Templated growth of superparamagnetic iron oxide nanoparticles by temperature programming in the presence of poly(vinyl alcohol)

Magnetite (Fe₃O₄) nanostructures with different morphologies including uniform nanoparticles, magnetic beads and nanorods were synthesized via a co-precipitation method. The synthesis process was performed at various temperatures in the presence of polyvinyl alcohol (PVA) at different concentrations. It is shown that small amounts of PVA act as a template in hot water (70 °C), leading to the oriented growth of Fe₃O₄ nanorods, which was confirmed by selected area electron diffraction. Individually coated magnetite nanoparticles and magnetic beads were formed at a relatively lower temperature of 30 °C in the folded polymer molecules due to the thermo-physical properties of PVA. When a moderate temperature (i.e. 50 °C) was used, nanorods and nanobeads co-existed. At higher concentrations of PVA (polymer/iron mass ratio of 5), however, the formation of magnetic beads was favored. The nanorods were shown to be unstable upon exposure to electron beams. Freezing/thawing process was applied post synthesis as temperature programming to fabricate stable nanorods with rigid walls.     

Gold nanoparticles reinforced poly (vinyl alcohol) of self-standing optical films

A simple one-step process is developed to synthesize self-standing optical films of Au-doped polymer of poly(vinyl alcohol) (PVA). The visible color could be tuned precisely over a wide range from the violet to a yellowish with selective Au-contents from 0.1 to 5.0 wt%. The synthetic procedure involves a caloric Au3+ --> Au reaction in aqueous PVA at 60-90 degrees C temperatures followed by casting the sample (Au-nanocrystals (NCs) embedding in the PVA polymer molecules) as films or other shapes. Stable color persists of nanocolloids as well as films. The NCs are thin platelets of triangular, square, rectangular, or hexagonal shapes. There are very few pentagonal platelets and nanorods. As analyzed with microstructure, the NCs formation results in a structural anisotropy by the preferential adsorption of PVA on selective facets. An Au-content dependent emission occurs in the 400-650 nm regions, useful for possible optical data storage, nonlinear optical devices, and color pigments.     

Biocompatibility of poly(vinyl alcohol)-hyaluronic acid and poly(vinyl alcohol)-gellan membranes crosslinked by glutaraldehyde vapors

Glutaraldehyde (GTA) solutions are commonly used to crosslink biomolecules and artificial polymers in order to reduce the degradation rate and to avoid the rapid dissolution in biological fluids. The toxicity of these materials is often due to the presence of GTA residuals unremoved by washing procedures. In this study membranes of PVA-hyaluronic acid and PVA-gellan with different composition have been obtained by solution casting technique and crosslinked by exposure to vapors of GTA in acid environment. The harmful effects of GTA residuals released from the membranes have been evaluated by the cytotoxicity and cytocompatibility in vitro tests, based on the cell culture method. The results showed that these materials have no toxic effects: they do not affect cell viability and proliferation, nor exert damages on mithocondrial and lysosomal functions. The poor adhesion of cells seeded directly onto membranes is due to the surface properties of these materials which are completely refractory at cell adhesion and proliferation. The use of GTA in vapor phase as crosslinking agent of natural and artificial polymer blends is demonstrated to be an efficacious procedure that avoids the presence of toxic residuals into materials.     

Chitosan/poly (vinyl alcohol) films containing ZnO nanoparticles and plasticizers

In this study ZnO nanoparticles were prepared by the Pechini method from a polyester by reacting citric acid with ethylene glycol in which the metal ions are dissolved, and incorporated into blend films of chitosan (CS) and poly (vinyl alcohol) (PVA) with different concentrations of polyoxyethylene sorbitan monooleate, Tween 80 (T80). These films were characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), swelling degree, degradation of films in Hank's solution and the mechanical properties. Besides these characterizations, the antibacterial activity of the films was tested, and the films containing ZnO nanoparticles showed antibacterial activity toward the bacterial species Staphylococcus aureus. The observed antibacterial activity in the composite films prepared in this work suggests that they may be used as hydrophilic wound and burn dressings.     

硫酸酯化聚阴离子PVA的合成及表征

硫酸与聚乙烯醇(PVA)经酯化制备PVA聚阴离子电解质.分别考察了反应时间、反应温度等对取代度的影响.采用红外光谱(IR)、扫描电镜(SEM)对硫酸酯化PVA聚阴离子电解质的结构进行了表征,测定了其热稳定性和导电性.     

