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Freestanding Ag 2 S/CuS PVA films with improved dielectric properties for organic electronics
Abstract
The prime goal of this work is to synthesize free-standing polyvinyl alcohol (PVA) films doped with Ag2S, CuS, Ag2S/CuS alloy, and Ag2S/CuS nanocomposites through the sol–gel route. The dependence of Ag2S content in the PVA nanocomposite films on both the real and imaginary parts of the complex permittivity and loss tangent values was examined. An enhanced dielectric constant was achieved with minimum dielectric loss due to the insulating silica layer. By changing the Ag2S content in Ag2S/CuS PVA films, the AC conductivity is improved with pure Ag2S nanoparticles exhibiting highest values of the order of 10−6−10−9 S/cm. The Cole–Cole parameters were calculated and the semicircles observed in the plots indicate a single relaxation process. The results suggest that these composite films are potential materials for embedded capacitor applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43568.
... The high surface to volume ratio, quantum confinement effect and size tuneable physiochemical properties made quantum dot semiconductors highly recommended as dopants for polymers [4][5][6]. The polymer matrix can also fill with multiple nano systems like metal-metal, metalsemiconductor or semiconductor-semiconductor nanoparticles for achieving better physical and chemical characteristics [7][8][9][10]. Depending on the nature, composition, size and concentration of the dopants the polymer nanocomposites can be considered for tailored applications [6,[11][12][13]. ...
... Depending on the nature, composition, size and concentration of the dopants the polymer nanocomposites can be considered for tailored applications [6,[11][12][13]. The hybrid polymer films were widely promoted in the fields of integrated circuits, organic gadgets, flexible appliances, dielectric applications and micro/ nano sensors for various sensing applications [8,14,15]. A nano semiconductor -metal composites in polymers is highly encouraged for applications like memory devices, solar cells, light emitting diodes, photodiodes, organic light emitters, biolabeling, photovoltaics and many optoelectronics fields [16][17][18]. ...
... The dielectric and conductivity studies of the polymer nanocomposites were studied by applying sinusoidal voltages of different frequencies across the sample of thickness d and area A. The frequency varied dielectric studies can be explored to investigate the materials electronic homogeneity, conduction relaxation mechanisms etc. The dielectric permittivity of the material represented in the complex notation given by [1,8,57], ...
Hybrid freestanding films of polyvinyl alcohol incorporated with silver and CdZnTe quantum dots were synthesized. The effect of varying silver concentration on optical and dielectric properties were studied. Structural and morphological analysis of hybrid films were done using X-ray diffraction and transmission electron microscopy. Optical parameters like absorption coefficient, extinction coefficient, refractive index, optical bandgap, urbach energy and optical conductivity were studied for the polymer nanocomposite for 0 to 0.3 wt percentage of silver content. With increasing silver content, a decrease in bandgap energy and an increase in urbach energy was observed. Dielectric constants, loss tangent and AC conductivity values of hybrid films were found to improve, with silver addition and highest values were obtained for 0.2 wt percentage. Complex impedance plots provided semicircles and Cole-Cole parameters were calculated. The nature of impedance plot revels single relaxation process and this was effectively modelled through an equivalent RC parallel circuit.
... The CZO-PVA NCPSFs are used as dielectrics in films because they have a high dielectric constant. Interfacial or Maxwell-Wagner-Sillars polarization can better explain this phenomenon [68]. The real dielectric permittivity of the CZO-PVA NCPSFs is a measure of its ability to store electrical energy. ...
