Thermal properties of radiolytically synthesized PVA/Ag nanocomposites

The radiolytic method was used to synthesize two types of nanocomposites with silver, PVA/Ag by film casting and PVA hydrogel/Ag nanocomposites. This method is particularly suitable for generating metal nanoparticles in solution. The radiolytic species (solvated electrons and secondary radicals) exhibit strong reducing properties such that metal ions are reduced at each encounter. Metal atoms then tend to grow into larger clusters. It was found that solid or swollen polymers are able to stabilize small crystallites against spontaneous growth via aggregation. Using differential scanning calorimetry (DSC), the melting behavior and kinetics of the PVA/Ag nanocomposites were investigated and compared to those of pure PVA. The melting as well as crystallization behavior of polymers is crucial because it governs the thermal properties, impact resistance and stress strain properties. Understanding the melting behavior is significant not only to tailor the properties of nanocomposites but to investigate the interactions between the constituents. The DSC curves of pure PVA and prepared nanocomposites show only one melting peak between 175 and 230 degrees C, indicating that the melting behavior of these two systems are analogous. In both cases, with increasing heating rate, the melting peak shifts to a higher temperature, but with increasing Ag content the peak melting temperature is lower. When specimens are heated at high heating rate, the motion of PVA molecular chains cannot follow the heating temperature on time due to the influence of heat hysteresis, which leads to a higher peak melting temperature. When Ag nanoparticles are added they increase the heat transfer among the PVA molecular chains decreasing the melting temperature. The Ag content is a major factor affecting the degree of crystallinity. It was observed that at low nanofiller content, up to the 0.5 wt%, the degree of crystallinity of the nanocomposites increased, while at a higher content the crystallization was retarded. The half time of melting is non-linearly dependent on the amount of nanofiller. In the range from 0.25 to 1 wt% Ag it slightly increases, because at a low Ag content the nanoparticles act as a heterogeneous nucleation agent during the crystallization process. For large amounts of nanofiller, the half time of melting is markedly higher than for pure PVA. At a higher Ag content, the nanoparticles act as a barrier that restricts the thermal motion of PVA molecular chains and the half time of complete melting increases. The significantly lower melting activation energy of the nanocomposites with high amount of nanofiller compared to pure PVA, calculated by the Kissinger method, indicated that nanoparticles reduced the heat barrier for the melting process.5th Young Researchers Seminar, Dec 25-26, 2006, Belgrade, Serbi

Radiolytic synthesis and characterization of PVA/Au nanocomposites: The influence of pH values

Nanocomposites which consist of polymer matrix and nanoparticles of noble metal are a very important class of nanomaterials. The optical properties of these materials are strongly dependent on the nanoparticles size as well as on the synthesized procedure of nanocomposites preparation. In this work the Au nanoparticles were synthesized by the simple radiolytic procedure, using steady state gamma irradiation, under different pH values. PVA/Au nanocomposite films were obtained by solvent evaporation from Au colloids. UV-Vis absorption spectra of Au colloids show absorption in the range of 450 to 650 nm with the maximum around 520 nm, which is the typical plasmon band of Au nanoparticles. Absorption spectra of PVA/Au nanocomposites are red shifted compared to corresponding primary Au colloids. This red shift is not result of any change in particle size distribution and can be explained by the change of dielectric property of surrounding medium. IR spectra indicated anchoring the OH groups of PVA molecule at the cluster surface. This effect limits the growing of the metal clusters and confirmed that the PVA is a god matrix for in situ synthesis of Au nanoparticles. The size of Au nanoparticles is dependent on the experimental conditions. Obtained results indicated that the pH value of solution played an important role. The values of absorption maximum were not dependent on the concentration of Au3+ cations, but show strong dependence on the pH value of the initial solution. The increase of pH value reduced the mean diameters of nanoparticles. The lowest value of lambda(max) was obtained for colloid with pH 7, which theoretically corresponds to the nanoparticles with minimum dimension. These results are in agreement with the XRD measurement of PVA/Au nanocomposite films and theoretical calculations. According to obtained results of radiolytic synthesis of Au nanoparticles in PVA solution can be conclude that it is possible to control the particle size by tuning the pH value of solution.6th Conference of Young Researchers, Dec 24-26, 2007, Belgrade, Serbi

Non-isothermal dehydration of equilibrium swollen radiolytically sinthesized Fe3O4 – PVA ferrogel nanocomposite

In this study, the Fe3O4 - PVA ferrogel nanocomposite was synthesized by gamma irradiation. Obtained ferrogel had greater swelling capacity and activation energy of dehydratation as measured by thermogravimetric analysis under non-isothermal conditionsPhysical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200

