Electrostatic Deposition Research Articles

Long-period fiber grating moisture sensor with nano-structured coatings for structural health monitoring

In this article, we inscribe long-period gratings on an SMF-28 optical fiber by a focused CO2 laser beam to develop a humidity sensor with high sensitivity and selectivity for moisture detection for civil infrastructures health monitoring. We propose two types of nano-structured film to deposit on surface of the grating region by electrostatic self-assembly deposition process. The primary nanofilm coating (PAH+/PAA−) does not affect long-period grating properties such as resonance wavelength and transmission intensity; however, it increases the sensitivity by changing the refractive index of the surrounding analytes. The secondary nanofilm coating (Al2O3+/PSS−), due to its molecule structure compatibility, can selectively adsorb analyte molecules of interest (in this case H2O only). The experimental results reveal that the nanofilm-coated long-period gratings are more sensitive to moisture in terms of both wavelength shift and resonance intensity change as of 0.019%/pm and 0.01%/10−3 dBm, respectively, while the bare LPG coefficients are 0.021%/pm and 0.0603%/10−3 dBm. The proposed sensor shows excellent thermal stability as well.

Effect of preparation methods on activation of cobalt catalyst supported on silica fiber for Fischer–Tropsch synthesis

Silica fibers (SF) have been synthesized by facile combination of a sol–gel method and electrospinning technique and investigated as supports of cobalt catalysts for Fischer–Tropsch synthesis (FTS). Tetraethyl orthosilicate (TEOS) was used as precursors for the production of silica fibers. The cobalt supported on silica fibers (Co/SF) catalysts were prepared with the impregnation (IM), strong electrostatic adsorption (SEA), deposition precipitation (DP), and hydrothermal synthesis (HT) method and characterized by N2 adsorption, SEM, TEM, XRD, EDX, H2-TPR and H2-chemisorption. The results showed that the preparation methods significant affected the catalytic activity of Co/SF catalyst. The catalyst prepared by the SEA method showed the highest catalytic activity for FTS reaction, and their catalytic activities were varied in the order of SEA>DP>IM≫HT. The XRD analysis showed that the Co3O4 particles on the Co/SF catalyst prepared by SEA method (9nm) were smaller than those on catalyst prepared by IM method (30nm). The size of the Co3O4 particles was controlled by the preparation method, with small particles formed in catalyst prepared by SEA, DP and HT method. The excellent catalytic activity of Co/SF-SEA may be attributed to the smaller size of cobalt particles and higher cobalt dispersion on this catalyst.

Electrostatic deposition of silica nanoparticles between E‐glass fibers and an epoxy resin

ABSTRACTThe achievement of optimum adhesion between a thermoset and an inorganic material is an important goal for the composites and coatings industries. There is a growing interest in the use of structural surface modifiers, such as nanotubes, nanoparticles, and whiskers, to improve this adhesion. Here, a method for electrostatically depositing poly(ethylene imine)‐functionalized silica nanoparticles onto E‐glass fibers was developed. The deposition of 26‐nm functionalized particles onto glycidyloxypropyltrimethoxysilane (GPS)‐functionalized E‐glass fibers and then their embedding in a resin of diglycidyl ether of bisphenol A and m‐phenylene diamine increased the interfacial shear strength (IFSS) 35% over that of bare fibers and 8% over that of GPS‐functionalized fibers. IFSS was highly dependent on the particle size; the 16‐nm functionalized particles had little effect on the IFSS. When the particles size was increased to 71 and 100 nm, this led to increasingly poor IFSS values, whereas the 26‐nm particles produced the best results. Similar results were seen with the transverse flexural strength of the unidirectional composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41516.

