PVA Thin Films Research Articles

Simple and non-toxic fabrication of poly(vinyl alcohol)-patterned polymer surface for the formation of cell patterns

Abstract In this study, a facile and non-toxic method for the formation of cell-adhesive poly(vinyl alcohol) (PVA) patterns on the surface of a non-biological polystyrene substrate (NPS) is developed to control cellular micro-organization. PVA thin films spin-coated onto the NPS are selectively irradiated with 150 keV H+ ions through a pattern mask and developed with deionized water to form negative-type PVA patterns. Well-defined stripe patterns of PVA with a width of 100 μm are created on the NPS at a higher fluence than 5 × 1015 ions/cm2, and their surface chemical compositions are changed by ion irradiation without any significant morphological change. Based on the results of the protein adsorption test and in vitro cell culture, cancer cells are preferentially adhered and proliferated onto the more hydrophilic PVA regions of the PVA-patterned NPS, resulting in well-defined cell patterns.

Ultrahigh-Resolution MEMS Humidity Sensing Elements Based on Film Bulk Acoustic Wave Resonators

A high-resolution humidity sensor based on MEMS FBAR with spin-coated PVA thin film is reported. The sensors exhibit very high sensitivity to water vapor and are able to detect down to 0.08 % change in relative humidity by monitoring the shift in series resonant frequency of the FBARs. The integration of these devices with CMOS oscillating circuits and RF front-end chips will create great potential of FBAR based mass sensors in a wide variety of applications in chemical and biological sensing.

Tribological properties of PBO fabric composites modified by poly (vinyl alcohol)

ABSTRACTFriction and wear behaviors of poly (vinyl alcohol) (PVA) modified PBO fabric composites were evaluated in a pin‐on‐disc friction and wear tester, and the relationship between the properties and the structure change resulting from PVA modification were intensively investigated using thermogravimetric analysis (TG) and scanning electronic microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The results indicated that the PVA thin film formed on the fabric surface by chemical crosslinking reaction could improve the antiwear property of the PBO fabric composites efficiently. In argon‐300°C condition, the antiwear property of the PBO fabric composites was improved by 35%, which was due to the improvement of the bonding strength between the fabric and resin and the dispersion of the shear stress induced by the shear creep and plastic deformation of the PVA film in friction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1313‐1320, 2013

Effect of electron beam irradiation on the structural, thermal and optical properties of poly(vinyl alcohol) thin film

Poly(vinyl alcohol) (PVA) polymer was prepared using the casting technique. The obtained PVA thin films have been irradiated with electron beam doses ranging from 20 to 300 kGy. The resultant effect of electron beam irradiation on the structural properties of PVA has been investigated using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), while the thermal properties have been investigated using thermo-gravimetric analysis and differential thermal analysis (DTA). The onset temperature of decomposition T 0 and activation energy of thermal decomposition E a were calculated, results indicate that the PVA thin film decomposes in one main weight loss stage. Also, the electron beam irradiation in dose range 95–210 kGy led to a more compact structure of the PVA polymer, which resulted in an improvement in its thermal stability with an increase in the activation energy of thermal decomposition. The variation of transition temperatures with electron beam dose has been determined using DTA. The PVA thermograms were characterized by the appearance of an endothermic peak due to melting. In addition, the transmission of the PVA samples and any color changes were studied. The color intensity Δ E was greatly increased with increasing electron beam dose, and was accompanied by a significant increase in the blue color component.

Hollow bimetallic nanoparticles generated in situ inside a polymer thin film: fabrication and catalytic application of silver–palladium–poly(vinyl alcohol)

Hollow bimetallic nanoparticles of silver–palladium (Ag–Pd) are generated in situ inside poly(vinyl alcohol) (PVA) thin films by a two-stage process. In the first stage, Ag–PVA is fabricated by mild thermal treatment of a spin-coated thin film, with the polymer functioning as the reducing agent for the embedded metal precursor ions as well as the stabilizer for the generated nanoparticles. In the second stage, an aqueous solution of potassium palladium chloride (K2PdCl4) is spread on this film under ambient conditions, whereupon Pd gets deposited on the Ag nanoparticles through a Galvanic displacement reaction and alloys with it. A crucial requirement of relatively large Ag nanoparticles that can act as the sacrificial template in the second stage is met by the addition of catalytic amounts of cupric ions in the first stage. A gradual variation of the concentration of K2PdCl4 solution used in the in situ process allowed a systematic demonstration of the evolution of the bimetallic nanoparticles with the eventual formation of hollow particles with Ag–Pd alloy walls. The high catalytic efficiency of the Ag–Pd hollow nanoparticle-embedded PVA thin film is demonstrated by its application in the Suzuki–Miyaura reaction.

