Polyvinyl Alcohol Molecules Research Articles

Adsorption Characteristics of Polyvinyl Alcohols in Solution on Expanded Graphite

Expanded graphite (EG) adsorbent was prepared with 50 mesh graphite as raw materials, potassium permanganate as oxidant, and vitriol as intercalation compound. Three kinds of polyvinyl alcohol (PVA) with different degree of polymerization (DP) in aqueous solution were used as adsorbates. We have studied the influence of initial PVA concentration, temperature and ionic strength on adsorption capacity. Langmuir constants and Gibbs free energy change (⊿G°) were calculated according to experimental data respectively. Thermodynamic analysis indicates the equilibrium adsorbance of PVA on EG increase with the rise of SO42– concentration. Adsorption isotherms of PVA with different degree of polymerization are all types and we deduce PVA molecules lie flat on EG surface. Adsorption processes are all spontaneous. Kinetic studies show that the kinetic data can be described by pseudo second‐order kinetic model. Second‐order rate constants and the initial adsorption rate rise with the increasing of temperature and half‐adsorption time decreases with the increasing of temperature. The adsorption activation energy of each PVA is less than 20 kJ•mol−1, physical adsorption is the major mode of the overall adsorption process.

Molecular dynamics simulation on surface modification of carbon black with polyvinyl alcohol

A novel and reasonable model of carbon black (CB) was built to investigate the surface encapsulation modification of CB particles with polyvinyl alcohol (PVA) by molecular dynamic simulation. The modification process of PVA on CB surface was intuitively exhibited, which indicated that the encapsulation films were formed by stacking PVA molecules layer by layer on the surface of CB. The dispersion stability of unmodified and modified CB particles was compared both by simulation and by scanning electron microscope graphs. The simulation results indicated that surface modification had great effect on reducing the interaction energy of CB/water interface so as to alleviate agglomeration phenomenon significantly. Moreover, the influences of PVA amount on the morphology and the compatibility of PVA/CB interface were also investigated. The amount of PVA would neither influence the arrangement of single PVA molecule nor change the orientation of the single PVA layer but only decide the thickness of the modification film. Besides, the energy analysis results indicated that a suitable thickness of PVA coating could improve the dispersion stability of CB particles.

Size variation of polyaniline nanoparticles dispersed in polyvinyl alcohol matrix

We report the preparation of polyaniline (PANI) nanoparticles dispersed in polyvinyl alcohol (PVA) matrix. From SEM picture it is seen that the particle sizes vary from 100–20 nm. Also with increase in PVA content the stability of dispersion is found to increase. Apart from SEM, spin cast films of PANI in PVA are also characterized through XRD and FTIR. XRD shows increase in crystallinity with PVA content and FTIR gives evidence of crosslinking between PANI and PVA molecules. In plane electrical conductivity (in the range of 102 Scm−1) and the exponent of nonlinear I–V are found to decrease with increase of PVA content. There is a good correlation between SEM, XRD, FTIR and electrical properties.

A high-resolution solid-state NMR study on starch–clay nanocomposites and the effect of aging on clay dispersion

High-resolution solid-state nuclear magnetic resonance (NMR) was applied as a bulk analysis method to provide an indication of clay dispersion in starch–clay nanocomposites. The starch composite containing 2.5 wt% nano-clay appeared as an exfoliated system with an average distance between clay platelets (<D̄>) of around 40 nm. Increasing the amount of nano-clay to 5.0 wt% reduced the <D̄> value to around 20 nm. Aging displayed a minimal effect on the exfoliation of starch–clay nanocomposites. However, the <D̄> value became much larger on introduction of 5 wt% polyvinyl alcohol (PVOH) into the systems because of the formation of aggregated structures, and the <D̄> value increased further after aging. The motion of PVOH molecules during the aging period could function as a driving force toward a more stable interaction between PVOH chains and clay platelets, thus resulting in a reduction in the degree of clay exfoliation in the starch matrix. The high-resolution solid-state NMR technique was applied as a bulk analysis method to provide an indication of nano-clay dispersion in starch–clay nanocomposites. The effects of having polyvinyl alcohol as additives and aging up to 105 days were also investigated.