Influence of environmental stresses on the physicochemical stability of orange oil bilayer emulsions coated by lactoferrin–soybean soluble polysaccharides and lactoferrin–beet pectin

Based on layer-by-layer electrostatic deposition, orange oil bilayer emulsions stabilized with lactoferrin (LF)–soybean soluble polysaccharides (SSPS) and lactoferrin (LF)–beet pectin (BP) were prepared. The effect of environmental stresses (ionic strength, pH, freeze–thaw and light) on the physicochemical stability of primary and secondary emulsions was investigated. In the absence of anionic polysaccharides, orange oil emulsion was highly unstable and aggregated at pH7–9 and NaCl of 0.1–0.5M. The droplets in LF–SSPS coated emulsion were stable against aggregation at pH range of 3–10 and NaCl concentration less than 0.3M, while the droplets in LF–BP coated emulsion were stable against aggregation at pH4–9 and NaCl concentrations of 0–0.5M. All the primary and secondary emulsions showed the instability after the freeze–thaw treatment and the stability could be improved in the presence of maltodextrin. During the light exposure (0.35W/m2, 45°C) for 8h, the bilayer emulsions could protect key volatile compounds (decanal, octanal and geranial) from the oxidation compared with the primary emulsions. These results suggested that the layer-by-layer electrostatic deposition could improve the stability of LF-coated emulsion to environmental stresses.

Antistatic Composite Coаtings on the Basis of Powder Paints

For operating under outer space conditions besides providing originally specified protective function, coating should often ensure accomplishment of functional properties, for instance conductivity of electric current. The solution of this problem can be reached by adding powder fillers with specified functional properties into powder paint. The paper deals with development of technique for formation of protective conducting coatings by filling powder paints and treatment in planetary ball mill. For protection of magnesium alloy shells the technique is offered which combines formation of the oxidized sublayer, introduction of electroconductive filler, treatment of the powder mixture in the planetary ball mill and electrostatic deposition of sifted mixture of definite dispersion. This allows sinking of static electricity from cabinets of the equipment for the space-crafts applications in conditions of the outer space.

Superhydrophobic polymeric coatings produced by rapid expansion of supercritical solutions combined with electrostatic deposition (RESS-ED)

In this paper we present a method to produce superhydrophobic polymeric coatings by combining the rapid expansion of supercritical solutions (RESS) with electrostatic deposition (ED). A copolymer, poly(vinyl acetate)–poly(vinyl pivalate) was dissolved in a mixture of supercritical carbon dioxide and acetone and sprayed through a nozzle with an applied voltage of 8kV onto a surface placed on a earthed collector. Spray distance and polymer concentration were altered to find the most suitable spraying conditions. Superhydrophobic surfaces were produced when spraying both with and without a voltage, although the water repellent surfaces could be produced at a larger variety of processing parameters using the RESS-ED technique. The greatest improvement of using the RESS-ED process was that larger and thinner coatings were produced with a more even surface coverage of the created polymer particles compared to spraying without the applied voltage.

Fabrication of biopolymer nanoparticles by antisolvent precipitation and electrostatic deposition: Zein-alginate core/shell nanoparticles

Core-shell biopolymer nanoparticles were prepared using antisolvent precipitation to form surfactant-stabilized zein core nanoparticles and then electrostatic deposition to form an alginate shell. The particle yield was relatively high (95%). The nanoparticles had a core diameter of about 80 nm, a shell thickness of about 40 nm, and an electrical charge of about −21 mV (pH 4.0). The amount of alginate required to saturate the surfaces of the zein nanoparticles was 2.0 mg/m2. The nanoparticle suspensions had relatively good stability to pH: the particles were stable to aggregation from pH 3 to 8, but aggregated at pH 2 due to loss of charge. They were also relatively stable to elevated ionic strengths: the particles were stable to aggregation up to 100 mM NaCl at pH 7.0 and up to 2.0 M NaCl at pH 4.0. The suspensions had good thermal stability at pH 7, i.e., no increase in particle size after heating at 90 °C for 120 min. Nevertheless, some particle growth was observed during heating at pH 4 for 2 h. The core/shell biopolymer nanoparticles fabricated in this study have potential to be used as nano-delivery systems for bioactive molecules in food and pharmaceutical formulations.

