Polyvinyl Alcohol Thin Film Research Articles

Bending Effects on Polyvinyl Alcohol Thin Film for Flexible Wearable Antenna Substrate

Polyvinyl Alcohol (PVA) has been used in various applications, including the medical health industry and electronics. It is a synthetic polymer with advantages such as being transparent, flexible, biocompatible, biodegradable, and a simpler synthesis process. These advantages make PVA a very promising material for human wearable antennae. In this research, the bending effect of an antenna using a PVA substrate is studied to analyze its durability in the wearable application. Firstly, the thin film substrate synthesis is performed using PVA 2488 with the measured average dielectric constant and tangent loss of 1.24 and 0.066, respectively, across S-Band frequency. Later, a 5G antenna is designed and fabricated using the PVA substrate. Finally, the bending effects of the fabricated antenna are measured at different bending radii. Four different antenna-bending radii are selected to represent different curvatures of human body parts. Results show that bending does not have a significant effect on the reflection coefficient of the antenna, where the frequency shifts from 2.2% up to 7.4% only for all bending conditions. Hence, in that aspect of finding, the PVA thin film is a potential candidate for flexible and wearable antenna material in various human body parts in biomedical applications.

Simultaneous measurement of temperature and humidity using a dual-parameter sensor based on SPR and no-core fiber technology

In this article, we present a surface plasmon resonance (SPR) sensor based on a no-core fiber (NCF) structure for simultaneous measurement of temperature and humidity. The sensor is simulated by depositing a silver film on the exterior of the NCF by magnetron sputtering, followed by the application of a composite thin film of polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS). This configuration induces SPR resonance phenomena at two distinct wavelengths, resulting in the splitting of the resonance peak into two distinct peaks, enabling simultaneous measurement of temperature and humidity. To achieve optimal sensor performance, the thickness of the PDMS-PVA composite film, the proportion of sensitive materials, the thickness of the silver film, and the structural parameters of the fiber were optimized. Simulation results show that the sensor exhibits a humidity sensitivity of 8.60 nm/%RH over a relative humidity (RH) range of 50%–100%. The highest temperature detection sensitivity achieved is 7.40 nm °C−1. This sensor holds great potential for applications in monitoring changes in environmental temperature and humidity.

Fabrication and Implementation of PVA Thin Film-based Relative Humidity Sensor

This paper presents the fabrication of polyvinyl alcohol (PVA)-based relative humidity sensors using copper interdigitated electrodes (IDEs). These sensors were fabricated by patterning copper IDEs onto FR4 fiberglass substrates and coating them with a thin film of PVA. By varying the number of IDE electrode pairs and the concentration of PVA, the sensors exhibited different resistance values, demonstrating an inverse relationship with the number of IDE electrodes and PVA concentration. Additionally, the thickness of the sensing layer, controlled by spin coating speed, affected the resistance of the sensors. The fabricated sensors achieved a humidity measurement range from 50% to 99% RH based on resistance changes. Furthermore, an interface circuit was designed to integrate the fabricated sensors with an ESP8266 microcontroller, achieving accurate measurements above 74% RH.

Effect of Zinc Oxide Nanostructure on the Electrical Conductivity of Polyvinyl Alcohol (PVA) Thin Films

Zinc oxide nanoparticles in the form of particles and rods were synthesized using the hydrothermal method. The scanning electron microscopy (SEM) examination was performed. The results of the SEM tests showed the nanoscale size of zinc oxide nanoparticles was (75 nm) for particles and (150 nm) for rods. An X-ray diffraction examination was carried out, and a comparison was made between the diffraction pattern of the ZnO nanoparticle and the rods. The results showed that the ZnO nanoparticle is in the hexagonal wurtzite phase of the structure of the particles and rods. Zinc oxide nanoparticles (particles and rods) produced by the hydrothermal method have been used as an additive in polyvinyl alcohol (PVA) polymer matrix to form PVA–ZnO NPs composite thin films. The optical properties of the membrane were studied using ultraviolet–visible examination, which showed a decrease in the energy gap of the composite thin film compared to the pure membrane. While the electrical properties of composite thin film, including resistivity, mobility and majority carrier charge carriers of composite thin film, were measured using the Hall effect measurement. The results showed that zinc oxide nanoparticles have a higher conductivity than nanorods.