Structural and magnetic properties of polymer-stabilized tetragonal Ni nanoparticles

Ni nanoparticles (Ni-NPs), with diameter (D) ranging 5–30 nm, were synthesized by reducing nickel chloride with NaBH4 in the presence of polymer molecules of poly-vinyl alcohol (PVA) in cold water. Nickel chloride was dispersed in the PVA molecules which stabilized the resulting Ni-NPs. Experiments were carried out with and without PVA to elucidate the effect of PVA molecules on the structural and magnetic properties of Ni-NPs. It was found that both uncoated (uc) and PVA-coated (pc) Ni-NPs exhibit a tetragonal (t) crystal structure, i.e. different from the cubic (fcc) structure of bulk nickel. pc Ni-NPs (paramagnetic in nature) converted to fcc Ni (spherical shape, D ∼ 12 nm) on annealing at 573 K in air, exhibiting a saturation magnetization M s = 20.5 emu/g, squareness ratio M r /M s = 0.48 and coercivity H c = 248 Oe, which is higher than the bulk Ni (0.7 Oe). uc Ni-NPs showed little improvement in M s and H c on air annealing. The core–shell structure resulted in a high H c value in stable pc Ni-NPs in air. Electron magnetic resonance revealed exchange interaction between the core and shell, which changes on annealing in air.

Preparation and thermomechanical properties of Ag-PVA nanocomposite films

Metal–polymer hybrid nanocomposites have been prepared from an aqueous solution of polyvinyl alcohol (PVA) and silver nitrate (AgNO 3). The silver nanoparticles were generated in PVA matrix by the reduction of silver ions with PVA molecule at 60–70 °C over magnetic stirrer. UV–vis analysis, X-ray diffraction studies, transmission electron microscopy, scanning electron microscopy and current–voltage analysis were used to characterize the nanocomposite films prepared. The X-ray diffraction analysis reveals that silver metal is present in face centered cubic (fcc) crystal structure. Average crystallite size of silver nanocrystal is 19 nm, which increases to 22 nm on annealing the film at 150 °C in air. This result is in good agreement with the result obtained from TEM. The UV–vis spectrum shows a single peak at 433 nm, arising from the surface plasmon absorption of silver nanocolloids. This result clearly indicates that silver nanoparticles are embedded in PVA. An improvement of mechanical properties (storage modulus) was also noticed due to a modification of PVA up to 0.5 wt% of silver content. The current–voltage ( I– V) characteristic of nanocomposite films shows increase in current drawn with increasing Ag-content in the films.

Synthesis, mechanical and I –V characteristics of Ag–PVA nanocomposite films

AbstractHybrid polymer–inorganic nanocomposites have been prepared from an aqueous solution of polyvinyl alcohol (PVA) and silver nitrate (AgNO3). The silver nanoparticles have been generated in PVA matrix by reduction of silver ion with PVA molecules at 60–70 °C over a magnetic stirrer. X‐ray diffraction studies, UV–visible analysis, transmission electron microscopy, scanning electron microscopy and current–voltage analysis were used to characterize the nanocomposite films prepared. The X‐ray diffraction studies showed that silver metal is present in a face‐centered cubic (fcc) crystal structure with average crystallite size 19 nm, which grows to 22 nm on annealing the film at 150 °C in air. This is in good agreement with the result obtained from TEM. The UV–visible spectrum shows a single peak at 433 nm, arising from the surface plasmon absorption of silver colloids. This result clearly indicates that silver nanoparticles are embedded in PVA. An improvement of mechanical properties (storage modulus) was also noticed due to a modification of PVA up to 0.5 wt% of silver content. The current–voltage (I–V) characteristics nanocomposite films obey Ohm's law and the current drawn increases with increasing Ag content in the films. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Study on the Polyvinylalcohol/Montmorillonite Composite Hydrogel

