Study of Electrical and Thermal Properties of PVA-Nanosilica as A Candidate for Supercapacitor Separators

Separator in the supercapacitor that separates the cathode from the anode has an important role in a supercapacitor circuit. Polyvinyl Alcohol (PVA) is a substitute for polyolefin which is commonly used as a supercapacitor separator and PVA has more environmentally friendly properties. The addition of silica dioxide nanocomposites is useful for adding thermal stability and electrical insulators. The method used to make the separator is quite simple, namely by casting a PVA gel membrane with nanosilica on a glass plate and drying it at low temperature. PVA membrane with nanosilica variations different precursors are from sand by coprecipitation method and from TEOS. The properties of the two samples were characterized by scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), and LCR meter. Nanosilica derived from sand and from TEOS have no much different characteristic.

Transient Response of the Acid-base Diode for Polarity Change

An application of the so-called acid-base diode would be the sensitive detection of nonhydrogen cations in an acidic medium based on salt-effects. For diode purposes different connecting elements between the acidic and aqueous reservoirs of the diode were developed, namely a polyvinyl alcohol (PVA) hydrogel cylinder, and a polyvinyl butyral (PVB) membrane. During the measurement of the voltage – current characteristic (VCC) of the diode, it was found, that in the case of PVA gel cylinder an overshoot (a local maximum followed by a local minimum) appeared in the time vs. current curve, while the diode was switched between modes (open or closed), that is the direction of the applied voltage was reversed. The overshoot did not appear in PVB membrane.The existence of overshoots was studied by numerical simulations. The time response of the diode with different hypothetic connecting elements was investigated, when the diode was switched between modes via changing the polarity of applied voltage. We found that larger diffusion coefficients of hydrogen and hydroxide ions explain the appearance of overshoots. By examining the concentration and potential profiles a qualitative explanation of this phenomenon was given.

Linear Dynamic Viscoelasticity of Dual Cross-Link Poly(Vinyl Alcohol) Hydrogel with Determined Borate Ion Concentration

We investigated the linear dynamic viscoelasticity of dual cross-link (DC) poly(vinyl alcohol) (PVA) (DC-PVA) hydrogels with permanent and transient cross-links. The concentrations of incorporated borate ions to form transient cross-links in the DC-PVA hydrogels (CBIN) were determined by the azomethine-H method. The dynamic viscoelasticity of the DC-PVA hydrogel cannot be described by a simple sum of the dynamic viscoelasticity of the PVA gel with the same permanent cross-link concentration and the PVA aqueous solution with the same borate ion concentration (CB = CBIN) as in the DC-PVA gel. The DC-PVA hydrogel exhibited a considerably higher relaxation strength, indicating that the introduction of permanent cross-links into temporary networks increases the number of viscoelastic chains with finite relaxation times. In contrast, the relaxation frequency (ωc) (given by the frequency at the maximum of loss modulus) for the DC-PVA hydrogel was slightly lower but comparable to that for a dilute PVA solution with the same CB. This signifies that the relaxation dynamics of the DC-PVA hydrogels is essentially governed by the lifetime of an interchain transient cross-link (di-diol complex of boron). The effect of permanent cross-linking on the relaxation dynamics was observed in the finite broadening of the relaxation-time distribution in the long time region.

Preparation and bacteriostatic research of porous polyvinyl alcohol / biochar / nanosilver polymer gel for drinking water treatment

Microbial contamination in drinking water has become an important threat to human health. There is thus an urgent need to develop antibacterial materials to treat drinking water. Here, porous silver-loaded biochar (C–Ag) was prepared using corn straw as the substrate and silver as the antibacterial agent. C–Ag was then uniformly distributed in polyvinyl alcohol gel beads of eluted calcium carbonate to prepare p-PVA/C–Ag antibacterial composite. The polymer composites were tested by FT-IR, XRD, SEM and TG-DSC. The results showed that C–Ag was more evenly distributed in the PVA gel spheres. Antibacterial experiments showed that p-PVA/C–Ag greatly inhibited Escherichia coli. Practical application tests revealed that p-PVA/C–Ag showed high and sustained bactericidal inhibition and reusability. Generally, p-PVA/C–Ag composite shows high potential to be applied to drinking water treatment.

