Dip-coating Times Research Articles

Achieving broadband microwave absorption and excellent mechanical properties via constructing 3D reduced graphene oxide networks in glass fiber/epoxy resin composites

The rapid development of electronic information technology makes it more urgent that explore high-efficiency microwave absorption materials to cope with the challenges of electromagnetic pollution for guarding information security and human health. Herein, we prepared functional composites with both broadband microwave absorption and excellent mechanical properties via constructing three-dimensional (3D) reduced graphene oxide (RGO) networks. In these composites, glass fibers (GFs) were uniformly coated by RGO through a straightforwardly feasible repeated dip-coating process and subsequent reduction, which were named (RGO)n@GF (n was dip-coating times). The GFs supported RGO to form 3D networks, which increased the transmission paths and multiple scattering of electromagnetic waves. Meanwhile, the networks improved the electrical conductivity and conduction loss. The results show that the (RGO)10@GF reinforced epoxy resin (EP) composites ((RGO)10@GF/EP) have particularly significant improvement in microwave absorption properties, achieving a broad effective absorption bandwidth of 7.54 GHz and a low reflection loss of −46.02 dB. Compared with GF/EP, the bending strength and modulus of (RGO)10@GF/EP increased by 39% and 45%, respectively. The present work provides an effective solution for developing advanced composites with both broadband absorption and excellent mechanical properties.

The antibacterial property of zinc oxide/graphene oxide modified porous polyetheretherketone against S. sanguinis, F. nucleatum and P. gingivalis

About 30% failures of implant are caused by peri-implantitis. Subgingival plaque, consisting of S. sanguinis, F. nucleatum, P. gingivalis et al, is the initiating factor of peri-implantitis. Polyetheretherketone (PEEK) is widely used for the fabrication of implant abutment, healing cap and temporary abutment in dental applications. As a biologically inert material, PEEK has shown poor antibacterial properties. To promote the antibacterial activity of PEEK, we loaded ZnO/GO on sulfonated PEEK. We screened out that when mass ratio of ZnO/GO was 4:1, dip-coating time was 25 min, ZnO/GO modified SPEEK shown the best physical and chemical properties. At the meantime, the ZnO/GO-SPEEK samples possess a good biocompatibility. The ZnO/GO-SPEEK inhibits P. gingivalis obviously, and could exert an antibacterial activity to S. sanguinis in the early stage, prevents biofilm formation effectively. With the favorable in vitro performances, the modification of PEEK with ZnO/GO is promising for preventing peri-implantitis.

One-step dip-coating method for preparation of ceramic nanofiber membrane with high permeability and low cost

Ceramic nanofiber membrane (CNM) based on attapulgite (APT) without any intermediate layer neither any cracks was fabricated by a one-step dip-coating method. The effects of sintering temperature and dip-coating time on the physicochemical properties and performances of prepared CNMs were investigated. The increase of the sintering temperature up to 700 °C reduced the bending strength, porosity and chemical stability of APT-based CNMs. Meanwhile, with the dip-coating time increased, the membrane thickness increased thereafter reduced. The APT-based CNM fabricated at a sintering temperature of 600 °C and with a dip-coating time of 15 s had an average pore size of 20.4 nm, high porosity (above 60 %), good permeability of 118 L/m2 h bar and a rejection of 96.6 % polymers with a molecule weight of 600 kDa. All these properties clearly suggest the practicability of the one-step dip-coating method to prepare ceramic nanofiber membranes.

