Metal nanocomposite films prepared in situ from PVA and silver nitrate. Study of the nanostructuration process and morphology as a function of the in situ routes

Cast‐hybrid films composed of polyvinyl alcohol (PVA) and silver nitrate were treated according to three different ways, thermal annealing, UV‐irradiation, and chemical reduction by a borohydride solution, to obtain PVA/silver nanocomposite films. The nanostructuration process was studied as a function of the treatment conditions, and discussed as a function of the mobility state of the polymer chains in the nanocomposite matrix during treatment. A homogeneous dispersion of crystalline silver nanoparticles was obtained by thermal annealing above T_g and below T_m and UV‐lamp irradiation below T_g. For these two treatments, the major processing parameters were the annealing temperature and time and the UV‐exposure time, respectively. For low‐conversion rate in Ag(0), the films evolved upon ageing at room temperature. Totally different morphology and Ag(0) conversion were achieved by chemical reduction in a borohydride solution. All the silver ions were reduced into Ag(0), and crystalline silver nanoparticles layers parallel to the film surface were observed after the treatment. This morphology was related to the high‐swollen state of the polymer matrix during treatment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2062–2071, 2008     

十聚钨酸/聚乙烯醇导电膜的制备

最近发现粉状白钨酸在聚乙烯醇(PVA)或其它高分子水溶液中有相当大的溶解度,可以得到稳定的十聚钨酸溶液,并进而得到含十聚钨酸的高分子薄膜。通过光谱鉴定和组成分析,证明了在聚乙烯醇存在下,十聚钨酸能以固态形式存在,而且这是首例十聚钨酸/高分子复合物,并且还研究了组成、湿度、光致变色对复合物薄膜导电性的影响。     

Structure and dielectric relaxations of antibacterial sulfonated polystyrene and silver nanocomposites

Structure and dielectric relaxations of antibacterial sulfonated polystyrene (SPS) and silver nanocomposites (SPS/Ag) were investigated via broadband dielectric spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, differential scanning calorimetry, scanning electron microscopy, and wide‐angle X‐ray diffraction. SPS/Ag nanocomposites were prepared from SPS containing 2, 4, and 7 mol% of acid contents, followed by ion exchange and a reduction process. Silver nanoparticles were formed in the structural cavities of SPS films. The single glass transition temperature of the SPS copolymers was observed and increased with increasing acid contents and more enhanced with embedded silver nanoparticles because of the restriction of the polymer chain movement. The particle size of embedded silver nanoparticles was about 10 nm and well dispersed in SPS matrices. Four dielectric relaxations were observed above the glass transition temperature, and they were attributed to the fast segmental relaxation, the slow‐hindered segmental relaxation, relaxations associated with Maxwell–Wagner–Sillars interfacial polarization and electrode polarization. Weak local relaxations were observed due to the motion of sulfonated phenyl groups. Copyright © 2014 John Wiley & Sons, Ltd.     

Transport of water in polyvinyl alcohol films: Effect of thermal treatment and chemical crosslinking

Data on sorption and transport of water in polyvinyl alcohol films, modified by thermal treatment above T_g, or by chemical crosslinking with glutaraldehyde at different crosslinking degrees, are presented. Equilibrium swelling is constrained by both treatments, except for low degrees of crosslinking where the said reduction is counterbalanced by the partial loss of crystallinity. Analysis of the resulting water uptake kinetics indicates that viscous relaxation effects are, at least partly, responsible for the observed non-Fickian kinetic behavior. Thermodynamic diffusion coefficients of water, D_W, and relaxation frequencies of the swelling polymer, β_W, are determined by application of a theoretical model accounting for relaxation-dependent sorption kinetics in glassy polymers. The results indicate that the effect of both heat-treatment and chemical crosslinking is more intense on the macromolecular relaxation process than on the diffusion coefficient of water. Comparison of the release kinetics of a model drug from as-prepared, non-crosslinked and from crosslinked matrices indicate that the retardation of macromolecular relaxations process induced by crosslinking results in a more uniform release rate.     

Photoacoustic spectroscopic studies of Ho3+, Er3+, and Sm3+ doped polyvinyl alcohol films

Photoacoustic (PA) spectra of Ho³⁺, Er³⁺, and Sm³⁺ doped PVA films were obtained in 350–800 nm range. PA spectra were also obtained for the respective dopant oxides: Ho₂O₃, Er₂O₃, and Sm₂O₃ for comparison. It was found that in PVA the PA sensitivity has increased considerably compared to pure rare earth oxides. The relative intensities of absorption bands at 540 and 637 nm of Ho₃₊: PVA have shown distinct enhancement, indicating the increase in nonradiative relaxation at these excitations. Furthermore, the PA signals at wavelengths for different PA absorption bands were monitored as a function of chopping frequency. These experiments have shown that PA signal varies w⁻¹ both for oxides and PVA samples, suggesting that they behave as thermally thin samples. © 1997 John Wiley & Sons, Inc.     