Synthesis, structural, optical and electrical properties of metal nanoparticle–rare earth ion dispersed in polymer film

Cu-nanoparticles have been prepared by ablating a copper target submerged in benzene with laser pulses of Nd:YAG (wavelength: 355, 532 nm and 1,064 nm). Colloidal nanoparticles have been characterized by UV–Vis spectroscopy and transmission electron microscopy. The obtained radius for the nanoparticles prepared using 1,064 nm irradiation lies in the range 15–30 nm, with absorption peak at 572 nm. Luminescence properties of Tb3+ ions in the presence and absence of Cu-nanoparticles have been investigated using 355 nm excitation. An enhancement in luminescence of Tb3+ by local field effect causing increase in lifetime of 5D4 level of Tb3+ ion has been observed. Frequency and temperature-dependent conductivity of Tb3+ doped PVA thin films with and without Cu-nanoparticles have been measured in the frequency range 20 Hz–1 MHz and in the temperature range 318–338 K (well below its melting temperature). Real part of the conductivity spectra has been explained in terms of power law. The electrical properties of the thin films show a decrease in dc conductivity on incorporation of the Cu-nanoparticles.

Investigations on electrical properties of poly(vinyl alcohol) doped with 1-methyl-3-n-decyl-imidazolium bromide ionic liquid

Thin films of poly(vinyl alcohol) (PVA) that are 100–500 μm thick were prepared by solution casting method. Various ratios of 1-methyl-3-n-decyl-imidazolium bromide ionic liquid [MDIM](+)Br(−), were used as dopants (plasticizers) to control the conductivity of the PVA thin films. Fourier transform infrared spectroscopy (FTIR) was used to indicate the detailed interaction of PVA with proton of the dopant in the blends. Ac impedance spectroscopy was used to investigate the impedance of the films within a frequency range of 10–106 Hz as a function of temperature between 298 and 425 K. Each film with a precise doping concentration was sandwiched between two stainless–steel electrodes. The results showed that the electrical conductivity can be engineered by controlling the [MDIM](+)Br(−) doping concentration. Therefore, those films have potential to be used in flexible and cheap organic device applications.

Microfluidic etching for fabrication of flexible and all-solid-state micro supercapacitor based on MnO2 nanoparticles

Micro-supercapacitors are a promising candidate whose reliability and performances are struggling to meet the energy demands dictated by the incoming generation of miniaturized electronic devices. In this paper, we describe a facile and low-cost method for fabricating flexible and all-solid-state micro supercapacitors by microfluidic etching. The micro-supercapacitor configuration is composed of sub-10-nm-scale MnO(2) nanoparticle interdigital microelectrode fingers prepared by microfluidic etching with H(3)PO(4)-PVA thin films as both the solid-state electrolyte and the flexible substrate. The entire device shows outstanding electrochemical performances with high specific capacitance and stable cycle life, and the performance can be mostly preserved even conditions of under repeated bending. The technique we describe here is a universal method for fabricating a micro-supercapacitor, since the microfluidic etching can be extended to most active materials which can be used for energy- and power-devices, and there are many other choices for the solid electrolyte. Thus, these micro-supercapacitors provide a promising power source in microelectromechanical systems (MEMS), wearable electronics and other general requirements.

Dielectric function of polymer nanocomposites in small filling factor approximation

The dielectric function of polymer nanocomposites is examined in a small filling factor approximation (SFFA). The linear concentration dependence on SFFA is experimentally confirmed by refractometric investigations of PVA thin films doped with titania and diamond nano-sized particles.

NONLINEAR REFRACTION AND PHOTOINDUCED BIREFRINGENCE IN THE METHYL-RED-DOPED POLYMER THIN FILM

Single beam Z-scan measurement has shown that the methyl-red-doped PVA thin film possesses a large nonlinear refractive index: n2 ( cm 2/ W ) = -2.29 × 10-4 cm 2/ W and n2 ( cm 2/ W ) = -8.75 × 10-5 cm 2/ W for the CW 532 nm linear polarization light and circular polarization light, respectively. The mechanism for the process of nonlinear refraction is discussed in terms of the photoisomerization of MR molecules. Moreover, photoinduced birefringence with values on the order of 10-4 has been observed when investigating the photoinduced birefringence of the thin film with a CW 532 nm laser as the pump light and a CW 650 nm laser as the probe light.