One-step preparation of poly(vinyl alcohol)-protected Pt nanoparticles through a heat-treatment method

A heat-treatment method for the preparation of well-stable, polymer-protected Pt nanoparticles in the range of 2-7 nm in diameter is demonstrated. The formation of Pt nanoparticles occurs in a single step process, carried out by heating an aqueous solution containing a poly(vinyl alcohol) polymer and H₂PtCl₆, with the use of PVA to serve as both a reducing reagent and a protective reagent. The Pt nanoparticles were characterized by UV-vis absorption spectra, transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS) and the Pt nanoparticle formation process was further investigated by in situ UV-vis experiment.     

Poly(aniline-co-m-aminobenzoic acid) deposited on poly(vinyl alcohol): Synthesis and characterization

In this work, we have deposited poly(aniline-co-m-aminobenzoic acid) on poly(vinyl alcohol) (PVA) by in situ polymerization. The polymerization was effected within maleic acid (MA) cross-linked PVA hydrogel. The copolymer was obtained by oxidative polymerization of aniline hydrochloride and m-aminobenzoic acid using ammonium persulfate as an oxidant. Instead of conventional solution polymerization, here synthesis was carried out on APS soaked MA cross-linked PVA (MA–PVA) film where the polymer was in situ deposited in its conducting form. The composite film was characterized by Fourier transform infra red (FT–IR) and ultraviolet visible (UV–VIS) spectroscopy and electrical measurements. Surface morphology of the composite films was studied by field emission scanning electron microscopy (FESEM). The variation of conductivity of the films was studied.     

Facile one-pot synthesis of iron oxide nanoparticles cross-linked magnetic poly(vinyl alcohol) gel beads for drug delivery

In this paper, a facile one-pot strategy for scalable synthesis of robust magnetic poly(vinyl alcohol) (mPVA) gel beads is developed. Through dropwise addition of mixed aqueous solution of iron salts and PVA solution into alkaline (e.g., ammonia, NaOH, and KOH) solution, mPVA gel beads with uniform size and excellent superparamagnetic property can be fabricated based on the simultaneous formation of magnetic iron oxide nanoparticles (MIONs) and cross-link of PVA chains. Moreover, this approach can be extended to prepare dual- or multiresponsive gel beads through simply adding functional fillers into PVA solution (e.g., mPVA-PNIPAM gel beads that possess both magnetic and temperature responsibilities can be readily prepared by adding temperature responsive poly(N-isopropylacrylamide) (PNIPAM) into PVA solution). It is found that that the obtained mPVA gel beads exhibit high drug loading level (e.g., above 70%) after the treatment of freezing-thawing. Drug release experiments reveal that the drug release rate and amount of the mPVA gel beads can be tuned by operating the external magnetic field and adjusting the concentration of iron oxide nanoparticles and temperature (for mPVA-PNIPAM gel beads). The present work is of interest for opening up enormous opportunities to make full use of magnetic gel beads in drug delivery and other applications, because of their facile availability, cost-effective productivity, and tunable drug release performance.     

Synthesis and characterization of nanofiber webs of chitosan/poly(vinyl alcohol) blends incorporated with silver nanoparticles

Nanofiber webs of chitosan (CS)/poly(vinyl alcohol) (PVA) blends incorporated with silver nanoparticles (AgNs) were fabricated by two different methods: a refluxing method and an annealing method. We found that the characterization and antibacterial activity of AgNs depended on not only the fabrication methods but also the weight ratio of CS and PVA in the CS/PVA blend. The change in the size and number of AgNs due to the interaction between AgNs and CS, in turn, affected the antibacterial property of the non-woven webs. Non-woven webs of CS/PVA nanofibers containing AgNs that were fabricated by the refluxing method showed higher antibacterial ability against Escherichia coli than did the other types of non-woven webs. The morphology of the electrospun non-woven webs was observed by field emission scanning electron microscopy. The characterization of AgN formation on the surface of electrospun fibers was examined by transmission electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy.     

Synthesis of silver nanoparticles in poly(vinyl alcohol) matrix in solution and thin films through laser irradiation

Here we communicate our experimental results on the synthesis of silver nanoparticles in solution and thin films using silver nitrate and poly vinyl alcohol (PVA) mixture at different concentrations and different laser irradiations. Detailed studies were carried out by varying pulse width, wavelength, exposure time, and energy of the laser. Formation of nanoparticles was confirmed through color change from transparent to yellow. Irradiated solutions and thin films at different concentrations showed plasmon peak in the absorption spectra. Formation of different sized nanoparticles at different energies with peak shift is observed. Transmission electron microscope (TEM) results confirmed the formation of nanoparticles with size of the particles varying from 2 to 200 nm. Formation of silver nanoparticles with hexagonal and different shapes were observed in particular with 355 nm laser irradiation. Influence of wavelength, pulse width, exposure time, and energy in the synthesis of silver nanoparticles is highlighted. Electron diffraction patten of a single nanoparticle in TEM showed polycrystallinity with cubic nature for the silver nanoparticles prepared. We also compared the linear and nonlinear absorption properties of the freshly prepared nanoparticles with nanoparticles solution left in a shelf for a long period of time.     