Fabrication and characterization of kesterite Cu2ZnSnS4thin films deposited by electrostatic spray assisted vapour deposition method

Most of the high efficiency kesterite solar cells are fabricated by vacuum or hydrazine-based solution methods which have drawbacks, such as high cost, high toxicity or explosivity. In our contribution, an alternative non-vacuum and environmental friendly deposition technology called electrostatic spray assisted vapour deposition (ESAVD) has been used for the cost-effective growth of Cu2ZnSnS4 (CZTS) thin films with well controlled structure and composition. CZTS films have been characterized using a combination of XRD, XPS, SEM-EDX, AFM, and Raman spectroscopy. The results demonstrated that adherent, uniform and homogeneous CZTS films without apparent secondary phases have been produced by ESAVD. The atomic ratios measured by EDX are Cu/(Zn + Sn) = 0.88 and Zn/Sn = 1.17,which are very close with the reported high efficiency solar cells and can be finely tuned by formulating the precursor.CZTS films exhibited a typical optical band gap of 1.53 eV from UV–Vis analysis. Cu2ZnSnS4 produced by the ESAVD are being optimized towards the fabrication of high efficiency photovoltaic devices.

Effect of SAM Chain Length on Mediated Amperometric Detection of Glucose

Self-assembled monolayers with reactive terminal functionality are frequently used for constructing chemical sensors. The sensors can subsequently be modified by covalent attachment or electrostatic deposition of other materials to introduce specificity at the surface for the sensing application. Electrostatic deposition is a simple method used to build structures at an interface, and is a method that can be easily adapted for biological molecules (e.g. proteins, enzymes, etc.) without compromising the integrity of the protein/enzyme. When depositing biological molecules, however, the chain length can affect the kinetics of the glucose oxidase/glucose reaction. This research used cyclic voltammetry to measure the Michaelis-Menton kinetics of the glucose oxidase reaction with glucose in the presence of a mediator. The Michaelis-Menton kinetics were measured using three different thiols of varying lengths. The length of the chain was shown to have an effect where the shortest chain had significantly different kinetics compared to the longer chains.

An alternative non-vacuum and low cost ESAVD method for the deposition of Cu(In,Ga)Se2 absorber layers

In this article, an environmentally friendly and non-vacuum electrostatic spray assisted vapor deposition (ESAVD) process has been developed as an alternative and low cost method to deposit CIGS absorber layers. ESAVD is a non-vacuum chemical vapor deposition based process whereby a mixture of chemical precursors is atomized to form aerosol. The aerosol is charged and directed towards a heated substrate where it would undergo decomposition and chemical reaction to deposit a stable solid film onto the substrate. A sol containing copper, indium, and gallium salts, as well as thiourea was formulated into a homogeneous chemical precursor mixture for the deposition of CIGS films. After selenization, both XRD and Raman results show the presence of the characteristic peaks of CIGSSe in the fabricated thin films. From SEM images and XRF results, it can be seen that the deposited absorbers are promising for good performance solar cells. The fabricated solar cell with a typical structure of glass/Mo/CIGSSe/CdS/i-ZnO/ITO shows efficiency of 2.82% under 100 mW cm−2 AM1.5 illumination.