A series of alkyl ammonium/montmorillonite (MMT) were compounded with polyvinyl alcohol (PVA) to prepare the composite hydrogel with improved water absorbency and mechanical property. The effect of the nature of the surfactants on the intercalation of PVA chains within the silicate galleries, the interfacial compatibility and the properties of the composites was studied. A proper type and content of MMT can increase the glass transition temperature, and enhance the swelling behavior and the mechanical properties of the composites. In order to investigate the interaction of the molecules of PVA with water, the state of water in the hydrogel was studied.

Iron oxide nanoparticle-assisted arsenic removal from aqueous system

Iron oxide nanoparticles (IONPs) can play a significant role in the cycling of heavy metals. Arsenite [As(III)] is highly toxic, mobile, and predominant species in arsenic-contaminated groundwater. IONPs have been synthesized and tested for the removal of As(III) from arsenic contaminated water. In this work, we synthesized IONPs, as a finely divided loose nanopowder, using a chemical method involving a dispersion of the metal cations (Fe3 +) through polymer molecules of polyvinyl alcohol (PVA) in an aqueous medium. X-ray diffraction (XRD) analysis confirmed the formation of a single phase rhombohedral crystal structure of R3c space group. Transmission electron microscopic images corroborate the result of IONPs of 45 nm average size and the rhombohedral shape. Selective experiments, conducted with an initial concentration of 0.25 ppm of As(III), have demonstrated the maximum As(III) adsorption capacity (96%) in 2.0 gL− 1 IONPs in water at pH 4.5–7.5. At room temperature, the adsorption isotherm studies have revealed a better correlation with the Langmuir isotherm than the Freundlich isotherm. Characteristic surface hydrolysis of IONPs as = Fe-OH species has been studied in terms of the vibration bands. The results reveal that the removal of the As(III) species from water is associated with the As(III) adsorption onto the IONPs followed by a surface hydrolysis of the iron species.

Phase behavior and properties of polyvinyl alcohol/gelatin blends with novel pH-dependence

A novel change of phase behavior and properties of polyvinyl alcohol (PVA)/gelatin blends as a function of pH was reported. The PVA/gelatin blends were found to be completely miscible in acidic condition (pH 8), and immiscible in neutral condition (pH was ca. 6). As a result, the membranes cast from acidic condition showed the highest tensile strength and the lowest alcohol vapor permeation (AVP) rate; those obtained from neutral condition showed the lowest tensile strength and highest AVP rate; the properties of membranes cast from basic condition lay in between. The interaction between PVA and gelatin was investigated via Fourier transform infrared spectrum (FTIR), differential scanning calorimetry (DSC), and Zetasizer measurement. The novel pH-dependence of the blends was ascribed to the protonation of amino groups of gelatin in acidic condition, which resulted in a strong electrostatic attraction between NH of gelatin and OH of PVA. The partial miscibility in basic condition was due to the ionization of carboxyl groups of gelatin, which caused a stretching of gelatin via electrostatic repulsive force and a breakage of the H-bonding among the molecular chains, leading to a limited interaction between PVA and gelatin and forming a partially miscible blend. In neutral conditions, there were almost no charges (very limited protonation and ionization) at the weak polyampholyte gelatin, and the strong H-bonding among gelatin molecules themselves or PVA molecules themselves caused the phase separation between gelatin and PVA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 239–247, 2009

BaTiO3 nanoparticles of orthorhombic structure following a polymer precursor. Part I. X-ray diffraction and electron paramagnetic resonance