Self-assembled amphiphilic polyhedral oligosilsesquioxane (POSS) grafted poly(vinyl alcohol) (PVA) nanoparticles

In the present study, spherical nanoparticles (NPs) containing polyhedral oligosilsesquioxane (POSS) as an inner hydrophobic core and poly(vinyl alcohol) PVA as a hydrophilic outer shell were prepared by dialysis approach. Preparation of amphiphilic POSS-grafted-PVA co-polymer was characterized by ¹H NMR and FT-IR. The results indicated urethane linkage between monoisocyanate group of POSS macromer and the hydroxyl groups of PVA. The dynamic light scattering (DLS) and electrophoretic light scattering (ELS) of the NPs revealed that they have an average hydrodynamic diameter and negative zeta (ζ)-potential of 215 nm and ? 161 mV, respectively. Atomic force microscopy (AFM) and bio-transmission electron microscope (BIO-TEM) have shown unagglomerated NPs within a diameter range of 60–90 nm. The prepared NPs were investigated to improve the control release of anticancer drug; paclitaxel as a model drug. Due to drug loading, the hydrodynamic diameter and negative zeta (ζ)-potential have changed to 325 nm and ? 14 mV, respectively. In addition, in-vitro drug release experiments were conducted; the obtained results explicated continuous release for over 40 days. However, in case of using pure drug only, the drug completely released within 1 h.     

Preparing ZnS nanoparticles on the surface of carboxylic poly(vinyl alcohol) nanofibers

This paper presents a new synthetic route to hybridize ZnS semiconductor nanoparticles and poly(vinyl alcohol) (PVA) based electrospinning nanofibers. At first, zinc ions are introduced onto the surface of carboxylic PVA nanofibers. Then sulfide ions are added to react with zinc ions to form ZnS nanoparticles. The average diameter of the nanofibers is about 300 nm, and the diameter of the ZnS nanoparticles is about 5 nm. The photoluminescence spectrum of ZnS/carboxylic PVA nanocomposites has a 60 nm blue shift compared with that of the corresponding bulk ZnS sample. The carboxylic PVA enhances the quantum effects of the ZnS nanoparticles.     

Preparation of CuS nanoparticles embedded in poly(vinyl alcohol) nanofibre via electrospinning

Poly(vinyl alcohol) (PVA)/CuS composite nanofibres were successfully prepared by electrospinning technique and gas-solid reaction. Scanning electron microscopic (SEM) images showed that the average diameter of PVA/CuS fibres was about 150–200 nm. Transmission electron microscopy (TEM) proved that a majority of CuS nanoparticles with an average diameter of about 15–25 nm are incorporated in the PVA fibres. X-ray diffraction (XRD) analyses and electron diffraction pattern also revealed the forming of CuS crystal structure in the PVA fibres.     

Gel-drawn fibres of poly(vinyl alcohol)

Semi-crystalline gels of several samples of poly(vinyl alcohol) were made from solutions in which the polymer concentration varied from 2.0 to 15.0%. Entanglement density in the material was in this way reduced from the melt entanglement density. When gels were partially dried and drawn isothermally the maximum draw ratio increased with drawing temperature up to 11 to 14 at 140 to 180 C. A meltcast film could be drawn to 6.8 times at 140 C. Drawn material had a crystallinity of 55 to 80%, while that of isotropic material was 20 to 55%. Gels of lower initial concentration (lower entanglement density) could be drawn to greater extensions at a given draw temperature and had better mechanical properties. Young's modulus increased with draw ratio to values very close to those for polyethylene fibres drawn by the same amount. Young's modulus was independent of drawing temperature or degree of crystallinity, but on comparing drawn gels of the same draw ratio, crystallinity and crystalline orientation, those of lower entanglement density had a higher Young's modulus.     

Preparation and magnetic behavior of carbon-encapsulated iron nanoparticles by detonation method

Carbon-encapsulated iron (Fe@C) nanoparticles with core/shell structure have been successfully synthesized by detonation method, using a homemade composite explosive precursor. The detonation reaction was ignited by a non-electric detonator in nitrogen gas in an explosion vessel. The as-prepared detonation products were characterized by X-ray Diffraction, Transmission electron Microscopy, Raman spectroscopy and X-ray fluorescence. The magnetic behavior of the Fe@C materials was measured by vibrating sample magnetometer. The results showed that the detonation products were made up of the body centered cubic iron core and the graphitic carbon shell, of which the core diameter was in the range of 15–50 nm. Raman spectroscopy indicated that both graphitic and amorphous carbon occured in the outside shell structures. The hysteresis loops showed the as-made Fe@C nanoparticles were of superparamagnetic at 300 K temperature. A detonation reaction mechanism was proposed to explain the growth process of Fe@C nanoparticles based on these results.     