Shape memory hybrid based on polyvinyl alcohol and 0D silver nanoparticles

Shape memory hybrids (SMH) have drawn significant attention because they allow an easy alternative for the design of shape memory materials with tailored properties or features. In this work, a shape memory hybrid was made, based on polyvinyl alcohol (PVA) as the elastic domain and 0D silver nanoparticles (Agnps) as the transition domain, a dissolution method of mixing both components, and evaporation of water afterward allowed the formation of films of the hybrid material. Two different size distributions of silver nanoparticles were used (13.7 ± 2.6 and 67.9 ± 14.1 nm), in order to study the effect of the size on the shape memory effect (SME) of the final SMH, under temperature stimuli. The materials obtained were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy, infrared spectroscopy (IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The crystallinity of PVA was slightly altered with the addition of Agnps. Finally, the shape memory effect was tested on both hybrid materials, resulting in a better response to temperature for the SMH prepared with Agnps of 68 nm, also the shape recovery time can be tuned varying both the increase of temperature and the size distribution of Agnps used.     

Heterogeneity of laser‐irradiated films of polyvinyl alcohol/starch blends: effect of glycerol content

The present paper reports the results of studies on the effect of laser irradiation on the morphology and thermal properties of starch/polyvinyl alcohol (PVA) blend, with varying glycerol concentration. Differential scanning calorimeter results showed that laser irradiation increased the heat of fusion (ΔH_fus), heat of crystallization (ΔH_cry), temperature of melting (T_m), temperature of crystallization (T_cry) and percentage crystallinity as a function of the amount of glycerol. It is believed that breakdown of the intermolecular hydrogen bonding between the starch and PVA causes an increase in the blend heterogeneity. These results are corroborated with the findings from thermogravimetric analysis and scanning electron microscope images. Copyright © 2013 John Wiley & Sons, Ltd.     

Preparation and properties of silver nanocomposite fabrics with in situ-generated silver nano particles using red sanders powder extract as reducing agent

Nanocomposite cotton fabrics with in situ-generated silver nanoparticles (AgNPs) were prepared by using Pterocarpus santalinus (Red sanders) extract in water as a reducing agent. The formation of AgNPs was analyzed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy. The SEM analysis of nanocomposites showed the presence of spherical AgNPs with a size range of 71–90?nm. FTIR spectra showed the involvement of hydroxyl and methylene groups of cellulose matrix in reducing the silver salt into AgNPs in the presence of red sanders powder extract as reducing agent for the in situ generation of AgNPs. These nanocomposite fabrics exhibited good antibacterial activity against Gram positive and Gram negative bacteria.     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Synthesis,characterization and antibacterial properties of a novel nanocomposite based on polyaniline/polyvinyl alcohol/Ag

In this study, a novel nanocomposite based on polyaniline/polyvinyl alcohol/Ag (PANI/PVA/Ag) has been successfully synthesized. The chemical reduction method was used to produce Ag nanoparticle colloidal solution from Ag⁺ ions. The polymerization of aniline occurred in situ for the preparation of polyaniline (PANI) in the presence of ammonium persulfate. With exposure to Ag nanoparticles on the PANI/PVA composite, a new nanocomposite was obtained. The morphology and particle size of the novel nanocomposite was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) analyses. According to XRD analysis, the size of nanoparticles was found to be in the range of 10–17 nm. SEM images showed the favored shape of nanoparticles as triangle which is a benign shape for antibacterial analysis. The antibacterial activity of the obtained nanocomposite was also evaluated against Gram positive bacteria Staphylococcus aureus (Staph. aureus) and Gram negative Escherichia coli (E. coli) using the paper disk diffusion method. The antibacterial study showed that the PANI/PVA composite did not have a very good antibacterial activity but PANI/PVA/Ag nanocomposites were found to be effective against two bacteria.     