Sensing of volatile organic compounds using one-dimensional photonic crystal Bloch surface waves and internal optical modes

Bloch surface wave (BSW) and internal optical modes (IOMs) of one-dimensional photonic crystals (1DPhCs) have been explored for sensing purposes in the photonic crystal coupled reflectance (PCCR) geometry using the Kretschmann-Raether (KR) prism-coupling configuration. 1DPhCs coated with polyvinyl alcohol (PVA) thin films of two distinct thicknesses: 18 nm (referred to as PhC18) and 24 nm (referred to as PhC24) were fabricated. The response of the PCCR to the changes occurring in the PVA coated 1DPhC structures were studied by spraying volatile organic compounds, 1-propanol and 2-propanol onto the surface of the 1DPhCs. The BSWs excited under TE polarization are found to be very sensitive to perturbations at the 1DPhC interface. 1-propanol displays larger wavelength shifts and longer recovery times of the 1DPhC modes than 2-propanol because of its lower vapor pressure and higher reactivity to PVA.

Real-time spectroscopic ellipsometry of plasmonic nanoparticle growth in polyvinyl alcohol thin films

Real-time spectroscopic ellipsometry of plasmonic nanoparticle growth in polyvinyl alcohol thin films

A review on versatile applications of polyvinyl alcohol thin films, specifically as sensor devices

AbstractPolyvinyl alcohol (PVA) thin films (PVATFs) have recently exhibited different applications in various fields, such as biomedical, optical, and energy storage. One of their outstanding applications has been known as sensor devices for various physical parameters, such as pH, pressure, gas, chemicals, strain, and humidity measurements. In this paper, after a brief review of the PVATFs biomedical, optical, and energy applications, their role as sensors is discussed in more detail. Afterward, the main preparation methods of the PVATFs sensors, for example, spin and dip coating, chemical bath deposition, and electrodeposition are surveyed. Eventually, the characterization methods of the fabricated PVATF sensors, along with their optimization techniques have been presented.Highlights Various applications of polyvinyl alcohol thin films (PVATFs) are presented. One of their main applications as sensor devices is discussed in more detail. PVATF sensors fabrication, characterization, and optimization are surveyed.

Nanopores limited domain and PVA film used to assist the SERS property of gold nanoparticle arrays

The combination of nanopores and noble metal nanoparticles has been the focus of research in recent years, and their synergistic effect enabled the substrate exhibit excellent SERS property. In this paper, the array porous silicon structures embedded with gold nanoparticles have been prepared by using the polystyrene (PS) microsphere template assisted gold annealing process and metal assisted chemical etching techniques (AuNPs@nanopore). Polyvinyl alcohol (PVA) thin film was introduced as a molecular adsorption layer to be spin coated on the surface and formed composite structure (AuNPs@nanopore @PVA) to enrich more detection molecules. Through the SERS analysis of different depths of gold nanoparticles by Rhodamine 6G (R6G) probe molecules, the optimal etching time, that is, the optimal depth that gold nanoparticles should be in, was determined. Under the etching time of 2 min, the AuNPs@nanopore @PVA structure base with pore depth of 245 nm and diameter of gold nanoparticles of 181 nm showed high sensitivity, high uniformity and the best SERS property. It can realize the low concentration detection of 10−10 mol/L R6G molecule and 10−11 mol/L methylene blue (MB) molecule, and the enhancement factor is up to 1.20 × 107. The substrate can also be used to detect the pesticide thiabendazole molecule, the detection limit of 10−8 mol/L.

Polyvinyl alcohol-based economical triboelectric nanogenerator for self-powered energy harvesting applications

Triboelectric nanogenerators (TENGs) have emerged as a promising alternative for powering small-scale electronics without relying on traditional power sources, and play an important role in the development of the internet of things (IoTs). Herein, a low-cost, flexible polyvinyl alcohol (PVA)-based TENG (PVA-TENG) is reported to harvest low-frequency mechanical vibrations and convert them into electricity. PVA thin film is prepared by a simple solution casting technique and utilized to serve as the tribopositive material, polypropylene film as tribonegative, and aluminum foil as electrodes of the device. The dielectric-dielectric model is implemented with an arch structure for the effective working of the PVA-TENG. The device showed promising electrical output by generating significant open-circuit voltage, short-circuit current, and power . Also, PVA-TENG is subjected to a stability test by operating the device continuously for 5000 cycles. The result shows that, the device is mechanically durable and electrically stable. Further, the as-fabricated PVA-TENG is demonstrated to show feasible applications, such as charging two commercial capacitors with capacitances 1.1 and 4.7 μF and powering green light-emitting diodes. The stored energy in the 4.7 μF capacitor is utilized to power a digital watch and humidity and temperature sensor without the aid of an external battery. Thus, the PVA-TENG facilitates ease of fabrication, robustness, and cost-effective strategy in the field of energy harvesting for powering lower-grid electronics by demonstrating their potential as a sustainable energy source.

