated. Thus, different films were prepared by varying pH conditions as well as bilayer number. The morphology and properties of the films were analyzed by diverse advanced techniques, such as ultraviolet-visible spectroscopy, X-ray diffraction, and atomic force microscopy equipped with PeakForce QNM (Quantitative Nanomechanical Property Mapping). It was found that the thickness, roughness and elastic modulus of the developed multilayer films increased with the decrease of the chitosan solution pH and the increase of the bilayer number. Furthermore, induced birefringence measurements revealed that a higher level of photo-orientation was attained with the decrease of pH and the increase of bilayer number.

LbL Fabricated Poly(Styrene Sulfonate)/TiO2Multilayer Thin Films for Environmental Applications

Fabrication of multilayer ultrathin composite films composed of nanosized titanium dioxide particles (P25, Degussa) and polyelectrolytes (PELs), such as poly(allyl amine hydrochloride) (PAH) and poly(styrene sulfonate sodium salt) (PSS), on glass substrates using the layer-by-layer (LbL) assembly technique and its potential application for the photodegradation of rhodamine B under ultraviolet (UV) irradiation has been reported. The polyelectrolytes and TiO(2) were deposited on glass substrates at pH 2.5 and the growth of the multilayers was studied using UV/vis spectrophotometer. Thickness measurements of the films showed a linear increase in film thickness with increase in number of bilayers. The surface microstructure of the thin films was characterized by field emission scanning electron microscope. The ability of the catalysts immobilized by this technique was compared with TiO(2) films prepared by drop casting and spin coating methods. Comparison has been made in terms of film stability and photodegradation of rhodamine B. Process variables such as the effect of surface area of the multilayers, number of bilayers, and initial dye concentration on photodegradation of rhodamine B were studied. Degradation efficiency increased with increase in number of catalysts (total surface area) and bilayers. Kinetics analysis indicated that the photodegradation rates follow first order kinetics. Under maximum loading of TiO(2), with five catalyst slides having 20 bilayers of polyelectrolyte/TiO(2) on each, 100 mL of 10 mg/L dye solution could be degraded completely in 4 h. The same slides could be reused with the same efficiency for several cycles. This study demonstrates that nanoparticles can be used in wastewater treatment using a simple immobilization technique. This makes the process an attractive option for scale up.

Assembly of Electroactive Layer-by-Layer Films of Myoglobin and Ionomer Poly(ester Sulfonic Acid)

Layer-by-layer films were assembled on solid substrates by alternate adsorption of negatively charged ionomer poly(ester sulfonic acid) or Eastman AQ55 from its aqueous dispersion and positively charged myoglobin (Mb) from its solution at pH 4.5. The film assembly process was monitored by cyclic voltammetry (CV), UV–vis spectroscopy, and quartz crystal microbalance (QCM). {AQ/Mb} n films grown on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible CV peaks at about −0.20 V vs Ag/AgCl in pH 5.5 buffers, characteristic of the Mb heme Fe(III)/Fe(II) redox couple. Although the amount of Mb adsorbed in each bilayer was essentially the same, the fraction of electroactive Mb decreased dramatically with an increase of bilayer number ( n). Soret absorption bands of {AQ/Mb} n films on glass slides suggest that Mb in the films retains its native state in the medium pH range. Trichloroacetic acid, oxygen, and hydrogen peroxide were electrochemically catalyzed by {AQ/Mb} 6 films with significant lowering of reduction overpotential.

Fluorescence Quenching Based Thin Film Sensors Employing Electrostatic Layer-by-Layer Self-Assembly

ABSTRACTIn this work, the fabrication and performance of thin film optical chemical sensors based on the fluorescence quenching of indicator molecules by several analytes such as organic nitro compounds or metal ions are described. To fabricate the sensors, a fluorescent molecule, 1- hydroxypyrene-3,6,8-trisulfonate or pyrene methanol, was covalently incorporated into poly(acrylic acid) (PAA) and subsequently the polymers were assembled with a polycation employing electrostatic layer-by-layer self-assembly into thin film structures. Fluorescence intensities decreased with increasing concentration of analytes. Quenching behavior follows Stern-Volmer bimolecular quenching kinetics. Linear increase in absorbance, film thickness and emission intensity was observed with increase in number of bilayers deposited in all multilayer films.