Gelatin-Chitosan Composite Films and Edible Coatings to Enhance the Quality of Food Products: Layer-by-Layer vs. Blended Formulations

Two different approaches, blending and layer-by-layer electrostatic deposition (LbL), were utilized to combine two biopolymers, gelatin and chitosan, in edible films or coatings. The performance of the blended and LbL composite films and single-component gelatin and chitosan films was compared in terms of mechanical, optical, and spectroscopic properties. In parallel, edible coatings based on these formulations were applied on a food model: fresh-cut melon. Physiological, textural, and microbiological parameters of the coated fruit were studied in comparison with non coated control. Surprisingly, in spite of the higher thickness, the composite films and especially the LbL formulation demonstrated enhanced water vapor permeability as compared to single-component films. The LbL film had higher strength and better elasticity than the blended one. All edible coatings containing chitosan effectively inhibited microbial growth on fresh-cut melons. The LbL formulation demonstrated the most effective inhibition of the total microbial growth especially after 5–7 days of storage, while the blended formulation demonstrated high antifungal activity after 11 days of storage. The LbL formulation demonstrated superior performance in preservation of fruit texture and also slightly reduced fruit weight loss, while the blended formulation did not improve these parameters. Both composite coatings do not obstruct fruit gas exchange and do not cause accumulation of off-flavor volatiles.

Hofmeister Salts Affect Buildup of Thin Multilayer Films Surrounding Oil Droplets

The layer-by-layer electrostatic deposition method is a novel technique to precisely control the interfacial properties of multilayered films such as charge, thickness, permeability, and composition. The formation and stability of multilayered emulsions is however often plagued by extensive droplet flocculation and aggregation even at ideal polyelectrolyte concentrations where saturation should occur. Addition of salts may reduce the degree of attractive interactions ions and thus improve deposition. To test this hypothesis, the influence of different Hofmeister salts (KCl, NaCl, LiCl, and NH4Cl) at various salt concentrations (0–2500 mM) on the aggregation behavior of multilayered emulsions was investigated. A simple coating process of fish gelatin interfacial membranes with sugar beet pectin was used. Our results show that mean particle diameter and particle size distribution of emulsions initially decreased from 600 nm to 328 nm with increasing salt concentrations up to 250 mM. Above a critical level (>500 mM), heavy aggregation of emulsions at the presence of chaotropic salts occurred whereas kosmotropes reduced flocculation and creaming. Microscopic images and isothermal titration calorimetry confirmed particle size measurements. Results thus suggest that addition of salts may be an extremely useful tool to modulate and improve depositioning of alternatingly charged polymers on surfaces.

Electrochemical performance of continuously gradient composite cathode fabricated by electro-static slurry spray deposition

The cobalt-based cathode, LSCF, BSCF and SSC, have high thermal expansion coefficients, which cause poor thermal compatibility with electrolytes and limited cell performance. In this work, a continuously gradient Sm0.5Sr0.5CoO3−δ (SSC) – BaCe0.7Zr0.2Y0.1O3−δ (BCZY) composite cathode was developed for BCZY electrolyte based fuel cells by electrostatic spray slurry deposition (ESSD). In the deposited cathode the content of BCZY gradually decreased and that of SSC gradually increased in the direction away from the electrolyte–cathode interface. The single cell, consisting of a BCZY–NiO anode substrate, a BCZY electrolyte and a compositionally gradient SSC-BCZY cathode layer, was assembled and tested from 550 to 700 °C under humidified hydrogen atmosphere (∼3% H2O) and static air as an oxidant. The cross-sectional morphology of the cathode was examined by energy dispersive X-ray (EDX) analysis. The comparison of electrochemical performances between various cathode configurations was conducted to demonstrate the effect of gradient cathode. The power density and impedance spectra indicate that the optimized cathode structure greatly improves the polarization resistance and ohmic resistance. The results suggest that the migration of protons to triple phase boundaries (TPBs) and the surface diffusion of O− might be enhanced in the gradient SSC–BCZY composite cathodes.

Wet-chemical enzymatic preparation and characterization of ultrathin gold-decorated single glass nanopore.

The conical glass nanopore was modified through layer-by-layer electrostatic deposition of a monolayer of glucose oxidase, and then an ultrathin gold film was formed in situ through enzyme-catalyzed reactions. The morphology and components of single glass nanopore before and after ultrathin Au deposition were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis, respectively. In particular, the quenching of the quantum dots fluorescence in the nanopore tip zone further illustrated that the gold nanofilm was successfully deposited on the inner wall of the single glass nanopore. The Au thin films make the glass nanopores more biologically friendly and allow the nanopores facile functionalization of the surface through the Au-S bonds. For instance, the ionic current rectification (ICR) properties of the gold-decorated glass nanopores could be switched readily at different pHs by introducing different thiol molecules.