Investigations on the topography and micro-mechanical properties of polyvinyl alcohol thin-film composites reinforced with hardwood biocarbon particles

In this study, we investigated the impact on surface topography and micro-mechanical properties of polyvinyl alcohol (PVA) thin films when loaded with hardwood-derived biocarbon particles (BCP). The PVA/BCP composites were prepared with the conventional film casting method, after varying BCP concentrations of 6, 8, 10, 12, and 20 wt% were added to the PVA solution. Atomic force microscopy (AFM) investigations and nanoindentation tests were performed. The average roughness of the thin films increased with the increase in BCP content. The alternation between dark and light patterns observed in the AFM images showed an irregular surface topography with alternating high peaks and deep valleys. The skewness and kurtosis parameters showed that the different dispersion degrees of the BCP within the PVA matrix influenced the composites' surface roughness. The micro-mechanical properties of the thin film composites depended on the BCP type and concentration. Films reinforced with red oak-derived BCP had higher hardness and Young's modulus compared to films reinforced with willow SV1 and yellow-poplar BCP, which was attributed to the high carbon content and low ash content of red oak BCP. We argue that these results may be extrapolated to other types of BCP-reinforced thin films and can significantly contribute to enabling more efficient methods and protocols for reinforcing polymers with hardwood biocarbon.

Comparative study of the optical and dielectric properties of PVA and silver-doped PVA

Electrolytes stand as essential components in electrochemical energy storage devices, with their physical and chemical characteristics significantly impacting device performance. Selecting the right electrolyte is pivotal for ensuring the safety and efficiency of super capacitive devices. This work explores the utilization of polyvinyl alcohol (PVA) as a host polymer in solid polymer electrolytes (SPEs) for supercapacitors and other energy storage devices. PVA based solid polymer electrolytes were synthesized by a simple casting method and investigated the effect on structural, optical and dielectric properties of polyvinyl alcohol (PVA) thin films with Ag doping. The XRD data confirms that silver-doped samples exhibit reduced crystallinity in comparison to PVA films that are pure. As a result of this decrease in crystallinity, silver-doped PVA samples exhibit improved electrical transport characteristics, making them excellent choices for Solid Polymer Electrolytes (SPE). An analysis of UV–VIS spectroscopy in silver-doped materials verifies SPR peaks at 424 nm. Exploration of the dielectric properties and frequency dependence was conducted at room temperature and silver doped samples shows higher dielectric constant values compare to pure PVA. The complex electric modulus M* of the prepared samples was also derived. The correlation between M' and M'' describes the nature of the relaxation process within the PVA/Ag NPs nanocomposite films, revealing a semicircular pattern that aligns with the Debye model.

A Universal Strategy for Modular Tunable Full‐Color Circularly Polarized Luminescent Materials with Afterglow

AbstractCircularly polarized luminescence (CPL) has shown significant potential for use in optoelectronic information and biomedical applications. Previously, the construction of CPL in thin films has often required the introduction of chiral groups into the system, which is efficient but complicated to synthesize and separate enantiomeric isomers. This manuscript proposes a simple and efficient strategy to construct dye‐doped polyvinyl alcohol (PVA) thin films with controlled orientation of the panchromatic CPL signal. This strategy can be generalized to the construction of thin‐film CPL. Besides, the metal‐free pure circularly polarized afterglow material is reported here to be adjustable. Moreover, the PVA films can be cut and stacked in a modular way to obtain different emission effects to induce mixed CPL, and three primary colors can be piled up together to induce white CPL. The PVA film has good prospects for use in optical devices, for example, anti‐counterfeiting of information and optical information encryption.

Effect of Transparency Increasing and Surface Relief of Polyvinyl Alcohol Thin Films with Graphene Oxide of Varied Concentrations: Possible Applications

Analysis of the experimentally established transmission variation (taking into account the transparency increasing) of polyvinyl alcohol thin films sensitized with graphene oxide of different concentrations was performed. The mechanical features of these solid-state compositions were studied. Transmission spectra in the visible and near-infrared ranges were registered. The microhardness of the studied materials was measured. The experimental results were confirmed by the quantum chemical modeling. A wide range of possible applications of the studied materials is proposed: display technology, light modulators, laser radiation converters, output windows of optoelectronic devices, biomedicine.