Preparation and characterization of high‐molecular‐weight atactic poly(vinyl alcohol)/sodium alginate/silver nanocomposite by electrospinning

High‐molecular‐weight poly(vinyl alcohol) (PVA)/sodium alginate (SA)/ silver nanocomposite was successfully prepared via electrospinning technique. Water‐based colloidal silver in a PVA/SA blend solution was directly mixing without any chemical and structural modifications into PVA/SA matrix to form an organic‐metallic nanocomposite. The effect of the addition of silver colloidal solution on the PVA/SA/silver nanocomposite was investigated through a series of experiments varying molecular weight of PVA and electrospinning processing parameters such as concentration of PVA solution, PVA/SA blend ratio, applied voltage, and tip‐to‐collector distance. In the case of PVA with number‐average degree of polymerization of 1700, by increasing the amount of SA in spinning solution, the morphology was changed from fine uniform fiber to beaded fiber or bead‐on‐string fiber structure. Increase of the amount of silver colloidal solution resulted in higher charge density on the surface of ejected jet during spinning, thus more electric charges carried by the electrospinning jet. As the charge density increased, the diameter of the nanocomposites became smaller. Transmission electron microscopy images showed that the dense silver nanoparticles were well separately dispersed in PVA/SA matrix. Energy‐disperse X‐ray analysis indicated that carbon, oxygen, natrium, and silver were the principle element of PVA/SA/silver nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1916–1926, 2009     

Synthesis and optical properties of silver nanoparticles and arrays.

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.     

Preparation and characterization of polyvinyl alcohol‐grafted Fe3O4 magnetic nanoparticles through glutaraldehyde

Magnetic nanoparticles (MNPs) are of great interest owing to their numerous existing and potential biomedical applications. To further explore the potential of MNPs in biomedical and other fields, we have designed and synthesized polyvinyl alcohol (PVA) polymer grafted Fe₃O₄ MNPs through glutaraldehyde (GLA) link. The success of this process has been ascertained using Fourier transform infrared (FT‐IR) analysis, thermogravimetric analysis (TGA), X‐ray diffraction (XRD) analysis and scanning electron microscopy (SEM) analysis. The FT‐IR analysis of resultant MNPs show infrared peak characteristics of PVA. TGA analysis clearly shows two major stages of thermal degradation, one corresponding to organic phase of PVA and GLA and another corresponding to Fe₃O₄ nanoparticles. XRD results and SEM images further support the FT‐IR and TGA results and confirm the presence of PVA layer surrounding Fe₃O₄ MNP surface. Under SEM examination, the magnetic cores exhibit somewhat irregular shapes varying from spherical, to oval to cubic. Copyright © 2012 John Wiley & Sons, Ltd.     

Polyethylene-based nanocomposite: Structure and properties of poly(vinyl alcohol)/organofunctionalized Mg-doped fluorapatite hybrid

We report here the production and characterization of polymer nanocomposites (NC)s containing nanoceramics of organofunctionalized Mg-doped fluorapatite (MDFA) in a poly(vinyl alcohol) matrix. First, the MDFA materials were functionalized with N-trimellitylimido-L-leucine modifier through ultrasonic irradiation. The numerous experimental techniques like Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis were applied to characterize the prepared materials. Thermal analysis of the obtained NCs showed an increase in thermal stability of the NCs when compared to the neat macromolecule.     

Emission characteristics of laser dyes C1 and Rh6G in cross-linked polyvinyl alcohol solutions

The lifetimes and the relative quantum yields for fluorescence of two laser dyes Coumarin 1 and Rhodamine 6G have been determined in cross-linked polyvinyl alcohol matrix. The cross-linking has been achieved using gamma radiation. The relative fluorescence quantum yields of the dyes increased with increasing cross-linking of the polymer, but the fluorescence lifetimes remained unchanged within experimental error. The results have been attributed to a reduction in the loss of the excitation energy via the internal conversion of the excited singlet state due to increase in the viscosity of the medium brought about by the increased cross-linking of the polymer.     

Nanocomposites of genipin-crosslinked chitosan/silver nanoparticles--structural reinforcement and antimicrobial properties

This study investigates the feasibility of a novel nanocomposite (GC/Ag) of a genipin-crosslinked chitosan (GC) film in which was embedded various amounts of Ag nanoparticles for wound-dressing applications. In situ UV-vis results revealed that adding chitosan solution did not affect the characteristics of Ag nanoparticles. The water uptake ratios and surface hydrophilicity of the GC/Ag nanocomposite were better and the degradation rates slightly lower than those of the pure GC film. The presence of Ag nanoparticles enhanced L929 cell attachment and growth. Its function as an anti-microbial agent in a GC/Ag nanocomposite was assessed for Ag contents of over 100 ppm. In conclusion, silver ions had dual functions--structural reinforcement and provision of antimicrobial properties to a biocompatible polymer.     