BaTiO3 nanoparticles were synthesized from a polymer template of Ba2+ and Ti4+ ions embedded in polymer molecules of polyvinyl alcohol. The polymer burns off upon heating in air at temperature as high as 450°C, resulting in a Pnma orthorhombic crystal structure for pure BaTiO3 (o-BT-II). Distinct peaks appear in the X-ray diffractogram after 2 h of heating the sample at 550°C, with lattice parameters a = 0.6435 nm, b = 0.5306 nm, c = 0.8854 nm, and density ρ = 5.124 g cm−3. The usual tetragonal phase with a = 0.3994 nm, c = 0.4038 nm, and ρ = 6.012 g cm−3 appears as early as 650°C, with average crystallite size (D) growing as large as 25 nm from a value of 15 nm after 550°C. Two electron paramagnetic resonance signals occur for g ∼ 2.00 and 4.30 due to interstitial oxygen , or vacancies , and modified Ti4+ → Ti3+ (3d 1) especially in the surfaces of small particles.

Shape-controlled silver metal of nanospheroids from a polymer-assisted autocombustion reaction in open air

Abstract Nanospheroids of silver, D = 18–27 nm diameters, have been synthesized following an autocombustion reaction of a polymer complex of polyvinyl alcohol (PVA) containing Ag + → Ag species in open air. It is shown that, when heating with Ag + species in water, PVA molecules induce a local Ag + → Ag reaction, forming such a complex of Ag-nanoparticles dispersing in situ in the PVA molecules. A viscous sample (hot) could be cast and dried in 3–5 wt.% Ag-PVA films (50–100 μm thickness) at room temperature. Ag metal of nanospheroids occurs upon heating 5–10 mm pieces of the films over 300–500 °C in air. According to the X-ray diffraction, it has an Fm 3 m cubic crystal structure. After 300 °C, the sample consists of small crystallites ( D = 24 nm), with the lattice parameter a = 0.4071 nm (density ρ = 10.618 g/cm 3 ), which relaxed nonlinearly to a value 0.4085 nm ( ρ = 10.509 g/cm 3 ) upon D -value growing to be as large as 27 nm over higher temperatures.

A new allotropic structure of silver nanocrystals nucleated and grown over planar polymer molecules

Polymer molecules of polyvinyl alcohol (PVA) serve as a good Ag+ → Ag0 reducer as well as a template to produce Ag0 nanocrystals of anisotropic shapes. Thin Ag–PVA films (50–100 µm thick) were prepared by carrying out the reaction in aqueous PVA (under heating conditions) and then spin casting the sample in this shape. A topotactic Ag+ → Ag0 reaction and in-situ Ag0 growth occur in support over the PVA molecules (as per the local structure and Ag0–PVA interactions) of elongated surfaces. The Ag0 state is confirmed with 3d 5/2 and 3d 3/2 XPS signals of 368.37 and 374.13 eV binding energies, respectively. As analyzed with X-ray diffraction, it is a new allotrope with an orthorhombic structure, lattice parameters a = 0.8535, b = 0.8410 nm and c = 0.4119 nm, and density ρ = 9.69 g cm−3. On heating in air, the well-known cubic structure develops, a = 0.4082 nm (ρ = 10.53 g cm−3) after 150°C, whereas a = 0.4071 nm (ρ = 10.61 g cm−3) after 300°C for 2 h. According to proposed models, it is a vacancy-stabilized allotrope, which evolves from multiply twinned particles.

Nanorods of Silver-Coated Magnetic CrO2 Particles from a Polymer Template in Hot Water