The casting aqueous solution technique was used to prepare Co: ZnO incorporated PVA nanocomposite polymer system films (CZO-PVA NCPSFs) with different wt % CZO nanopowders. Based on the Williamson-Hall equation, the values of crystallite sizes, lattice strains, dislocation densities, and stacking fault energies were found to be in the range of 27.13-72.59 nm, 4.08×10-5-1.63×10-3, 1.36×1015-1.89×1014 lines per m2 and 3.82×10-3-1.87×10-3 for the pure CZO nanopowders and 3.70 wt% CZO films, respectively. The first direct-band gap bowing parameter decreased from 5.773 eV for pure PVA to 3.117 eV for 3.70 wt% CZO. The second direct band gaps were observed at 2.741, 2.523, and 2.413 eV for the 1.85 wt% CZO, 2.78 wt% CZO, and 3.70 wt% CZO films, respectively. The first values of indirect band gaps were observed in the range of 4.708 eV for pure PVA to 3.931 eV for 3.70 wt% CZO films. The second indirect values were observed in the range of 1.651 eV for 0.18 wt% CZO to 0.599 eV for 3.70 wt% CZO films. The limiting effect of CZO-PVA NCPSFs was also affected by the doping concentration of CZO nanopowder. The values of Rb, Q, and σDC parameters were found to be in the range 7.08×107-3.89×108Ω, 9.03×10-11-6.03×10-11F, and 5.755×10-8-1.047×10-8 siemens/m for pure PVA and 3.70 wt % CZO films. Our results provide valuable insights into designing and optimizing CZO-PVA NCPSFs for optical sensing electronic applications.
... At the developing stage of power capacitors, Feng et al. [9] studied the dielectric properties of Ag/PVA nanocomposites and found an improved dielectric composite membranes that have a higher resistivity and breakdown voltage. Recently, S.Sugumaran et al. published a fruitful study regarding the hybrid PVA-InZnO thin films and its sandwich capacitor structure [10] and Aippunny et al. enhanced the dielectric properties of PVA films by Ag 2 S/CuS [11]. Due to its attractive physical properties, biocompatibility, good processability, elegant film forming, better chemical-crack resistance, optical transparency and above all, its electronic characteristics such as great insulating properties and notably high dielectric permittivity, poly (vinyl alcohol)(PVA) is a good candidate for potential applications [12][13][14][15]. ...
The capacitor structures were fabricated in the configuration of Al : CdSe/PVA : Al with CdSe/PVA as an insulating dielectric layer for high power applications. The sandwiched layer gave an excellent energy density and a better dielectric strength that was obtained from the amalgamation of CdSe and poly (vinyl alcohol). For the detailed analysis of the interaction between CdSe and PVA, transparent CdSe/PVA composites were synthesized by ultra-sonication technique with micrometer thicknesses at different wt% of CdSe. The UV absorption edge of PVA matrix corresponds to π→π* transition associated with ethylene unsaturation (C=C) was analysed and it was shifted towards higher wavelength with the CdSe incorporation. The sub-band states formation was evaluated, Urbach energy was increased up to ~835 meV, and an increase in structural defect was noticed by widening the tail state within the polymer matrix with the impurity addition. Optical parameters which include extinction coefficient (k) and index of refraction (n) have been determined. Three dielectric relaxations were pronounced as α, β and interfacial polarization and the high relative permittivity and the low values of dissipation factor indicated that the dielectric phenomenon was predominant in all membranes. Inspection of electrical conduction rate to temperatures was also investigated and the temperature coefficient of capacitance and temperature coefficient of permittivity were listed. Thermal stability could be enhanced with CdSe interaction and the variation in thermal parameters was discussed.
Recent research aims to study the structural, optical, mechanical, and dielectric characteristics of polyvinyl alcohol (PVA) filled with Cu²⁺/Zn²⁺ doped-PVA polymeric composite films. Cu²⁺/ Zn²⁺/PVA films were prepared by the solution casting method and examined by different techniques such as XRD, UV–Vis, tensile testing, and dielectric measurements. PVA’s crystallinity is affected by the interaction of the PVA’s main chain and metal ions doping. The Cu²⁺-ions codoped Zn/PVA composite films reveal the absorbance spectrums in the visible region due to the surface plasmonic resonance (SPR) phenomenon for Cu-particles. It is found that the mechanical characteristics were improved, where the strength, Young’s modulus, and ductility were increased through the increase of Cu²⁺-ions content in Zn/PVA composite films. The dielectric measurement of the as-prepared polymeric composite films has investigated and demonstrated a highly attractive dielectric constant for the polymeric dielectric media. The obtained dielectric behaviors, alternating-current conductivity, and dielectric modulus depended on the Cu²⁺-ions content. The power output is reduced by increasing Cu²⁺-ions content, and therefore, the optical limiting of polymeric films becomes better. Finally, Cu²⁺-ions doped Zn/PVA composite films showed unique properties to be used as flexible electronic and optoelectronic devices, especially in dielectric media, CUT-OFF laser filters for biomedical laser applications.