Co-electrospun-electrosprayed PVA/folic acid nanofibers for transdermal drug delivery: Preparation, characterization, and in vitro cytocompatibility

In this study, hydrophilic based bioactive nanofibers were produced via an electrospinning and electrospraying simultaneous process. Poly(vinyl alcohol) (PVA), poly(vinyl alcohol)-gelatin (PVA-Gel), and poly(vinyl alcohol)-alginate (PVA-Alg) polymers were used as the matrix material and folic acid (FA) particles were dispersed simultaneously on the surface of the nanofibers. The morphology of the nanofibers (NFs) was uniform and confirmed by scanning electron microscopy. Thermal behavior, chemical structure of the composite nanofibers were investigated by thermogravimetric analysis, and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy which showed that no chemical bonding between vitamin and polymers. A fast release of FA-loaded electrospun fibers was carried out by UV-Vis in vitro study within the 8 hour-period in artificial sweat solutions (pH 5.44). The obtained PVA/FA, PVA-Gel/FA, and PVA-Alg/FA fibers released 49.6%, 69.55%, and 50.88% of the sprayed FA in 8 h, indicating the influence of polymer matrix and polymer-drug interactions, on its release from the polymer matrix. Moreover, biocompatibility of all developed novel NFs was assessed by two different cytotoxicity tests, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and neutral red uptake (NRU) assay in L929 (mouse fibroblasts) cell lines. In all cases, it is concluded that these new electrospun fibers had fast-release of the vitamin and the hybrid process is suitable for transdermal patch applications, especially for skin-care products. The results of cytocompatibility assays on L929 reveal that all prepared NFs have no or slight cell toxicity. PVA and PVA-Gel with/without FA nanofibers seems more biocompatible than PVA-Alg nanofibers.

Fumed SiO2-H2SO4-PVA Gel Electrolyte CO Electrochemical Gas Sensor

The conventional CO electrochemical gas sensor uses aqueous H2SO4 solution as electrolyte, with inevitable problems, such as the drying and leakage of electrolyte. Thus, research on new alternative electrolytes is an attractive field in electrochemical gas sensors. In this paper, the application of a new fumed SiO2 gel electrolyte was studied in electrochemical gas sensors. The effects of fumed SiO2 and H2SO4 contents on the performance of the CO gas sensor were investigated. The results showed that the optimized composition of the SiO2 gel electrolyte was 4.8% SiO2, 38% H2SO4, and 0.005% polyvinyl alcohol (PVA). Compared with aqueous H2SO4, the gel electrolyte had better water retention ability. The signal current of the sensor was proportional to the CO concentration. The sensitivity to CO was 78.6 nA/ppm, and the response and recovery times were 31 and 38 s, respectively. The detection limit was 2 ppm. The linear range was from 2 to 500 ppm. The gel electrolyte CO sensor possesses equivalent performance to that with aqueous electrolyte.

Seawater Desalination by Interfacial Solar Vapor Generation Method Using Plasmonic Heating Nanocomposites

With the ever-growing demand in fresh water supply, great efforts have been devoted to developing sustainable systems which could generate fresh water continuously. Solar vapor generation is one of the promising strategies which comprise an unlimited energy source and efficient solar-to-heat generators for overcoming fresh water scarcity. However, current solar vapor generation systems suffer either from inefficient utilization of solar energy or an expensive fabrication process. In this paper, we introduced a nano-plasmonic approach, i.e., a floatable nanocompoiste where copper sulfide nanorods (Cu2-xS NRs) are embedded in a polyvinyl alcohol (PVA) matrix, for solar-to-vapor generation. A high solar vapor generation efficiency of ~87% and water evaporation rate of 1.270 kg m−2 h−1 were achieved under simulated solar irradiation of 1 sun. With the illumination of natural daylight, seawater was purified using Cu2-xS NRs-PVA gel, with high purity, as distilled drinking water. The plasmonic nanocomposites demonstrated here are easy to fabricate and highly efficient for solar vapor generation, illustrating a potential solution for future seawater desalination.

CNTs Supercapacitor Based on the PVDF/PVA Gel Electrolytes

Background: In this paper, the supercapacitor based on the carbon nanotubes (CNTs) electrodes has been fabricated. Objective: The Polyvinylidene Fluoride (PVDF) and Polyvinyl Alcohol (PVA) were used as a gel electrolyte. Methods: The electrodes and electrolytes thin films were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The specific Capacitance (Cs) of the CNTs-based supercapacitor has been measured using the cyclic voltammetry and galvanostatic methods. For the scan rate, 20 mV s-1 the Cs of the CNTs-based supercapacitor was 173 F g-1. Results: Using the electrochemical impedance spectroscopy the Nyquist curve has been plotted. The reactance capacitance and the equivalent series resistance of the CNTs-based supercapacitor with PVDF/PVA gel electrolytes were 90 Ω and 25 Ω respectively. Conclusion: Also, few patents for the CNTs-based supercapacitor have been reviewed and cited. The CNTs-based supercapacitor proposed a new structure solid-state and flexible supercapacitor with high performance.