A surface coating of silver of CrO2 nanoparticles at an early stage of growth leads the latter to grow in an anisotropic shape of nanorods. When heating in polymer molecules of polyvinyl alcohol (PVA) in water at ∼90 °C fibrils as long as 10−50 μm (∼300 nm diameter) have developed embedding in the polymer. Small PVA molecules, which disperse with elongated molecular surfaces in the water, template a directional growth of nanorods. The CrO2 fibril reinforced (3−5 wt %) polymer of freestanding films could be made. X-ray diffraction confirms the fibril microstructure, i.e., a preferred [001] growth of CrO2 uniting in the (110) domains. The template that imposes a shear stress over the growing species in a cluster supports the species uniting and growing along the surface (template). The lattice parameters have smaller values, a = 0.4415 and c = 0.2945 nm with an improved density ρ = 4.88 g/cm3, in comparison to those of the virgin sample, a = 0.4429 and c = 0.2950 nm (ρ = 4.84 g/cm3), in the tetragonal structure. We found that the CrO2 clusters can be made magnetoresistive and stable in ambient air by adding a thin metallic Ag layer.

Effect of composition on the formation of poly(dl-lactide) microspheres for drug delivery systems: Mesoscale simulations

In this work, the structure–property relationship of drug delivery systems (DDS) is investigated by dissipative particle dynamics (DPD) simulations. Nifedipine is selected as the model drug, whereas poly(dl-lactide) (PLA) as the carrier and polyvinyl alcohol (PVA) as the stabilizer. It is shown from DPD simulations that PLA, drug, and PVA could aggregate and form microspheres under a defined composition recipe; drug molecules are amorphously and homogeneously distributed inside the carrier matrix, on whose surface the stabilizer PVA molecules are adsorbed. Under different compositions of each component, aggregate morphologies of the oil phase are observed as spherical, columnar, and lamellar structures. A phase diagram of DDS has been proposed, which could be used to guide the experimental preparation of DDS with desired properties. © 2007 Elsevier B.V. All rights reserved.

A simple polyol synthesis of silver metal nanopowder of uniform particles

Silver metal has been synthesized in form of a finely divided loose nanopowder, 10–30 nm particle sizes, using a simple polyol process. In hot water, polymer molecules of polyvinyl alcohol (PVA) induce Ag + → Ag reaction as a weak reducer (suitable to control the final particle size), forming a nanofluid of Ag nanoparticles in situ dispersing in part of PVA molecules. Ag nanoparticles do not aggregate much when casting a viscous Ag–PVA nanofluid (hot) onto a substrate in thin laminates or films. Freestanding Ag–PVA films could be obtained of 1–5 mm thickness after drying at room temperature. Dried sample can be easily peeled from a silicate glass substrate. As small as 5–10 mm Ag–PVA pieces were heated in air in order to recollect Ag nanoparticles by burning off the polymer. At 300–400 °C, Ag–PVA disintegrates and encounters combustion in air, resulting in a pure Ag-powder. As analyzed by X-ray diffraction, a single crystalline phase of an Fm3 m cubic crystal structure formed. Lattice parameter a = 0.4071 nm and density ρ = 10.61 g/cm 3 compare well the bulk values a = 0.4086 nm and ρ = 10.50 g/cm 3.

Rheology and structure of aqueous bentonite-polyvinyl alcohol dispersions

The influence of polymer on flow behaviour of Balikesir, Turkey bentonite dispersions (2%, w/w) was studied for non-ionic polymer, polyvinyl alcohol (PVA). In a range of 3.3 × 106 −3.3 × 105 mol/l, PVA was added to the bentonite dispersions in different concentrations and its behaviour was observed on rheology parameters. Thixotropy was detected by a hysteresis loop of the flow curves. The data were interpreted taking into account the interactions of colloidal clay particles, bentonitic clay concentrations, structure, and concentrations of added PVA. The particle size analysis was explained by surface orientation of PVA to the clay particles dispersed in aqueous solution. Zeta potential determination also emphasized that PVA molecules got attached on the face and edge surface of clay particles. The morphology of bentonite dispersions was analysed by scanning electron micrograph (SEM). FTIR studies carried out in parallel to rheology studies showed that hydrogen bonds were formed between surface of the clay, and absorbed PVA molecules and adsorbed water. The presence of PVA did not prevent extensive swelling of bentonite.