Characterizing Passively Q-switched Fiber Laser in LiDAR Application

A LiDAR system consists of a Q-switched fiber laser that emits light pulses to measure the distance from the target. We have experimentally demonstrated a passively Q-switched erbium-doped fiber laser (EDFL) by employing graphene saturable absorber (SA). The SA was prepared by dipping a polyvinyl alcohol (PVA) thin film into the graphene solution. Once the SA was fabricated, it can be placed in the cavity to perform pulses and it is operating at 1558.92 nm. The shortest pulse received is 3.9 μs and generated at the repetition rate of 115 kHz. The pulses are stable between pump powers of 59.6mW and 127.1 mW. At the maximum pump power value of127.1 mW, thelaser cavity produced pulses with a 1.4mW output power and a 1.1nJ pulse energy.

In Situ Growth of Biocompatible Biogenic Silver Nanoparticles in Poly-Vinyl Alcohol Thin Film Matrix.

Green synthesis is an eco-friendly approach of nanoparticles fabrication gaining momentum among researches. Nanoparticles are used immensely, due to its small size, physical properties, orientation, which can apparently change the performance of any other material when in proximity. Antibacterial, antioxidant, antifungal, antiviral, anti-inflammatory activities of several nanoparticles capable of wound healing make it a appropriate module for wound dressing materials. Silver nanoparticles (SNPs) are recognized as well established antimicrobial and antiseptic agents, thus considering it as a promising candidate for wound healing process and other applications. Here we report an effective and biological approach of a novel thin film preparation based on polyvinyl alcohol (PVA) with SNPs generated within matrix using leaf extract of Aloe vera as a bioreducing agent. Successful incorporation of SNPs into the polymer matrix, which was confirmed by NTA analysis, TEM, SEM. The characterization results revealed that SNPs were found in range of 10-40 nm. Evaluation of antimicrobial activity on Escherichia coli (ATCC 39403), Staphylococcus aureus (ATCC 25923), Klebsiella pneumoniae (clinical isolates), and Candida albicans (diploid fungus) using agar cup and disc diffusion method confirmed effective performance of the PVA-SNPs film. Average ZOI was observed as 3+2mm, 3+2mm, 4+1mm and 4+1mm respectively. Thin film produced is highly biocompatible to HaCat and L929 cell lines for a defined amount and hence can be used as wound dressing materials. The method used in this study is greener, simple, rapid, and cost effective for producing a biocompatible film with profoundly variable applications in food packaging and health care industries.

Synthesis and characterization PVA/plasma-functionalized MWCNTs nanocomposites films

Thin films of polyvinyl alcohol (PVA) loaded with various concentrations of (f-MWCNTs) were prepared via the regular casting method. The physicochemical characteristics of pure and PVA/f-MWCNTs films were investigated with various techniques; X-ray diffractometer (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy (UV-Vis), and thermogravimetric analysis (TGA). Moreover, the impact of loading ratios of f-MWCNTs on the dielectric constant and AC conductivity of the PVA/f-MWCNTs nanocomposite film was examined. XRD results suggest a possible improvement in the crystallinity of the PVA/f-MWCNTs composite film compared to a pristine one. Also, FTIR and XPS results confirm the formation of a hydrogen bond between PVA chains and f-MWCNTs. The optical band gaps of the PVA/f-MWCNTs composite film decrease, while the optical conductivity (σopt), dielectric constant (έ), and AC conductivity increase with increasing wt% of f-MWCNTs in the PVA matrix. Further, the thermal stability of PVA/f-MWCNTs films improved in comparison with that of PVA film.