Electromagnetic Wave Absorbing Properties of Cotton Fabric with Carbon Nanotubes Coating

In order to endow cotton fabric with the electromagnetic shielding property while preserving comfort and softness, carbon nanotubes (CNTs) were coated onto NaOH pretreated fabrics via a binder-free dip-coating approach. Scanning electron microscopy (SEM) and Infrared spectroscopy were utilised to investigate the surface morphology and modification of the CNT functionalised fabrics. The effects of the number of dip-coatings, the concentration of carbon nanotubes, and the impregnation temperature on electrical conductivity, electromagnetic (EM) shielding effectiveness (SE), and wave absorbing efficiency of cotton fabrics were evaluated, respectively. The SE value of the CNT functionalised cotton fabrics increased with the dip-coating time and reached 16.5 dB after CNT dip-coating ten times, which indicates that 97.76% of the electromagnetic wave was shielded. Meanwhile, by adding layers of stacking fabrics, the SE of CNT coated fabrics was further improved to 26.4 dB. The shielding mechanism was also studied by comparing its reflection and absorption behaviour, which demonstrates that 65.7% of the electromagnetic wave was absorbed.

Core-shell type composites based on polyimide-derived carbon nanofibers and manganese dioxide for self-standing and binder-free supercapacitor electrode applications

We herein report the microstructure and electrochemical performance of core-shell type composites based on polyimide (PI)-derived carbon nanofiber (CNF) coated with manganese dioxide (MnO2) for potential applications as self-standing and binder-free supercapacitor electrode materials. For the purpose, a series of core-shell type CNF/MnO2 composites was fabricated via electrospinning of PI precursor with poly(vinyl pyrrolidone) (PVP), imidization of as-spun nanofibers, carbonization of PI/PVP nanofibers into neat CNFs, and coating of neat CNFs with MnO2 at different dipping time of 0–60 min. The Raman, X-ray diffraction and electron microscopic analyses of the core-shell type CNF/MnO2 composites revealed that MnO2 nanowhiskers were coated well on the CNFs with a turbostratic graphitic structure and their coating thickness increased with the dipping time. The electrical conductivity was measured to decrease slightly from 3.6 S/cm for the neat CNF to 1.6 S/cm for CNF/MnO2 composites with increasing the thickness of MnO2 coating layer. As a result of synergistic effects, the core-shell type CNF/MnO2 composite, fabricated at the dip-coating time of 10 min, exhibited a maximum electrochemical performance such as specific capacitance of ~456 F/g at 10 mV/s, energy density of ~17.8 Wh/kg, and power density of ~320 W/kg, in addition to good operational stability of ~95.8% capacitance retention after charge-discharge tests of 3000 cycles.

Gas sensor based on Ni foam: SnO2-decorated NiO for Toluene detection

Dense nickel oxide layer on Ni foam was prepared via a facile heating method and SnO2 nanostructures was attached to NiO through a simple dip-coating process. Construction of optimized SnO2 thin layer, which achieved by rationally adjusting of dip-coating times of Sn(OH)4, leads to a prominently enhanced sensing properties to toluene. The sensor based on NiO foam with two times of dip-coating of SnO2 exhibits the best sensing performances with 9 and 8 seconds of response and recover time and a drastic selective response (Ra/Rg = 19.2) to 10 ppm toluene at 210 °C. Furthermore, an excellent linear dependence and a 30-day measurement with little decrease on response were observed. The superior sensing behavior of toluene and relevant sensing mechanism was explained by a large surface area of NiO foam, a unique structural sensitization and a common p-n heterojunction effect.

Influence of dip-coating times towards oxygen separation performance

Several advantages possessed by carbon membrane such as can be easily processed, high gas separation performance and requires adequate amount of energy compared to the conventional separation process are the reasons it is deemed as the future media of separation. This study utilized PI blends and nanocrystalline cellulose (NCC) to prepare the tubular carbon membrane in order to investigate its fabrication. The effect of dip-coating duration (15, 30, 45, and 60 min) on physicochemical properties O2/N2 separation was determined. Carbonization was done at 800 °C with 3 °C/min rate of heating under argon gas flow (200 mL/min). Tests of pure gas permeation were conducted in order to study the transport mechanism of prepared carbon membrane at ambient temperature and 8 bar of feed pressure. Carbon membrane with O2 permeance of 29.92 ± 1.44 GPU and O2/N2 selectivity of 9.29 ± 2.54 were obtained after 45 min of dip coating.