Graphical abstract
The combination of high fire retardancy, high strength, and great toughness as well as good healability is essential for successful real-world applications of polymeric materials in the fields of packaging, electronics & electrics, and optical devices. To date, there have been few successes in achieving such performance portfolios in polymers due to their different and even mutually exclusive governing mechanisms. Inspired by the nanoconfinement effect that governs the unique mechanical properties of spider silk, we, herein, rationally design a multifunctional small molecule, HCPA, that can serve as a fire retardant and hydrogen-bond crosslinker for poly(vinyl alcohol) (PVA). Benefiting from the dual-phase fire-retardancy effect and the dynamic cross-linking effect, the addition of 5.0 wt% of HCPA enables PVA to achieve a desired self-extinguishment in combination with a high tensile strength of 133 MPa and a toughness of 112 MJ/m³. In addition, the as-prepared polymer material exhibits a high healing efficiency of over 90% (based on strength) if triggered by water. This proof-of-concept opens numerous opportunities for the creation of self-extinguishing, strong, tough, and self-healing polymers for many high-end applications in the above-mentioned industries.
Polymer hybrid films were prepared by solution casting technique, using polyvinyl alcohol–polyethylene glycol (PVA–PEG) blend host matrix as the organic component and Ag2S (in-situ formed) as the inorganic component. Differential scanning calorimetry (DSC) studies revealed the increased flexibility of polymer hybrid films, when compared to pure PVA–PEG blend film. Thermal stability of the hybrid film PPS3 (with AgNO3:Na2S ratio equal to 3.0 ml: 1.5 ml) which has uniformly distributed Ag2S nanostructures is more, when compared to other hybrid films, as revealed by thermogravimetric analysis (TGA). Polymer hybrid film PPS1 (with AgNO3:Na2S ratio equal to 1.0 ml: 0.5 ml) which has uniformly distributed Ag2S microstructures shows increased values of tensile strength and percentage elongation at break. The presence of Ag2S nanoparticles in PPS3 film has increased the overall toughness of the corresponding hybrid film. The highest bulk conductivity equal to 1.43 × 10–5 Sm⁻¹ is observed for PPS4 film (with 4.0 ml: 2 ml ratio of precursors), which has a comparatively lower degree of crystallinity and porous structure. Impedance spectroscopy studies reveal that Ag2S filler, in its micro and nano forms, can substantially improve the AC conductivity and dielectric properties of PVA–PEG polymer blend (loaded with Ag2S).
A novel flexible free-standing films of polyvinyl alcohol (PVA)/silica polymer network dispersed cholesteric liquid crystals (CLC) have been prepared by the sol-gel process. In the hydrolysis of silicon alkoxides tetraethoxysilane (TEOS) processes, the silica having -OH with the -OH groups on PVA formed polymer networks with Si-O-C bonds by dehydration. The cholesteric liquid crystals were incorporated into the networks. The free-standing films were obtained by the spin-coating method. In order to improve the compatibility and microstructure of the cholesteric liquid crystals with PVA/silica polymer networks, the amphiphilic compound of hexadecyl trimethyl ammonium bromide (HDTMA) was introduced into the forming film solutions. Effects of the different ratios of raw materials on the structure of films were investigated. The microscopic morphology of free-standing films and the uniform dispersion of CLCs in the films have been characterized by polarizing optical microscopy (POM), the field emission scanning electron microscope (FESEM), Fourier transform infrared (FT-IR) spectrometer and atomic force microscope (AFM). The free-standing films exhibiting excellent CLC droplets dispersion, mechanical stability, and good flexibility could be useful for flexible displays, switchable optical elements and smart windows.