Preparation and characterization of polyethersulfone/silver nanocomposite ultrafiltration membrane for antibacterial applications

Antimicrobial ultrafiltration membranes were prepared by coating silver nanoparticles on the surface of polyethersulfone (PES) membranes which were fabricated via phase inversion induced by the immersion precipitation technique, and their morphology and performance were compared with the antimicrobial PES membranes synthesized by adding the silver nanoparticles into the casting solution during the phase inversion process. For this purpose, stable and uniform colloidal solutions of the silver nanoparticles were prepared by chemical reduction of silver salt using fructose and dimethylformamide as a reducing agent. The silver nanoparticles were characterized by ultraviolet–visible spectroscopy, X‐ray powder diffraction and dynamic light scattering analysis. The morphology and surface properties of the prepared membranes were examined by field emission scanning electron microscopy and atomic force microscopy analysis. Moreover, the separation properties, antimicrobial efficiency and amount of silver release from the PES nanocomposite membranes during the cross flow ultrafiltration were determined. The results indicated that the silver content of the coated PES membranes was greater than the membranes fabricated by the solution blending method. Also, the permeation flux of the silver‐coated membranes was similar to the neat PES membranes, while the membranes prepared by the second approach had less flux. The membranes synthesized by both coating and blending methods showed high antimicrobial and bactericidal activity against gram‐negative bacteria such as Escherichia coli and gram‐positive bacteria such as Staphylococcus aureus. Finally, the prepared antimicrobial membranes were successfully used for the ultrafiltration of raw milk to reduce the microbial load during the concentration process. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication and characterization of boric acid-crosslinked ethyl cellulose and polyvinyl alcohol films as potential drug release systems for topical drug delivery

In this study, boric acid (BA) is employed as a crosslinking agent to improve the characteristics of two commonly used polymeric films, ethyl cellulose (EC) and polyvinyl alcohol (PVA), for topical drug delivery applications. The developed films are characterized by FTIR spectroscopy and SEM analysis. The results show that the surfaces of the prepared films are even and transparent, except for the BA-modified EC sample. The initial cumulative release for erythromycin (EM) is found to be 0.30 and 0.36 mg/mL for EC and PVA films, which drops to 0.25 and 0.20 mg/mL after BA crosslinking, respectively, after 1 h at 25 °C. Further, the developed formulations are stable for 75 days. Also, the antibacterial activity of the developed formulations is investigated against S. aureus (ATCC® 25923™ and ATCC® 29213™). The obtained data confirm that the application of BA as the crosslinking agent extends the release of EM from EC and PVA polymeric films. The findings of this study suggest that BA-crosslinked EC and PVA films are promising carriers for controlled topical drug delivery applications.     

Induced birefringence of rubbed and stretched polyvinyl alcohol foils as alignment layers for nematic molecules

Some optical properties of poly (vinyl alcohol) (PVA) films are investigated prior and after the rubbing and stretching of the samples. Birefringence of the prepared foils is enhanced as their stretching degree and rubbing become larger. These processing factors are also affecting the values of the ordinary and extraordinary refractive indices. The induced anisotropy in PVA foils is evidenced in the morphological characteristics observed by optical microscopy. The spreading and adhesion behaviors of a nematic liquid crystal on PVA foils are analyzed by means of contact angle measurements. Preliminary testing of the nematic on the PVA films revealed significant variations in transmitted light intensity during sample rotation under crossed polarizers. The high contrast between dark and bright patterns is indicative of uniform and homogenous alignment of nematic on the rubbed and stretched PVA foils.     

Application of CuO nanoparticles modified with vitamin B1 for the production of poly(vinyl alcohol)/CuO nanocomposite films with enhanced optical,thermal and mechanical properties

In this Investigation, the CuO nanoparticles (NPs) were treated by vitamin B₁ as a biomolecule modifier. The CuO NPs were used as an appropriate filler for fabrication of poly(vinyl alcohol) (PVA) nanocomposites (NCs). Then, NCs with various ratios (3, 5, and 7wt%) of modified CuO were fabricated under ultrasonic irradiation and their properties were compared with pure PVA. Several techniques were used for characterization of NCs. Field emission scanning electron microscopy and transmission electron microscopy analysis indicated that NPs have proper compatibility with the PVA matrix. Thermal gravimetric analysis results confirmed that NCs displayed higher thermal stability than neat PVA. Also, the addition of the NPs into the PVA matrix improved the optical and mechanical behaviors. Finally, the contact angle measurements verified that the hydrophilicity decreased for different ratios of modified NPs loaded in the polymer matrix. Copyright © 2017 John Wiley & Sons, Ltd.