Multiwalled carbon nanotube nucleated crystallization and reinforcement in poly (vinyl alcohol) composites

One of the fastest growing areas of nanotube research is the study of polymer-nanotube composite materials. These materials utilize the excellent strength of carbon nanotubes that has been evident but difficult to harness in the past and show impressive increases in strength relative to the polymer. It is suspected that many of the physical properties observed in these composites are related to the formation of crystalline polymer coatings around the nanotubes in solution. The work presented here addresses this issue by doping a semi-crystalline polymer, poly (vinyl alcohol), with multiwalled carbon nanotubes. Dynamic mechanical analyzer (DMA) measurements of thin films identified a three- to five-fold increase in the Young's modulus of the polymer depending on nanotube type. Dynamic differential scanning calorimetry (DSC) of thin films shows that the increase in modulus is accompanied by an increase in polymer crystallinity. In addition, the results verify that multiwalled carbon nanotubes nucleate crystallization of the polymer and a link between polymer crystallinity and composite reinforcement is established. Furthermore, transmission electron microscopy (TEM) images confirm an excellent dispersion and wetting of the nanotubes in the polymer solution providing visual evidence of matrix reinforcement.     

A study on the preparation of poly(vinyl alcohol) nanofibers containing silver nanoparticles

In this study, two practical methods for the facile and controlled preparation of poly(vinyl alcohol) (PVA) nanofibers containing Ag nanoparticles were investigated for use in antimicrobial applications. In the first method, PVA nanofibers containing Ag nanoparticles were successfully electrospun from PVA/silver nitrate (AgNO₃) aqueous solutions after first refluxing them. The Ag nanoparticles in the PVA/AgNO₃ aqueous solutions were generated by refluxing them. Interestingly, it was found that the Ag nanoparticles were also spontaneously generated during the electrospinning process. In the second method, Ag nanoparticles were generated by annealing the PVA nanofibers electrospun from PVA/AgNO₃ aqueous solutions. Residual Ag⁺ ions and the Ag nanoparticles generated during the electrospinning process in the PVA nanofibers were diffused and aggregated into larger Ag nanoparticles during the annealing process. All of the Ag nanoparticles were sphere shaped and evenly distributed in the PVA nanofibers prepared by the two methods.     

Composite films of nanostructured polyaniline with poly(vinyl alcohol)

The uniform composite films of nanostructured polyaniline (PANI) (e.g. nanotubes or nanorods with 60–80 nm in diameter) were successfully fabricated by blending with water-soluble poly(vinyl alcohol) (PVA) as a matrix. The PANI nanostructures were synthesized by a template-free method in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. The molecular structures of PANI–β-NSA and the related composite films were characterized by UV–Vis absorption spectrum, FTIR spectrum and X-ray diffraction. It was found that the electrical, thermal and mechanical properties of the composite films were affected by the content of nanostructured PANI–β-NSA in the PVA matrix. The composite film with 16% PANI–β-NSA showed the following physical properties: room-temperature conductivity is in the range 10⁻² S/cm, tensile strength ∼603 kg/cm², tensile modulus ∼4.36×10⁵ kg/cm² and ultimate elongation ∼80%.     

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.     

Alkali doped poly(vinyl alcohol) for potential fuel cell applications

Optical transparent, chemically stable alkaline solid polymer electrolyte membranes were prepared by incorporation KOH in poly(vinyl alcohol) (PVA). The distributions of oxygen and potassium in the membrane were characterized by XRD and SEM–EDX. It is demonstrated that combined KOH molecules may exist in the PVA matrix, which allow it to be an ionic conductor. In particular, the chemical and thermal stabilities were investigated by measuring changes of ionic conductivities after conditioned the membrane in various alkaline concentrations at elevated temperatures for 24 h for potential use in fuel cells. The membranes were found very stable even in 10 M KOH solution up to 80 °C without losing any membrane integrity and ionic conductivity due to high dense chemical cross-linking in PVA structure. The measured ionic conductivity of the membrane by AC impedance technique ranged from 2.75 × 10^?4 S cm^?1 to 4.73 × 10^?4 S cm^?1 at room temperature, which was greatly increased to 9.77 × 10^?4 S cm^?1 after high temperature conditioning at 80 °C. Although, a relatively higher water uptake, the methanol uptake of this membrane was one-half of Nafon 115 at room temperature and 6 times lower than that of Nafion 115 after conditioned at 80 °C. The membrane electrolyte assembly (MEA) fabricated with PVA–KOH in direct methanol fuel cell (DMFC) mode showed an initial power density of 6.04 mW cm^?2 at 60 °C and increased to 10.21 mW cm^?2 at 90 °C.     