Fluorescence properties of pyrene derivative aggregates formed in polymer matrix depending on concentration

We investigated the fluorescence properties of dye aggregates formed in a poly(vinylalcohol) (PVA) matrix by phase separation. Trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide (PyAm) was used as a fluorescent dye molecule. The size of PyAm aggregates in the PVA thin films were increased with increasing dye concentration, which was confirmed by atomic force microscope (AFM) measurements. The fluorescence spectra of PyAm in the PVA film at a lower concentration of 0.001 mol% only showed the monomer emission. The fluorescence peak shifted to the red with increasing dye concentration, which was assigned to a dimer or excimer-like emission. Changes in the fluorescence spectra relate to the formation of aggregates in the films. The fluorescence anisotropy decay time constant increases with increasing PyAm concentration up to the order of 100 ps. It is suggested that the exciton efficiently diffuses within the aggregates, and then was trapped at the dimer sites. We also demonstrated the application for gas sensing of nitroaromatics: 2,4-dinitrotoulene (DNT) based on the fluorescence quenching by the photoinduced electron transfer. The quenching efficiency of PyAm fluorescence reached about 43% under concentration of 2.0 mol%. The fluorescence intensity efficiently quenched at the dimer or excimer-like band. These results indicated that the efficient fluorescence quenching increases the reaction probability between PyAm and DNT by the exciton diffusion in the aggregates, called "amplified quenching". The nano-sized aggregates of PyAm formed in the PVA films are responsible for high sensitivity as an artificial fluorescent chemosensor for vapors of the nitroaromatics.

Poly (vinyl alcohol) thin film filled with CdSe–ZnS quantum dots: Fabrication, characterization and optical properties

A transparent poly (vinyl alcohol) (PVA) nanocomposite thin film (30–50 nm) reinforced with core/shell cadmium selenide (CdSe)/zinc sulfide (ZnS) quantum dots (QDs) was fabricated by a drop-casting method. A narrow peak at ∼556 nm observed in the UV–vis spectrum indicates the uniformly dispersed QDs in the PVA matrix. FT-IR analysis indicates the interaction between the QDs and the polymer matrix. Both PVA and PVA-QDs nanocomposite thin films show polarized light dependent absorption properties with several different absorption peaks. As compared to the only fluorescent emission peak at 574 nm of QDs, the pure PVA and PVA-DDs nanocomposites show an excitation wavelength dependent fluorescent emission property.

Adhesion improvement of poly (vinyl alcohol) coating on silicon substrate

The adhesion of the biocompatible hydrophilic polymer, poly (vinyl alcohol) to a model substrate, silicon, was investigated. Contact angle measurements were used to reveal the effect of various substrate cleaning procedures including sonication and UV–ozone treatment prior to casting a 35 μm coating. Raman microspectrometry and X-ray reflectometry were used to characterise the composition and the thickness of PVA thin films. The use of mechanical abrasion of the substrate followed by a 131 nm primer layer of PVA in combination with vacuum treatment at temperatures higher than the glass transition temperature ( T g = 80 °C) provided the best resistance to delamination as demonstrated by visual observation during prolonged immersion of the coatings in water.

Nonlinear refraction and photoinduced birefringence in chlorophosphonazo I doped polymer thin films

The nonlinear refraction and photoinduced birefringence of chlorophosphonazo I (CPA I ) doped PVA thin films were investigated. The single-beam Z-scan measurement showed that CPA I doped PVA thin film possessed a large value of nonlinear refractive index ( n 2=1.82×10 −12 cm 2/W) under a pulse 532 nm excitation, and the mechanism accounting for the process of nonlinear refraction was discussed in term of resonant electronic effect. Moreover, fast and stable molecular reorientation was observed when investigating the photoinduced birefringence of CPA I doped PVA thin film with a CW 532 nm laser as pump light and a CW 650 nm laser as probe light.

High Performance Pentacene Thin Film Transistors with a PVA Gate Dielectric

Pentacene thin film transistors were fabricated and characterized with PVA thin films as a gate dielectric. The maximum process temperature was 70°C, which corresponds to a baking temperature of the spin-coated polymeric dielectric. Glass and flexible PET foils were used as substrates. Theses devices showed high performance electrical characteristics and worked at a low operating voltage of − 5 V. The highest field effect mobility of 2.6 cm2/Vs and the lowest threshold voltage of − 1.7 V were obtained on a flexible substrate.

Graft polymerization synthesis and application of magnetic Fe3O4/polyacrylic acid composite nanoparticles

AbstractFe3O4 magnetic nanoparticles were prepared by coprecipitation using NH3 · H2O as the precipitating agent, and were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X‐ray powder diffraction (XRD). The compatibility between the Fe3O4 nanoparticles and water were enhanced by grafting acrylic acid onto the nanoparticle surface. FTIR, XRD, thermogravimetry (TG), and differential scanning calorimetry (DSC) were used to characterize the resultant sample. The effects of initiator dosage, monomer concentration, and reaction temperature on the characteristics of surface‐modified Fe3O4 nanoparticles were investigated. Moreover, magnetic fluids (MF), prepared by dispersing the PAA grafted Fe3O4 nanoparticles in water, were characterized using UV–vis spectrophotometer, Gouy magnetic balance, and laser particle‐size analyzer. The rheological characteristics of magnetic fluid were investigated using capillary and rotating rheometers. The MF was added to prepare PVA thin film to improve mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