Microgel-modified surfaces enhance short-term osteoblast response

Modulations of surface structure or chemistry over various length scales are able to control the interactions of cells with biomaterials surfaces. This effect has been extensively studied using a number of top-down lithographic patterning processes. We create a modulated surface using a simple, bottom-up, self-assembly method involving the electrostatic deposition of microgels onto surfaces. We copolymerize acrylic acid (AA) with poly(ethylene glycol) (PEG) by suspension polymerization to form negatively charged, submicron-sized PEG-AA microgels and electrostatically deposit these onto cationic poly-l-lysine (PLL) primed substrates. The PEG-AA microgels resist fibronectin adsorption while the exposed PLL between adjacent microgels adsorbs fibronectin, thus producing a disordered array of submicron sized non-adhesive features separated from each other by microscale distances on an otherwise cell-adhesive surface. Relative to continuously adhesive surfaces, microgel-modulated adhesiveness increases both short-term cell spreading and cell proliferation (MTS) while maintaining the same differentiation behavior (ALP). Scanning electron microscopy indicates that osteoblasts grow over the microgels while adhering to the exposed adhesive surface between the microgels. Time-resolved optical microscopy shows that microgel-modified surfaces induce higher cell motility than the unmodified controls. These findings are consistent with the idea that cell–surface interactions are regulated by the spatial distribution of cell-adhesive sites on a surface, and they furthermore suggest a simple method by which to influence cellular processes associated with healing after the implantation of a tissue-contacting biomedical device.

Time course of bronchial cell inflammation following exposure to diesel particulate matter using a modified EAVES

Electrostatic deposition of particles onto the surface of well-differentiated airway cells is a rapid and efficient means to screen for toxicity associated with exposure to fine and ultrafine particulate air pollution. This work describes the development and application of an electrostatic aerosol in vitro exposure system (EAVES) with increased throughput and ease-of-use. The modified EAVES accommodates standard tissue culture plates and uses an alternating electric field to deposit a net neutral charge of aerosol onto air-interface cell cultures. Using this higher-throughput design, we were able to examine the time-course (1, 3, 6, 9, and 24h post-exposure) of transcript production and cytotoxicity in well-differentiated human bronchial cells exposed to diesel particulate matter at levels of ‘real-world’ significance. Statistically significant responses were observed at exposure levels (∼0.4μg/cm2) much lower than typically reported in vitro using traditional submerged/resuspended techniques. Levels of HO-1, IL-8, CYP1A1, COX-2, and HSP-70 transcripts increased immediately following diesel particulate exposure and persisted for several hours; cytotoxicity was increased at 24h. The modified EAVES provides a platform for higher throughput, more efficient and representative testing of aerosol toxicity in vitro.

Preparation and characterization of micropatterned prussian blue thin films with enhanced electrochromic properties

Micropatterned prussian blue thin films on indium tin oxide conducting glass were prepared by electrostatic field-assisted potentiostatic deposition and their electrochromic properties were investigated in this study. Scanning electron microscope and optical microscope images confirmed the formation of micropatterned prussian blue thin films. Cyclic voltammetry, double-potential-step experiments and UV–Vis absorbance spectra were performed to evaluate the electrochromic performance of the thin films. It is found that the coloration efficiency and the coloring/bleaching response times of the mPB thin films were faster than that of the PB thin films without micropatterns.