Multifunctional transparent composite films with high dielectric permittivity (high-k), breakdown strength, and mechanical properties are urgently required by cutting-edge fields. Herein, novel multifunctional films were facilely prepared through building unique cross-linked structure based on epoxy resin (EP) and polyacrylonitrile (PAN)-lithium trifluoromethane sulfonate (LiTf) complex. Compared with high-k materials reported previously, EP/(PAN-LiTf) films simultaneously show very high transparency, good flexibility, high tensile, and breakdown strengths. For 0.22EP/(PAN-LiTf) film with 22 wt % EP, its average transmittance and elongation at break are as high as 91% (600-800 nm) and 12.7%, respectively; moreover, its dielectric permittivity, AC breakdown strength and the maximum energy density are severally about 4.9, 1.8, and 15.2 times of those of EP resin, completely overcoming the sticky problems in conductor/polymer composites. The origin behind these attractive properties is intensively discussed, and believed to be attributed to the unique structure of EP/(PAN-LiTf) films.
In this letter, we report flexible, non corrosive, and light weight nickel nanoparticle@multi-walled carbon nanotube-polystyrene (Ni@MWCNT/PS) composite films as microwave absorbing material in the frequency range of S band (2-4 GHz). Dielectric permittivity and magnetic permeability of composites having 0.5 and 1.5 wt. % filler amount were measured using the cavity perturbation technique. Reflection loss maxima of -33 dB (at 2.7 GHz) and -24 dB (at 2.7 GHz) were achieved for 0.5 and 1.5 wt. % Ni@MWCNT/PS composite films of 6 and 4 mm thickness, respectively, suggesting that low concentrations of filler provide significant electromagnetic interference shielding.
Energy storage capacitors have been the focus of increasing attention due to their advantages such as handiness, high efficiency and environment friendliness. To obtain the dielectric capacitor composites, poly(vinylidene fluoride) (PVDF) and conductive polyaniline (PANI) were selected as the polymer matrix and the filler respectively. The influences of volumetric fraction of PANI (fPANI), preparation processing and frequency on dielectric properties were studied. The results showed when the fPANI was up to 0.05 (higher than the percolation threshold fc = 0.042), the dielectric permittivity of the hybrid film was as high as 385 (at 103 Hz), the breakdown strength was 60 MV m−1, and the energy storage density was 6.1 J cm−3, which was three times higher than that of neat PVDF. Moreover, the dielectric permittivity was frequency-independent even for the hybrid films with the fPANI approaching the fc. SEM and XRD revealed that the PANI can be dispersed uniformly in the PVDF matrix, and that the PVDF existed mainly as typical β-crystal PVDF for our preparation method. Percolative theory and microcapacitor modeling were employed to explain these results. This route was demonstrated to be effective to prepare the high energy density capacitor material used in the wide frequency range.
In this article, we present the exploration of a facile synthetic tactic incorporating delay-photo-oxidation to recover the loss in emission frequently encountered after encapsulating quantum dots (QDs) inside a silica shell. This facile synthesis procedure reproducibly increases emissive intensity of QDs (core)-SiO(2) (shell) (60 nm) nanomaterials by >5 fold (QY from 3% to >15%). The resulting QDs (core)-SiO(2) proved to be a single quantum dot in single SiO(2), homogeneous and highly monodispered; their emissions have been successfully fine-tuned from visible to the near infrared region. We then demonstrate their power in biological imaging by labeling human mesenchymal stem cells under two-photon confocal microscopy. The results of low cytotoxicity, efficient labeling, and specific location nearby the nucleus characters of these nanoparticles should spark an intensive relevant research within a living system.