Highly porous cobalt oxide-decorated carbon nanofibers fabricated from starch as free-standing electrodes for supercapacitors

Hybrid supercapacitor with improved energy density was prepared by electrospinning using biopolymer, and a simple dip-coating method. Through the optimization of the dip-coating time and post-heat treatment process, carbon nanofiber with highly porous structure and Co3O4 particles formed on the surface was successfully fabricated. It was found that Co3O4/C nanofibers dipped for one hour exhibited a highly porous microstructure with a specific surface area of 964 m2/g, and this was mainly composed of pores with an average diameter of 2.4 nm. These characteristics contributed to superior electrochemical properties of hybrid nanofibers, among which a 137 F/g specific capacitance was achieved with a very stable cycle life (91% retention after 5,000 cycles). The combination of porous carbon nanofiber derived by optimized calcination process of Co precursor and redox reaction from the Co3O4 provided a synergistic effect for enhanced specific capacitance of the hybrid supercapacitor.

Preparation of internally pressurized polyamide thin-film composite hollow fiber nanofiltration membrane with high ions selectivity by a facile coating method

Internally pressurized polyamide thin-film composite (TFC) hollow fiber nanofiltration (NF) membrane with high ions selectivity was prepared by a facile coating method including the dip-coating of the aqueous phase and reverse direction coating of organic phase. Surface composition and morphologies of the prepared NF membrane were characterized by ATR-FTIR, FESEM and AFM. Membrane hydrophilicity was evaluated by Water Contact Angle (WCA) measurements. The dip-coating time of the aqueous phase and reverse direction coating time of organic phase were optimized. The results indicated that the ultra-thin functional layer was successfully formed on the lumen side of hollow fiber PSF substrate membrane. Under the optimized conditions including the dip-coating time of 20 min and reverse direction coating time of 60 s, the prepared TFC hollow fiber NF membrane exhibited an excellent separation performance with the 99.5 % rejection of MgSO4 (1 g/L) and pure water flux of 43.3 L/m2h at 0.7 MPa. The prepared NF membrane showed a high selectivity with the separation factor of MgSO4/NaCl) of 7.8. NF membrane exhibited a uniform separation performance along fiber length compared with the traditional single direction coating.

Preparation of highly conductive graphene-coated glass fibers by sol-gel and dip-coating method

In order to fabricate highly-conductive glass fibers using graphene as multi-functional coatings, we reported the preparation of graphene-coated glass fibers with high electrical conductivity through sol-gel and dip-coating technique in a simple way. Graphene oxide (GO) was partially reduced to graphene hydrosol, and then glass fibers were dipped and coated with the reduced GO (rGO). After repeated sol-gel and dip-coating treatment, the glass fibers were fully covered with rGO coatings, and consequently exhibited increased hydrophobicity and high electrical conductivity. The graphene-coated fibers exhibited good electrical conductivity of 24.9 S/cm, being higher than that of other nanocarbon-coated fibers and commercial carbon fibers, which is mainly attributed to the high intrinsic electrical conductivity of rGO and full coverage of fiber surfaces. The wettability and electrical conductivity of the coated fibers strongly depended on the dip-coating times and coating thickness, which is closely associated with coverage degree and compact structure of the graphene coatings. By virtue of high conductivity and easy operation, the graphene-coated glass fibers have great potential to be used as flexible conductive wires, highly-sensitive sensors, and multi-functional fibers in many fields.

Concentration and coating time effects of N-acyl sarcosine derivatives for corrosion protection of low-carbon steel CR4 in salt water – defining the window of application