Swelling behavior of Ag/PVA hydrogel nanocomposite synthesized by γ-irradiation

In this study, the Ag/PVA hydrogel nanocomposite was synthesized using γirradiation. Incorporated Ag NPs were less than 10 nm in diameter with face centered cubic (fcc) crystal structure. Incorporation of Ag NPs into PVA hydrogel significantly affects the characteristic parameters of swelling process

Non-isothermal kinetics of dehydration of Ag/PVA hydrogel nanocomposite synthesized by Γ-irradiation

In this study, the non-isothermal kinetics of dehydration of γ-radiolytically synthesized PVA and Ag/PVA nanocomposite hydrogels was investigated by thermogravimetric analysis (TGA). Kinetic analysis was performed by applying different model fitting and model-free kinetic analysis to estimate kinetic parameters, the activation energy (Ea) and pre-exponential factor (A). The analysis showed that incorporation of silver nanoparticles (Ag NPs) into PVA hydrogel matrix has influence on kinetic parameters of dehydration process.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

Gamma irradiation induced synthesis of PbS/PVA hydrogel nanocomposite

This work describes radiolytic in situ incorporation of lead sulfide nanoparticles (PbS NPs) in poly(vinyl alcohol) (PVA) hydrogel. Optical, structural, swelling and diffusion properties of prepared PbS/PVA hydrogel nanocomposite were investigated. Obtained results indicate formation of PbS NPs with a cubic crystal structure and diameter around 3 nm. Incorporation of PbS NPs in PVA hydrogel causes a change in the swelling and diffusion properties

Poly(NiPAAm-co-IA) hydrogels synthesized by y-irradiation: swelling behavior in water

In this study, N-isopropylacrylamide/itaconic acid copolymeric (poly(NiPAAm-coIA)) hydrogels were synthesized by γ-irradiation induced simultaneous polymerization and crosslinking of monomers. The influence of comonomer concentration (IA) on the swelling behavior in water was investigated. The results showed that values of network parameters increase with an increase of IA, and that the swelling transport mechanism is a non-Fickian transport.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

Influence of the irradiation conditions on the effect of radiation on polyethylene

Two types of polyethylene, low density (LDPE) and high density (HDPE), as well as low density polyethylene containing an antioxidant were subjected to gamma-irradiation in the presence of air and in water. The irradiated polymers were studied using IR spectrophotometric analysis. The radiation induced oxidative degradation was followed through the formation of oxygen containing groups by the development of bands in the 1850-1650 cm(-1) region and double bonds formation by the development of bands in the 1050-850 cm(-1) region. The crosslinking efficiency was determined by measuring the gel content by extraction with xylene. The radiation induced changes in the molecular structure, evolution of oxygen containing species and formation, of vinyl double bonds as well as of the crosslinking efficiency are discussed in terms of the properties of the polymers in an electric field of low strength

Electroanalytical Sensing of Bromides Using Radiolytically Synthesized Silver Nanoparticle Electrocatalysts

Monitoring bromides (Br-) is of crucial importance since bromates, potential human carcinogens, are formed during ozonation of water containing bromides in concentrations GT 100 mu gL(-1). Within this study, silver (Ag) and four carbon-supported Ag catalysts were synthesized by the gamma-radiation method and their morphology and structure examined using transmission electron microscopy, X-ray diffraction, and UV-Vis analysis. The nanocatalysts were tested for Br- sensing in aqueous media using cyclic voltammetry. All five Ag materials exhibited electroactivity for sensing of Br- ions, with pure Ag catalyst giving the best response to Br- ions presence in terms of the lowest limit of detection. Sensing of bromides was also explored in tap water after addition of bromides suggesting that herein prepared catalysts could be used for bromides detection in real samples. Furthermore, sensing of other halogen ions, namely, chlorides and iodides, was examined, and response due to chloride presence was recorded

Mass spectrometric investigation of silver clusters

Silver clusters were produced by two different synthesis procedures, related with different reduction species. PVA (polyvinyl alcohol) was successfully utilized as a source to reduce silver (Ag) metal ions without using any additional reducing agents to obtain Ag clusters. Silver clusters with atoms numbering 5-29 are registered through mass spectrometry using MALDI TOF and MALDI TOF/TOF techniques. Analysis showed that clusters with magic numbers are the largest, while those with an odd number of atoms are larger than clusters with an even number of atoms. Stability of these molecules, magic number actually, is in relation with their electronic configuration