Conducting semi-IPN based on polyaniline and crosslinked poly(vinyl alcohol)

In the present course of investigation synthesis and properties of a series of polyaniline–PVA-based semi-IPNs are described. PVA component in a PAn–PVA composite solution/dispersion, prepared by steric stabilization mechanism, was crosslinked to give rise to the present IPN. Formaldehyde was used as the crosslinker and the IPNs were isolated in the form of flexible and free-standing films. Morphological and structural properties of the system were studied from FTIR spectra and SEM images. Different solid state properties, viz. dc conductivity at different temperatures, thermal and mechanical properties and moisture regain were also studied and a series of films with good mechanical and thermal properties were obtained.     

Water-soluble polyaniline and its composite with poly(vinyl alcohol) for humidity sensing

Water-soluble polyaniline (PANi) was prepared by a “green” method with poly (stryrenesulfonic acid) (PSSA) as a template, and characterized by UV–vis spectroscopy, FT-IR spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). It was found that the films of PANi and its composite with poly(vinyl alcohol) (PVA) were composed of nanoparticles. The humidity sensitive properties of the both PANi and its composite with PVA were investigated at room temperature. The water-soluble PANi exhibited high sensitivity (impedance change over three orders of magnitude in the range of 15–97%RH) and good sensing linearity on a semi-logarithmic scale, but a relatively large hysteresis of ～8%RH. In contrast, the composite of PANi and PVA showed a very small hysteresis of ～2%RH. Moreover, the response was fast and highly reversible. The humidity sensing mechanism of the composite of PANi with PVA was explored by measuring its complex impedance spectra under different humidities.     

Conductive films of tetrathiafulvalene dicarboxylate cation radicals and poly(vinyl alcohol) formed by casting

Aqueous solutions of dipotassium tetrathiafulvalene dicarboxylate (1), potassium ferricyanide and poly(vinyl alcohol) were used to cast air-stable, flexible and electrically conductive films. Casting at 80–95 °C formed a network of microcrystals oriented in the film plane. Spectroscopic studies showed that these crystals contain π-stacks of the cation radical 1⁺. No evidence for mixed valence stacks was found. A film containing 5 wt.% of 1⁺ in PVA had a four-point conductivity σ = 10⁻² S cm⁻¹ in the film plane. The structural anisotropy led to a lower conductivity (10⁻⁴ S cm⁻¹) across the plane of the film.     

Non-woven fabric of poly(N-isopropylacrylamide) nanofibers fabricated by electrospinning

We have succeeded in fabricating non-woven fabric of a typical thermo-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) with a low critical solution temperature (LCST) in water at 32 °C, by the electrospinning, a simple and facile method which enables to form a mat of nanofibers directly deposited on the grounded target. The PNIPAM nanofibers electrospun at concentration and applied voltage of 15 wt% and 20 kV, respectively, had an average diameter of 165 nm. The moisture sorption isotherms of the PNIPAM nanofibers belonged to the type II of IUPAC classification, in which the interaction between polymer and water molecule was stronger than that between water molecules.     

Influence of absorbed moisture on solubility of poly(vinyl alcohol) film during atmospheric pressure plasma jet treatment

Moisture in the hydrophilic material may potentially influence the plasma treatment effect. In order to understand how moisture absorbed into PVA affects the result of plasma treatment to the polymer, atactic poly(vinyl alcohol) (PVA) films with moisture regain (MR) of 2.5%, 9.3% and 78.3% corresponding to 10%, 65% and 98% relative humidity (RH), respectively were exposed to atmospheric pressure plasma jet. Another group was annealed at 140 °C for 20 min to discern the thermal effects from those due to plasma treatment. Scanning electron microscope (SEM) showed lamellae crystal structures were on the surface of the films with 65% and 98% RH, while some bubbles or salt grains appeared on the surface of film with 10% RH and the annealed film respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that oxygen concentration increased for plasma treated films with 65% and 98% RH and decreased for that with 10% RH. X-ray diffraction analysis (XRD) shows an increase in crystallinity in all the plasma treated films. It was found that the solubility of all the treated films was decreased, especially for the plasma treated film under 98% RH which is nearly insoluble in water at 50 °C for 20 min.     