ABSTRACTPotential natural and environment-friendly substances are often used as substitutes for inhibitors to protect steel against corrosion in a sustainable way. Here, three biodegradable N-acyl sarcosine derivatives are evaluated for corrosion protection by polarisation, weight loss, electrochemical impedance, optical and scanning electron microscopy (SEM) spectroscopy including energy dispersive spectroscopy (EDS) to find the best possible application interval of concentration and dip-coating time. The substances present vary in their carbon chain length on the sarcosine-amino acid and are tested in 0.1 M NaCl as protective barrier for low-carbon steel CR4. Corrosion protection improved with increasing sarcosine concentration in the dip-coating stock solutions (25, 50, 75, and 100 mmol/L). Best efficiencies were found in polarisation for the highest studied concentrations of Oleoylsarcosine (O) with 97% followed by Myristoylsarcosine (M) with 82%. The lowest overall performance showed the shorter Lauroylsarcosine (L) with 51%. The best immersion time for dip-coating on CR4 for present compounds turned out to be 10 min. Surface analysis results with SEM and EDS revealed a significant higher C content caused by increased film-forming adsorption of sarcosines on the metal surface.

Simple and efficient fabrication of pomegranate-like Fe2O3@C on carbon cloth as an anode for lithium-ion batteries

Pomegranate-like Fe2O3@C nanoparticles on carbon cloth (CC) as an anode for lithium-ion batteries are synthesized via a combination of dip-coating and hydrothermal synthesis. The spontaneous crosslinking reaction between sodium alginate (SA) and Fe3+ first creates a chelate compound, and then the SA-Fe3+ chelate is converted to Fe2O3@C nanoparticles after a simple hydrothermal treatment. The Fe2O3@C nanoparticles exhibit pomegranate-like morphology with an average diameter of 118 nm and are composed of smaller Fe2O3@C secondary nanoparticles of 13.7 nm. Such a hierarchical nanostructure can increase the accessible surface area of the Fe2O3@C/CC electrode, leading to enhanced electrochemical efficiency for the Li+ insertion/deinsertion reaction. Furthermore, by carefully controlling dip-coating time, the Fe2O3@C nanoparticles are individually and uniformly distributed on the CC surface, which supplies expansion space for Li+ insertion and protects the electrode from structural cracks. Owing to these structural characteristics, the Fe2O3@C/CC anode material shows superior electrochemical properties for lithium-ion batteries. The first discharge capacity is as high as 1006 mAh g−1 at the current density of 0.2 A g−1, and it remains up to 1091 mAh g−1 after 100 charge/discharge cycles, implying a stable cycling ability.

Flexible, conductive, and highly pressure-sensitive graphene-polyimide foam for pressure sensor application

Three-dimensional porous graphene foams have received increasing attention in the fields of sensors, flexible conductors, and energy storage. Mechanical stability, flexibility, and electrical conductivity are prerequisites for materials used in these fields. In this paper, novel polyimide-based graphene foam was prepared by dip-coating a polyimide foam template followed by chemical reduction and thermal reduction. The prepared foam displayed excellent mechanical stability and flexibility (elastic modulus: ∼5 kPa). The synergistic effects of chemical and thermal reduction led to a foam with high electrical conductivity of ∼0.4 S m−1. By controlling the dip-coating times, the foam achieved a high pressure sensitivity of 0.36 kPa−1. Experiments show that the prepared foam can be used as effective pressure sensor to measure heartbeat, joint activity, and airflow.

A comprehensive description of the threshold flux during oil/water emulsion filtration to identify sustainable flux regimes for tannic acid (TA) dip-coated poly(vinylidene fluoride) (PVDF) membranes

In the separation of oil/water emulsions using membrane separation methods, fouling remains a problem. To improve the fouling resistance effectively, a hydrophilic tannic acid (TA) coating was constructed on the poly(vinylidene fluoride) (PVDF) membrane via dip-coating method. Both the wettability and surface free energy were dramatically enhanced after the introduction of the TA coating. TA deposition with extended dip-coating time did not result in a corresponding increase in the pure water permeate quality, suggesting that there is a trade-off between the enhanced surface hydrophilicity and diminished pore size. Furthermore, the threshold fluxes were determined using the flux-stepping method, and explored to provide guidance on membrane fouling rates for oil/water emulsion filtration. The hydrophilic TA dip-coated PVDF membrane prepared at a dip-coating time of 9 h exhibited the highest threshold flux compared to the other membranes. The experimental evidences of the threshold fluxes can be used to predict the sustainable flux regimes for the TA dip-coated membranes. Constant flux verifiable experiments for oil/water emulsion were performed at fluxes near and below the threshold fluxes. By selecting a constant flux strategy below the threshold flux, membrane over-fouling can be avoided efficiently and the operating period can be prolonged favourably. More generally, operation below the threshold flux recognizes a modest fouling level, arising from the sufficient flux, which would result in the infrequent need for cleaning and is a compromise between capital expenditure and operating costs.