Fabrication of aligned poly (vinyl alcohol) nanofibers by electrospinning

Electrospinning has become a versatile tool for fabricating nanofibers from materials of diverse origins. Normally, mats of randomly-aligned fibers were obtained. A number of techniques have been proposed to arrive at uniaxially-aligned fibers. This work reports a new technique, i.e., dual vertical wire technique, for fabrication of uniaxially-aligned fibers. This technique utilized two stainless steel wires that were vertically set in a parallel manner between a charged needle and a grounded collector plate. This technique allowed simultaneous collection of aligned fibers (between the parallel vertical wires) and a randomly-aligned fiber mat (on the collector plate). Application of the technique on poly(vinyl alcohol) (PVA) to prepare uniaxially-aligned fibers was found to be successful at short collection times. Unexpected formation of a large fiber tow consisting of individual as-spun nanofibers that were bound into a bundle was observed at long collection times. Morphological appearance and size of the fiber tow was affected by the change in the distance between the two vertical wire electrodes, while the average diameter of the individual fibers was not (i.e., about 340 to 350 nm). Lastly, mechanical properties and thermal behavior of the fiber tow were also investigated.     

Effect of citrate on poly(vinyl pyrrolidone)-stabilized gold nanoparticles formed by PVP reduction in microwave (MW) synthesis

Colloidal PVP (poly(vinyl pyrrolidone))–stabilized gold nanoparticles (PVP–AuNPs) are synthesized in aqueous solution with PVP as a reducing and stabilizing agent using a short microwave (MW) heating duration of 1 min. The size and uniformity of the synthesized PVP–AuNPs can be varied by modifying the concentration of sodium citrate (Na₃Ct), which acts predominantly as mediator of the stability of PVP–AuNP formation during the rapid synthesis. Due to the increase in the Na₃Ct concentration, the number of citrate ions adsorbed on the growing surface of AuNPs increase, and less reactive gold solute complexes are formed, leading to slow stable reactions that produce small, uniform colloidal PVP–AuNPs. We therefore demonstrate that by adjusting the Na₃Ct concentration used in the PVP reduction, the diameter of PVP–AuNPs was varied from 19.47 ± 3.97 nm to 7.94 ± 0.14 nm when using constant concentrations of chloroauric acid (HAuCl₄) and PVP.     

The actuation of a biomimetic poly(vinyl alcohol)poly(acrylic acid) gel

Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as biomimetic actuators and "artificial muscles". In previous work, a thermodynamically consistent finite-elastic constitutive model has been developed to describe the mechanical and actuation behaviours of active polymer gels. The mechanical properties were characterized by a free-energy function, and the model uses an evolving internal variable to describe the actuation state. In this work, an evolution law for the internal variable is determined from free actuation experiments on a poly(vinyl alcohol)poly(acrylic acid) (PVAPAA) gel. The complete finite-elastic/evolution law constitutive model is then used to predict the response of the PVA-PAA gel to isotonic and isometric loading and actuation. The model is shown to give relatively good agreement with experimental results.     

Preparation and characterization of chitosan/poly(vinyl alcohol)/poly(vinyl pyrrolidone) electrospun fibers

Ultrafine fibers of chitosan/poly(vinyl alcohol)/poly(vinyl pyrrolidone) (CS/PVA/PVP) were prepared via electrospinning. The structure and morphology of CS/PVA/PVP ultrafine fibers was characterized by the Fourier transform infrared (FT-IR) spectroscope and scanning electron microscope (SEM). Furthermore, the effects of the concentration of PVA, PVP and the electrospinning voltage on the morphology of ultrafine fibers were investigated the the SEM. When the concentration of PVA was at the range of 30wt%–40wt%, ultrafine fibers could be obtained. The diameter distributions of ultrafine fibers decreased when the electrospinning voltage increased from 20 to 30 kV. The rough surface fibers could be obtained after etching with CHCl₃.     

Polyaniline microrods synthesized by a polyoxometalates/poly(vinyl alcohol) microfibers template

Polyaniline (PAn) microrods doped with H₄SiW₁₂O₄₀ (HPA) were obtained by a H₄SiW₁₂O₄₀/Poly(vinyl alcohol) microfibers template method. The morphology of the polyaniline microrods was observed by scanning electron microscope (SEM) photograph. The average diameter of the polyaniline microrods was between 200 and 250 nm. IR spectra and X-ray diffraction characterized the structure of the polyaniline doped with H₄SiW₁₂O₄₀. The conductivity of the polyaniline microrods was measured by a four-probe method. The highest conductivity of the polyaniline microrods was 3.9 S/cm.