Gold Nanoparticles from Induced Au3+→Au0 Reaction in Polyvinyl Alcohol Molecules in Presence of Sucrose in Hot Water

In hot water (50–60°C), polyvinyl alcohol (PVA) molecules have coordination reaction with Au3+ cations, forming an Au3+-PVA polymer complex. In the proposed model reaction in small templates, the complex converts to Au0 capping in PVA molecules. Adding sucrose (5–10 times the PVA in mass) in a typical batch promotes Au3+→Au0 reaction, showing absorption coefficient α in Au0 surface plasmon band to be enhanced as much as 28 times the value in reaction with PVA. The band shifts at 547 nm from 566 nm (α = 21.4 cm−1 mol−1) in the PVA sample. Drying Au0-PVA/sucrose (2–5 wt% Au0) colloid at 60–70°C and then heating at 450°C in air burns off the organic part, leaving behind a light ash colored powder with Au0 nanoprisms or nanofibrils (∼30 nm average width). X-ray diffractogram has six reflections, (111), (200), (220), (311), (222), and (400), of Fm3m fcc Au0 of lattice parameter a = 0.4080 nm. The powder has photoluminescence in transversal and longitudinal Au0 plasmon bands of 535 and 585 nm, respectively.

Biodegradation of polyvinyl alcohol by a mixed microbial culture

A mixed culture capable of degrading 1 g l −1 polyvinyl alcohol (PVA) completely was screened from sludge samples at Pacific Textile Factory, Wuxi, China. This mixed culture had stronger capability of degrading PVA with low polymerization and high saponification than degrading PVA with high polymerization and low saponification. Inorganic nitrogen source was more suitable for the mixed culture to grow and degrade PVA than organic nitrogen source. Microorganisms and relative abundance of this mixed culture were explored by terminal restriction fragment length polymorphism (T-RFLP). Small PVA molecules were detected in cell extracts of the mixed culture. This indicated that PVA degradation in the mixed culture was in fact a combined action of extracellular and intracellular enzymes. Two strains producing extracellular PVA-degrading enzyme were isolated from the mixed culture. They could individually degrade PVA1799 with polymerization of 1700 from initial average molecular weight 112,981 to 98,827 Da and 84,803 Da, respectively. However, only small amount of PVA124 in polymerization of 400 could be degraded by these two strains.

Microstructure, topology and X-ray diffraction in Ag-metal reinforced polymer of polyvinyl alcohol of thin laminates

A polymer composite of Ag-metal reinforced polyvinyl alcohol (PVA) is synthesized in shape of thin laminates of 200–300 μm thickness. The process involves a chemical Ag+ dispersion in PVA and in-situ \({\rm Ag}^{+} \to {\rm Ag}\) reduction-reaction with active PVA molecules under hot conditions (with stirring) in water at 60–70°C temperature. The product results in a metal Ag-polymer complex dispersed in the solution. After evaporating part of water, a derived viscous solution is casted (in hot conditions) in shape of a thin laminate in a glass mould. In addition to chemical reducer, active OH-groups (free from H-bonding) in PVA molecules of refreshed surfaces act as head groups to adsorb Ag+ and drive a directional \({\rm Ag}^{+} \to {\rm Ag}\) growth. Short fibrils of Ag-metal thus occur in reaction over the PVA molecules. Casting thin laminates from a liquid sample Ag-PVA allows the fibrils (also the polymer molecules) to align along the surface. Selected Ag-contents up to 5.0 wt.% in Ag-PVA laminates are studied in terms of scanning electron micrograph, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Average size, morphology and aspect ratio (ϕ) vary in Ag-metal depending on the Ag-content. As long Ag-metal fibrils as 2–5 μm, ϕ=35, occur in a sample of 2.0 wt.% Ag. The Ag-metal reflects in two characteristic 3d5/2 and 3d/3/2 XPS bands of 368.3 and 374.1 eV respectively.