Double-walled carbon nanotube (DWCNT)–poly(3-octylthiophene) (P3OT) composites: Electrical,optical and structural investigations

In the present study, we report experiments based on in situ polymerization of 3-octylthiophene with DWCNT and many hitherto unstudied properties for the first time. The specialty of DWCNT being the inner tube retaining its intrinsic electronic and optical properties, while the outer tube could be involved in the composite formation. From the IR aromatic and out-of-plane C–H stretching frequencies, the interaction between the polymer and the nanotubes is probed. Further to this absorption spectroscopy, photoluminescence and Raman measurements were carried out to characterize the composites. The conductivity contributions of the nanotubes and Hall voltage measurements are used to understand the utility of the composites for solar cell applications.     

Fabrication and optical characterization of electrospun poly(3-buthylthiophene) nanofibers

Light-emitting poly(3-buthylthiophene) (P3BT) nanofibers were fabricated via an electrospinning method. Ten weight percent poly(ethylene oxide) (PEO) was included in a P3BT spinning solution to maintain the required viscosity for electrospinning. The formation of P3BT nanofibers was confirmed through high-resolution confocal photoluminescence imaging and spectroscopy and micro-Raman measurements performed on single strands of P3BT nanofibers. Our results show that P3BT nanofibers can be fabricated using the electrospinning method that can produce abundant continuous nanofibers.     

Temperature dependent conductivity and thermoelectric power of the iodine doped poly(vinyl alcohol)–Cu chelate

We have investigated the temperature dependence of electrical conductivity and thermoelectric power (TEP) at 1.7 K < T < 300 K in an organo metallic complex, the iodine doped poly(vinyl alcohol)–Cu²⁺ chelate. We observed intrinsic metallic temperature dependence of resistivity from room temperature to 68 K with a broad minimum [ρ(68 K)/ρ(300 K) 0.75], which has not been observed previously in similar organo metallic complexes. There occurs an unusual metal-insulator transition at T 68 K and the resisitivity increases upon cooling below 68 K. However, the low temperature resistivity becomes finite (instead of going to infinity), [ρ(1.7 K)/ρ(300 K) 0.98] indicating that a quantum mechanical tunneling conduction is dominant at this low temperature. It is remarkable that the resistivity at 1.7 K is as small as that of room temperature. Such unusual temperature dependence of conductivity could be understood as thermally assisted hopping conduction between metallic islands. However, the observed intrinsic metallic temperature dependence of resistivity implies that such hopping conduction barrier is not important at high temperature (T > 68 K). The intrinsic metallic characteristics are confirmed by the quasi-linear temperature dependence of TEP for the whole measured temperature range (1.7 K < T < 300 K) with a small slope change at low temperature, T < 68 K, which is understood as an effect of variable range hopping (VRH) conduction at low temperature. The results of magneto resistance (MR) and magneto thermoelectric power (MTEP) are consistent with the above interpretation.     

Polyaniline-poly(vinyl alcohol) composite as an optical recording material

Conducting polymer image and diffraction grating pattern were recorded in dichromated poly(vinyl alcohol) (DCPVA) films by visible light exposure, in a process resembling photolithography. Aniline, used as a chemical developer, polymerized into the unexposed areas of the DCPVA matrix, yielding a composite material which allowed permanent optical information storage and exhibited optical properties characteristic of polyaniline. The photoreduction properties of the DCPVA films and the optical properties of the composite were studied by UV–VIS spectroscopy. The characterization of the diffraction grating composite gave a line width of 12.15 μm and a diffraction efficiency of 32%.     

XPS studies of environmental stability of polypyrrole-poly(vinyl alcohol) composites

In this paper, we report a study on the aging effects of polypyrrole-poly(vinyl alcohol) composites. A decrease of the conductivity is observed when samples are stored in ambient atmosphere, whereas they are stable in inert environment. A careful analysis of the studied samples has been performed by using both scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is known that oxidation processes occur, breaking the conjugation of the polymeric unsaturated chains and this is the main cause for the non-stability of the composites in ambient conditions. Consequently, several oxygen-containing groups are formed in the polymer backbone, as deduced from the analysis of the C, O, N and Cl binding energies.     