CdS Nanoparticles Grown in a Polymer Matrix by Chemical Bath Deposition

Nanocrystallites of CdS have been grown by chemical bath deposition within the pores of poly(vinyl alcohol) (PVA) on glass and Si substrates. The CdS-PVA composite films are transparent in the visible region. XRD and TEM diffraction patterns confirmed the nanocrystalline CdS phase formation. TEM study of the film revealed the manifestation of nano CdS phase formation and the average particles size was varied in the range 5-12 nm. UV-vis spectrophotometric measurement showed high transparency (nearly 80% in the wavelength range 550-900 nm) of the films with a direct allowed band gap lying in the range 2.64-3.25 eV. Particle sizes have also been calculated from the shift of band gap with respect to that of bulk value and were found to be in the range 3.3-6.44 nm. The high dielectric constant (lies in the range 120-250 at high frequency) of PVA/CdS nanocomposite compared to that of pure PVA (-28) has been observed. The dielectric constant decreases with increase of dispersibility of the CdS nanoparticles within PVA. The nanocrystalline PVA/CdS thin films have also showed field emission properties with a turn-on field of approximately 6.6 V/microm, whereas only PVA thin film and bulk CdS on PVA have shown no field emission.

ZnS nanobelts grown in a polymer matrix by chemical bath deposition

Transparent polycrystalline ZnS nanobelts have been grown by chemical bathdeposition within the pores of polyvinyl alcohol on glass and Si substrates. Zincacetate and sodium sulphide, dissolved in an alkaline medium, were taken as thesource of zinc and sulfur respectively. X-ray diffraction and transmission electronmicroscopy studies confirmed the cubic nanocrystalline ZnS phase formation. TEMmicrographs of the films revealed the formation of ZnS nanobelts of width 5–20 nm andlength of a few microns. UV–vis spectrophotometric measurement showed hightransparency (around 80% in the wavelength range 350–800 nm) of the film with a directallowed band gap in the range 4.03–3.90 eV; the band gap decreases with theincrease of deposition temperature. Studies of the dielectric properties showed highdielectric constant (in the range 70–130) compared to only PVA and bulk ZnS thinfilm.

Study of electrical properties for albumin/ poly(vinyl alcohol) blends

AbstractThermally stimulated depolarization current (TSDC), d.c. electrical conductivity (σ), and current–time characteristic techniques were used to study electrical polarization and conduction mechanisms for pure poly(vinyl alcohol) (PVA) and 2.5, 5, 10, 12, 15, and 20 wt % albumin content in PVA thin films. The TSDC spectrum for PVA revealed the existence of two broad peaks, while the blend samples show only one broad peak with a shoulder in the high‐temperature side. The existence of this current maximum was analyzed and discussed in terms of dipole‐orientation and space‐charge phenomena. Quantitative analysis was carried out to determine the thermal activation energies of the conduction process, drift mobility, and carrier concentration. The crystallinty of the PVA matrix was enhanced by the addition of albumin, as indicated by X‐ray diffraction and differential scanning calorimetry (DSC) measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1748–1757, 2003

Resistance to nonspecific protein adsorption by poly(vinyl alcohol) thin films adsorbed to a poly(styrene) support matrix studied using surface plasmon resonance.

Thin films of poly(vinyl alcohol) (PVA) polymer were prepared on a flat, nonporous, poly(styrene) support matrix by adsorption from aqueous solution and were characterized in order to investigate the nonspecific adsorption of proteins to a chromatographically relevant surface. The integrity and surface coverage of the PVA thin films were established by surface analysis and atomic force microscopy imaging. The adsorption of the PVA polymers to the poly(styrene) substrate and the nonspecific adsorption of proteins to the PVA-coated surface were monitored using surface plasmon resonance. PVA was strongly bound to the poly(styrene) surface, but the surface density of the adsorbed PVA polymers was affected substantially by the concentration, molecular weight, and degree of hydrolysis of PVA polymers used. There was evidence of increasing degrees of unfolding of the PVA polymer onto the poly(styrene) surface as the concentration of the the PVA coating solution increased. Complete PVA coverage of the poly(styrene) surface was observed at PVA concentrations of 0.1 mg/mL or greater but with significant influence of both molecular weight and degree of hydrolysis of the PVA polymers. Resistance of the PVA-coated poly(styrene) surface to the nonspecific adsorption of human serum albumin (HSA) correlated with the degree of surface coverage of the PVA. The use of anti-HSA as a probe for adsorbed HSA suggested that HSA was displacing PVA from the poly(styrene) surface at the lower PVA surface coverage. A complete barrier to nonspecific protein adsorption was observed with a PVA coating solution concentration of greater than 0.1 mg/ mL with a degree of hydrolysis of <88%.