TiO2 nanotubes functionalized with copper sulfide quantum dots were successfully prepared by a stepwise crystallization of CuS nanoparticles onto the nanotubes, using cysteine linkers. The products were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV−vis spectroscopy, and fluorescent spectroscopy. Photocatalytic behavior of CuS/TiO2 nanotubes was evaluated for photodecomposition of malachite green and phenol. The effect of CuS QDs was investigated by photobleaching of malachite green in a Ray-sorb reactor (optical filtration at wavelength <600 nm). The results suggest that CuS QDs can enhance photocatalytic activity and improve photosensitivity of the TiO2 nanotubes using visible light.
Nanometre-sized CdS semiconductor particles were synthesized in the presence of sodium citrate, and subsequently surrounded by a homogeneous silica shell. The coating procedure makes use of 3-(mercaptopropyl) trimethoxy silane (MPS) as a surface primer to deposit a thin silica shell in water. The dispersion is then transferred into ethanol, where thicker shells can be grown. The citrate-stabilized particles are slowly degraded through photochemical oxidation in the presence of dissolved oxygen. This destabilizing process is suppressed when a homogeneous, microporous silica shell is built up around the particles, through a limited access of O2 molecules to the CdS surface.
The use of nanometre thick silica shells as a means to stabilize metal clusters and semiconductor particles is discussed, and its potential advantages over conventional organic capping agents are presented. Shell deposition depends on control of the double layer potential, and requires priming of the core particle surface. Chemical reactions are possible within the core, via diffusion of reactants through the shell layer. Quantum dots can be stabilized against photochemical degradation through silica deposition, whilst retaining strong fluorescence quantum yields and their size dependent optical properties. Ordered 3D and 2D arrays of a macroscopic size with uniform particle spacing can be created. Thin colloid films can also be created with well-defined interparticle spacing, allowing controlled coupling of exciton and surface plasmon modes to be investigated. A number of future core–shell nanocomposite structures are postulated, including quantum bubbles and single electron capacitors based on Au@SiO2.
New light-weight, flexible dielectric composite materials were fabricated by incorporation of several new carbon nanostructures into a dielectric host matrix. Both permittivity and loss tangent values of the resulting composites were widely altered by varying the type and content of the conductive filler. The dielectric constant was tuned from moderate to very high values, while the corresponding loss tangent changed from ultra-low through extremely high. The data exemplifies that nano-scale changes in the structure of the conductive filler results in dramatic changes in the dielectric properties of composites. A microcapacitor model most explains the behavior of the dielectric composites.
A novel PVA/CuI nanocomposite polymer electrolyte layer synthesized via the reduction of CuCl2 by NaI in an aqueous PVA solution. The as-prepared films were characterized by X-ray diffraction, scanning electron microscope, as well as impedance spectroscopy. The obtained results indicated the formation of hexagonal CuI nano particles of ≈55nm sizes embedded in the PVA matrix. In addition, the study of dielectric parameters and conductivity of PVA/CuI nanocomposite in wide range of temperature and frequency are given and discussed. The frequency dependence of ac-conductivity suggests power law with an exponent 0.026
A modified inverse microemulsion technique was used to synthesize coated Ag2S/CdS nanocomposites of 10 nm in diameter. Their nonlinear absorption was observed with picosecond and nanosecond laser radiation of 532-nm wavelength. The nonlinear absorption in the Ag2S/CdS nanocomposites was enhanced, in comparison with the CdS nanoparticles, due to free-carrier absorption. In addition, the relaxation times of photoexcited free carriers in the Ag2S/CdS nanocomposites were also determined to be a few nanoseconds.
A three-phase percolative composite with a ferroelectric phase (BaTiO3) and metallic inclusions (Ni) embedded into polyvinylidene fluoride matrix was prepared by using a simple blending and hot-molding technique. Effective medium approximations and percolation theory were employed in order to design and describe the dielectric behavior of such three-phase composites. Our experimental results showed that the static dielectric constant of such a three-phase composite can reach above 800 when the Ni concentration is close to its percolation threshold. Such composites have a potential to become capacitors and can be easily fabricated into various shapes due to its flexibility. © 2002 American Institute of Physics.