Poly(vinyl alcohol)-colloidal silica composite membranes for fuel cells

The aim of this study is to develop an environmentally and friendly poly(vinyl alcohol) based low cost membrane with improved ionic conductivity, thermal and mechanical stability. In this work, the effect of colloidal silica content on membrane properties was investigated. Sulfosuccinic acid (SSA) was used as the sulfonating agent. In order to enhance the mechanical and ionic conduction properties, colloidal silica was used. The range of silica content in the membrane solution investigated was 5–20%. For the characterizations, the synthesized membranes were subjected to FT-IR, TGA, tensile strength analysis, water uptake, ion exchange capacity (IEC) and impedance measurements for proton conductivity. Synthesized membranes demonstrated high water uptake (up to 80%) without swelling, high ion exchange capacities was found to increase with increasing SSA content. The proton conductivity of CS doped membranes increased with increase in temperature and the temperature dependence showed significant change in the CS doped membranes. An increase in the values of the proton conductivity was driven by the mobility of free charges (free ions) as the temperature was increased. Addition of SSA and CS to the polymer matrix improved the thermal stability of the membranes. It was also discovered that membranes were in a composite structure and colloidal silica particles did not contribute to the structure of the polymer matrix at the molecular level. Mechanical durability of the membranes having SSA content above 15% decreased and these membranes showed a more fragile structure.     

The effect of the carbon nanotubes surface oxidation on the morphology and properties of poly(N-vinylcarbazole) coated multi-walled carbon nanotube nanocables

This article describes the effect of carbon nanotubes (CNTs) outer surface oxidation on the morphology and properties of poly(N-vinylcarbazole) (PNVC)-coated individual multi-walled CNT (MWCNT) nanocables. Surface oxidation of MWCNTs has been carried out by refluxing MWCNTs with 5 M nitric acid (HNO₃) at 80 °C for 1 h. The PNVC-coated MWCNT nanocables are synthesized by in situ solid-state polymerization of N-vinylcarbazole monomers in the presence of oxidised MWCNTs (o-MWCNTs) at an elevated temperature. The PNVC-coated MWCNT nanocables are characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning and transmission electron microscopes, photo-luminescence spectroscopy, and direct-current conductivity measurements. Results show that the uniform nanolayer coating of PNVC decreases the inherent bulk conductivity of MWCNTs, but significantly increases the optical properties of MWCNTs.     

A study of the thermal degradation of poly(vinyl chloride)

A thermal degradation of poly(vinyl chloride) (PVC) was studied. This was an essential step in the investigation of the compatibility of PVC-based systems because mixing in industry and in the preparation of materials is carried out in the viscous flow range close to thermal degradation. Original Russian Text ? K.A. Polozkov, A.E. Chalykh, V.K. Gerasimov, V.V. Matveev, A.D. Aliev, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 5, pp. 537–540.     

Evaluation of nanosilicate filled poly (vinyl chloride-co-vinyl acetate) and epoxy coatings

The corrosion protection, mechanical and thermal properties of nanoclay filled epoxy and poly (vinyl chloride-co-vinyl acetate) (VYHH) resins have been studied. Nanoclay was incorporated into VYHH at 0%, 0.5% and 1.5%wt loadings, and into epoxy at 0% and 1.5% loadings. Steel substrates were prepared and coated with each of the prepared coatings. Some of the samples were submerged in a tank containing 5% NaCl solution and tested periodically using electrochemical impedance spectroscopy (EIS) to study the effect of the nanoclay on the corrosion protection of the coatings. Films were cast from each system to be used to evaluate the mechanical performance of the coatings. Notched and unnotched samples were cut from the films and some were submerged in the 5%NaCl solution while some were left unsubmerged as controlled samples. EIS measurements showed that VYHH/0.5%nanoclay provided superior barrier protection. The nanoclay filled epoxy exhibited increased barrier properties after 21 days. The tearing energy of the neat VYHH coating decrease by 27% after submersion, while the nano coatings showed a slight increase. The neat epoxy showed no change in the tearing energy after submersion, while that of the nano coating was increased by 14% after submersion. Differential scanning calorimetry (DSC) results showed that the nano coatings have improved the thermal barrier properties compared to the neat.