Structural and optical studies of gamma-irradiated polyvinyl alcohol, polyethylene glycol, and lignosulfonate thin film

Thin film of polyvinyl alcohol (PVA), polyethylene glycol (PEG) and lignosulfonate (Lg) were synthesized by solution casting technique. Samples from the synthesized PVA-PEG-Lg thin film were irradiated with different γ doses ranging from 20 to 100 kGy. The resulting effect of the γ-ray irradiation on the structural and optical properties of the blend films was investigated using Fourier transform infrared spectroscopy (FTIR) and ultraviolet spectroscopy (UVs). The FTIR analysis of the blends confirmed the formation of a relatively strong hydrogen bond between the hydroxyl groups of the PVA and the blended polymers. The optical band gap, refractive index, Urbach energy, and optical dielectric parameters were characterized and interpreted based on the γ-ray dose. The optical bandgap decreased from 4.00 to 3.39 eV for a γ-ray dose of 100 kGy, associated with an increase in both Urbach energy and refractive index of the films. This could be attributed to the domination of chain crosslinking caused by γ radiation under the present conditions. Moreover, we used the Commission Internationale de E’Claire (CIE) method to evaluate the change in color between the pristine and irradiated films. The PVA-PEG-Lg film achieved significant color differences during the γ-irradiation.

Enhancing thermal conductivity and chemical protection of bacterial cellulose/silver nanowires thin-film for high flexible electronic skin

Silver nanowires (AgNWs) thin films have emerged as a promising next-generation flexible electronic device. However, the current AgNWs thin films are often plagued by high AgNWs−AgNWs contact resistance and poor long-term stability. Here, to enhance the AgNWs stability on the surface of bacterial cellulose (BC), a novel flexible high conductivity thin-film was prepared by spin-coating a layer of polyvinyl alcohol (PVA) on the BC/AgNWs (BA) film. Firstly, BC film with high uniformity to better fit the AgNWs was obtained. It is observed that inadequately protected AgNWs can be corroded when AgNWs together with PVA were attached to the BC surface (BAP film), Yet, a layer of PVA was spin-coated on the surface of BA film, the BC/AgNWs/spin-coated 0.5 % PVA (BASP) thin-film (10.1 μm) exhibits that the PVA interfacial protective layer effectively mitigated the intrinsic incompatibility of BC with AgNWs as well as external corrosion (Na2S for 3 h) and immobilization of AgNWs, thus having a low conductive sheet resistance of 0.42 Ω/sq., which was better than most of the AgNWs-containing conductive materials reported so far. In addition, the resistance of the BASP thin-film changed little after 10,000 bending cycles, and the conductivity remained stable over BC directly immersed in 0.5 % PVA/AgNWs. This “soft” conductive material can be used to manufacture a new generation of electronic skin.

Highly sensitive fiber optic humidity sensor based on polyvinyl alcohol Fabry–Perot

In this paper, a fiber optic Fabry–Perot (FP) for relative humidity (RH) sensing is presented. The proposed FP cavity is constructed by splicing a 50-mm length of no-core fiber (NCF) in a single mode fiber. Then, the end side of the NCF is coated with a polyvinyl alcohol (PVA) thin film membrane with different thicknesses (1, 2, 3, 4 µm respectively) to work as a mirror. The fringes pattern of the FP undergoes a spectral shift owing to the alteration in the PVA refractive index with the ambient RH alternative. The highest obtainable sensitivity was observed at thickness of 3 µm, which is about 0.866 nm/RH%. After that, the diameter of the NCF is tuned from 125 to 65 µm using hydrofluoric acid (HF40%) to maximize the evanescent field and thus improved sensitivity to about 0.908 nm/RH% at the diameter of 95 µm for 30% to 90% RH range. The sensor shows good stability, and easy fabricated.

Colorimetric sensor based on polymeric thin film for arsenic quantitation using colour response calibration

AbstractA simple, low‐cost and portable sensor for colorimetric determination of As(III) was developed. The sensing is carried out using a microcentrifuge tube as a mini‐reactor, where an Fe(III)‐1,10‐phenanthroline doped polyvinyl alcohol thin film is cast on the underside of the cap. Once Fe(III)‐1,10‐phenanthroline is reduced by arsine gas generated in situ from As(III), yielding the Fe(II)‐1,10‐phenanthroline complex, the red coloured product can be detected using colour analysis software. The As(III) content is then determined based upon the colour intensity of Fe(II)‐1,10‐phenanthroline on the film. Experimental conditions were optimised, and parameters affecting the complex formation and arsenic speciation were investigated. The method developed proved to be a selective colorimetric sensor for As(III). More significantly, the device could be directly used to detect As(III) in the field without any sample preparation requirements. The recovery for industrial wastewater and groundwater was found to be 97.5%‐104.0%. Hence, the thin film‐based test kit is easy to operate, portable and practical for the measurement of As(III) in the field.