Fabrication and characterization of a dense Cr2O3-Al phosphate double coating as tritium permeation barrier

A dense Cr2O3-Al phosphate double coating was fabricated by electrodeposition and dip-coating. Cr layer was firstly electrodeposited on 321 steel substrates and subsequently was thermal oxidized in air to transform into Cr2O3 layer. Then an Al phosphate film was prepared by dip-coating to seal open pores of the Cr2O3 layer. By controlling the process parameters (current density, heat-treated temperature and dip-coating times) it is possible to obtain crack-free and homogeneous double coating. The thickness of Cr2O3 layer and Al phosphate layer is 5μm and 0.6μm, respectively, when electroplating current density is 0.3A/cm2 and dip coating Al phosphate for one time. The Al phosphate layer can effectively close the open pores and decrease the porosity to 0% of Cr2O3 layer. The Cr2O3-Al phosphate double coating sample exhibits a good resistance to corrosion and improved tritium resistant performance because the Al phosphate coating successfully fills pores and defects allowing passage of gas of Cr2O3 coating. And this double coating shows good thermal cycling performance. No obvious cracks can be observed on the surface of the Cr2O3-AlPlO4 coating even after 190 cycles.

Scalable and Facile Preparation of Highly Stretchable Electrospun PEDOT:PSS@PU Fibrous Nonwovens toward Wearable Conductive Textile Applications.

Flexible and stretchable conductive textiles are highly desired for potential applications in wearable electronics. This study demonstrates a scalable and facile preparation of all-organic nonwoven that is mechanically stretchable and electrically conductive. Polyurethane (PU) fibrous nonwoven is prepared via the electrospinning technique; in the following step, the electrospun PU nonwoven is dip-coated with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This simple method enables convenient preparation of PEDOT:PSS@PU nonwovens with initial sheet resistance in the range of 35-240 Ω/sq (i.e., the electrical conductivity in the range of 30-200 S m-1) by varying the number of dip-coating times. The resistance change of the PEDOT:PSS@PU nonwoven under stretch is investigated. The PEDOT:PSS@PU nonwoven is first stretched and then released repeatedly under certain strain (denoted as prestretching strain); the resistance of PEDOT:PSS@PU nonwoven becomes constant after the irreversible change for the first 10 stretch-release cycles. Thereafter, the resistance of the nonwoven does not vary appreciably under stretch as long as the strain is within the prestretching strain. Therefore, the PEDOT:PSS@PU nonwoven can be used as a stretchable conductor within the prestretching strain. Circuits using sheet and twisted yarn of the nonwovens as electric conductors are demonstrated.

Development of Novel ECTFE Coated PP Composite Hollow-Fiber Membranes

In this work composite hollow-fibers were prepared by dip-coating of commercial polypropylene (PP) with a thin layer of ethylene–chlorotrifluoroethylene copolymer (ECTFE). The employment of N-methyl pyrrolidone (NMP) as solvent improved the polymer processability favoring dip-coating at lower temperature (135 °C). Scanning electron microscopy (SEM) analyses showed that after dip-coating the PP support maintained its microstructure, whereas a thin coated layer of ECTFE on the external surface of the PP hollow-fiber was clearly distinguishable. Membrane characterization evidenced the effects of the concentration of ECTFE in the dope-solution and the time of dip-coating on the thickness of ECTFE layer and membrane properties (i.e., contact angle and pore size). ECTFE coating decreased the surface roughness reducing, as a consequence, the hydrophobicity of the membrane. Moreover, increasing the ECTFE concentration and dip-coating time enabled the preparation of a thicker layer of ECTFE with low and narrow pore size that negatively affected the water transport. On the basis of the superior chemical resistance of ECTFE, ECTFE/PP composite hollow fibers could be considered as very promising candidates to be employed in membrane processes involving harsh conditions.