New biomaterial based on cotton with incorporated Biomolecules

ABSTRACTThe aim of this study was to investigate a method of embedding l‐cysteine (l‐cys), an antimicrobial agent, between layers of chitosan (CH) and sodium alginate (ALG) onto cotton samples obtained via a layer‐by‐layer electrostatic deposition technique via several embedding methods. The results show that the best way to incorporate l‐cys into the layers was the one that used the property of gelling ALG. To monitor the l‐cys embedding into the CH/ALG multilayer film, different methods were used: energy‐dispersive X‐ray spectrometry analysis to assess the presence of sulfur on the sample, Ellman's reagent method to analyze l‐cys release from the sample, and attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (FTIR) to compare the ATR–FTIR spectra of the pure l‐cys and l‐cys embedded in the CH/ALG multilayer film to study the interaction between the l‐cys and the CH/ALG multilayer films. Functionalized CH/ALG cotton samples were also investigated for their antibacterial properties toward Staphylococcus aureus and Klebsiella pneumonia with the Japanese Industrial Standard method JIS L 1902:2002, and the results show an enhancement of the antibacterial effect due to the presence of l‐cys. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40519.

Responsiveness of emulsions stabilized by lactoferrin nano-particles to simulated intestinal conditions

There is an upsurge of interest in the use of nano-particles to fabricate emulsions and modulate their functionality, with particular emphasis on modulating emulsion digestive fate. Food grade nano-particles formed through controlled processing and electrostatic biopolymer interactions are yet to be systematically studied for their ability to stabilize emulsions and modulate emulsion digestibility. This study focused on the responsiveness of emulsions stabilized by lactoferrin (LF) nano-particles (NPs) and dietary fibers to key digestive parameters. Compared to native LF, LF-NPs comprised emulsion exhibited elevated creaming rates as evident from accelerated stability tests performed by analytical centrifugation. The electrostatic deposition of alginate or carrageenan onto the LF-NPs significantly improved the stability of the corresponding emulsions. Further, the use of various nano-particles showed to have both beneficial and deleterious effects on emulsion responsiveness to pH (2.0 < pH < 10.0), CaCl2 (0-40 mM) and bile (0-25 mg mL(-1)). Simulated pH-stat lipolysis experiments show that the use of LF or LF-NPs had no marked effect on lipolysis. Intriguingly, the use of LF-NPs and alginate reduced emulsion lipolysis by 14% while the use of LF-NPs and carrageenan increased lipolysis by 10%. Microscopy images as well as droplet characterization in terms of size and charge indicate that the altered emulsion responsiveness may be due to physical differences in emulsion properties (e.g. droplet size) and overall organization during digestion (e.g. aggregation vs. coalescence). Overall, this study's insights could prospectively be used to harness protein nano-particles to tweak emulsion behavior during digestion.

Combinatorial scaffold morphologies for zonal articular cartilage engineering

Articular cartilage lesions are a particular challenge for regenerative medicine strategies as cartilage function stems from a complex depth-dependent organization. Tissue engineering scaffolds that vary in morphology and function offer a template for zone-specific cartilage extracellular matrix (ECM) production and mechanical properties. We fabricated multi-zone cartilage scaffolds by the electrostatic deposition of polymer microfibres onto particulate-templated scaffolds produced with 0.03 or 1.0mm3 porogens. The scaffolds allowed ample space for chondrocyte ECM production within the bulk while also mimicking the structural organization and functional interface of cartilage’s superficial zone. Addition of aligned fibre membranes enhanced the mechanical and surface properties of particulate-templated scaffolds. Zonal analysis of scaffolds demonstrated region-specific variations in chondrocyte number, sulfated GAG-rich ECM, and chondrocytic gene expression. Specifically, smaller porogens (0.03mm3) yielded significantly higher sGAG accumulation and aggrecan gene expression. Our results demonstrate that bilayered scaffolds mimic some key structural characteristics of native cartilage, support in vitro cartilage formation, and have superior features to homogeneous particulate-templated scaffolds. We propose that these scaffolds offer promise for regenerative medicine strategies to repair articular cartilage lesions.