Preparation of a coated Ti anode for producing acidic electrolyzed oxidizing water

Coated Ti anodes have been prepared for producing acidic electrolyzed oxidizing water (AEOW). To improve the performance of anodes, the influence factors (sintering temperature, heat treatment time and dip-coating times) were systematically explored. The results show that the optimum sterilizing effect of AEOW is obtained in the case of sintering at 450 °C for 1 h with as many dip-coatings as possible. The sintering temperature is a critical factor. A lower temperature leads to better reaction selectivity, whereas a higher temperature results in a longer lifetime. A short heat treatment time leads to inadequate coating oxidation, a long heat treatment time prolongs the lifetime but results in high SEC. Increasing the number of dip-coatings could enhance the coating-substrate adhesion, thus extending the anode lifetime. The electrode prepared by optimization could replace the platinized Ti anode to produce AEOW. AEOW could be used as an effective disinfectant for eliminating Escherichia coli and Staphylococcus aureus. The sterilization ability is based on the combined effect of active chlorine concentration (ACC), low pH and high oxidation–reduction potential (ORP).

Redox cycling performance of inert-substrate-supported tubular single cells with nickel anode current collector

An inert-substrate-supported tubular single cell, with a configuration of porous yttria-stabilized zirconia (YSZ) supporter/Ni anode current collector/Ni–Ce0.8Sm0.2O1.9 anode/YSZ/Ce0.8Sm0.2O1.9 bi-layer electrolyte/La0.6Sr0.4Co0.2Fe0.8O3−δ cathode, has been fabricated by extrusion and dip-coating techniques. Thickness of the Ni layer is modified by controlling the number of dip-coatings from one to four. Electrochemical performance and redox cycling stability of the single cell are investigated with respect to the microstructure of the Ni layer. Increasing the thickness of the Ni layer enhances the maximum power density of the cell, while it is unfavorable for the redox cycling stability. Considering the trade-off between these two aspects, an optimum dip-coating time is determined to be two. The cell shows a reasonable maximum power density of 453 mW cm−2 at 800 °C, as well as good redox cycling stability within eight redox cycles. Additionally, 10 vol.% Ce0.8Sm0.2O1.9 ceramic particle is incorporated into the Ni layer to further improve the redox cycling stability. The cell exhibits enhanced redox cycling performance after the Ce0.8Sm0.2O1.9 incorporation. Within seven redox cycles, the cell voltage loss is less than 1% at a current density of 400 mA cm−2, and it maintains 93% of its initial performance after 11 redox cycles.

Performance improvement of inert-substrate-supported tubular single cells via microstructure modification

Inert-substrate-supported tubular single cells, with a configuration of porous yttria-stabilized zirconia (YSZ) supporter/Ni anode current collector/Ni–Ce0.8Sm0.2O1.9 anode/YSZ/Ce0.8Sm0.2O1.9 bi-layer electrolyte/La0.6Sr0.4Co0.2Fe0.8O3−δ cathode, have been fabricated. The Ni anode current collector layer is prepared by a dip-coating process, while the cathode layer is produced by drop-coating and dip-coating processes, respectively. The electrochemical performances of the single cells are examined with respect to the microstructures of these two layers. The results indicate a significant effect of the Ni layer thickness on its sheet resistance and the ohmic resistance of the single cells. The preferred dip-coating time of the Ni layer is determined to be four. At 800 °C in hydrogen fuel, the single cell with a Ni layer dip-coated for four times and a drop-coated cathode layer exhibits a maximum power density of 500 mW cm−2. The electrochemical performance of the single cell is further enhanced by modifying its cathode microstructure. Preparing the cathode layer by dip-coating for four times allows a decrease of the overall electrode polarization by 25% and an increase of the maximum power density to 555 mW cm−2.