Radiolitička sinteza i karakterizacija PVA/Au nanokompozita – uticaj pH rastvora

Nanokompoziti polimer - nanočestice plemenitih metala predstavljaju važnu grupu nanomaterijala. Njihova svojstava zavise kako od veličine nanopunioca, tako i od načina sinteze nanokompozita. U radu su radiolitički, gama zračenjem sintetisani koloidni rastvori PVA/Au, pri različitim pH vrednostima, od kojih su uparavanjem rastvarača dobijeni nanokompozitni filmovi. UV-Vis apsorpcioni spektri rastvora imaju karakterističnu plazmonsku apsorpciju nanočestica zlata na oko 520 nm. Vrednosti maksimuma apsorpcije su nelinearno zavisne od pH vrednosti rastvora. Talasna dužina maksimuma apsorpcije je najmanja za pH = 7, što teorijski odgovara česticama najmanje veličine. Dimenzije čestica su određene i XRD merenjima. Interakcija nanopunioca i matrice praćena je IC spektroskopijom, a termička stabilnost nanokompozita je ispitana TG analizom

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

Synthesis and physicochemical evaluation of new chitosan-based scaffolds for potential application in biomedicine

Chitosan is a natural polymer obtained by deacetylation of chitin. Due to its biocompatibility and biodegradability, chitosan-based materials have a wide range of biomedical applications in wound dressings, drug delivery systems, and tissue engineering. Also, studies in the fields of organic and medicinal chemistry show that compounds based on the pyridone core exhibit biological properties including antimicrobial, anticancer, and antioxidant activity, and moreover have the potential as new therapeutics for various diseases from cardiovascular to antitumor therapy. In this study, new biomaterials were synthesized using low and medium molecular weight chitosan polymers and pyridone-based hydrazone. In order to improve stability of the obtained scaffolds, scaffolds’ neutralization was carried out using ethanol and sodium hydroxide solutions. The interactions established between chitosan polymer chains and pyridone compound were analyzed by FT-IR spectroscopy. Swelling and degradation tests of the materials were studied in water and PBS, and the influence of different polymer molecular weights on the scaffolds’ properties was evaluated. The results indicated that synthetized scaffolds have a high potential for biomedical use

Cyclic voltammetry study of electrochemically synthesized Ag/PVP nanocomposite

Hydrogel nanocomposites of silver nanoparticles (AgNPs) and crosslinked poly(N-vinyl-2- pyrrolidone) (PVP) were synthesized in situ by a novel electrochemical method. PVP hydrogels, crosslinked by gamma-irradiation, were swollen in the solution containing 0.1 M KNO3 and 3.9 mM AgNO3. PVP polymer matrix nanocavities were used as nanoreactors for AgNPs synthesis. The reduction of silver cations was performed using two-Pt-electrode electrochemical cell. The polarity of the electrodes was changed on the half of the implementation time, enabling the Ag+ ions reduction in the bulk. Cyclic voltammetry (CV) was performed in a three-electrode electrochemical cell, using the saturated calomel electrode (SCE) as a reference. Ag/PVP nanocomposites were scanned by CV immediately after the synthesis and after drying followed by reswelling in 0.1 M KNO3. Ag/PVP was compared with CVs of the following systems: Pt electrode in 0.1 M KNO3; Pt/PVP system in 0.1 M KNO3; Ag/Pt system in 0.1 M KNO3 + 3.9 mM AgNO3 solution.Belgrade, Serbia, June 6-10, 2010Related to the published paper in the Proceedings of the Second Regional Symposium on Electrochemistry South-East Europe, [http://cer.ihtm.bg.ac.rs/handle/123456789/3523

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

Improvement of Au-poly(N-isopropylacrylamide) hydrogel nanocomposites: Singlelayer vs. bi-layered systems

In recent years, the need for innovative materials has produced remarkable progress in the field of smart materials, with a particular focus on nanocomposite systems containing crosslinked polymer matrices (hydrogels) and metal nanoparticles. Hydrogels have become a crucial class of biomaterials due to their stable 3D porous structures, high fluid absorption capacity, similarity to biological tissues, and biocompatibility. Of particular interest are hydrogels with the ability to respond to various external stimuli (temperature, pH, light etc.), resulting in alterations of their physical and chemical characteristics. Our research focuses on the nanocomposites based on thermosensitive poly(N-isopropylacrylamide) (PNiPAAm) hydrogels and gold nanoparticles (AuNPs), with a unique emphasis on exploring the specific properties of single-layer and bi-layered systems. The insights gained from this comparative study open new possibilities for applications in drug delivery, sensors, and soft robotics. Single-layer systems consisting of active PNiPAAm hydrogel and AuNPs, were created through a combination of radiolytic and chemical procedures. Bi-layered systems feature an active Au-PNiPAAm layer, with the addition of a passive poly(vinyl alcohol) (PVA) hydrogel layer, crosslinked by the combination of freeze-thaw and radiolytic techniques. In both cases, the incorporation of spherical AuNPs within an active layer was confirmed by the presence of a characteristic surface plasmon resonance (SPR), while scanning electron microscopy (SEM) indicated the system's highly porous structure. The physicochemical properties of both single- and bi-layered systems involved the examination of their swelling and deswelling properties, as well as the volume phase transition temperature (VPTT). The incorporation of AuNPs in the PNiPAAm layer led to an increase in both swelling capacity and VPTT. Compression measurements showed that the presence of a passive layer and AuNPs significantly improved mechanical properties of nanocomposites.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Hydrogel nanocomposite photoactuator for direct optical to mechanical energy conversion obtained by ionizing irradiation

The incorporation of suitable nanomaterials into the stimuli responsive hydrogel matrix enables the hydrogel nanocomposites to become a key soft component of new generation of soft electronic and soft robotic devices1,2. An energy transformation agent, functional gold nanoparticles and nanorods exhibit unique photo-thermal properties as a result of a surface plasmon resonance electron-phonon process and intrinsic inter-band transitions. Upon immobilization in thermo-responsive hydrogel, they induce local photo-thermal shrinking under visible light irradiation and thus enable external wireless remote control of hydrogel device and programmable photo-thermo-mechanical motion. In addition, in this way control of interface conductivity can be realized by switching hydrogel nanocomposites between electrically communicating and non-communicating states. In this work, a soft photo/thermal reversible hydrogel nanocomposite device consisting of gold nanoparticles or nanorods embedded in poly(N-isopropylacrylamide) (PNIPAM) and poly(Nisopropylacrylamide) (PNIPAM)/poly(vinyl alcohol) (PVA) bilayer structure (in order to maximize shape changes), were developed using nanotechnology based on radiation chemistry. The key parameters deciding the actuation characteristics as well as conductivity and percolation threshold, particle diameter and shape as well as interparticle distance, can be easily tailored during synthesis using radiation processing technology. Obtained hydrogel nanocomposite device with wireless remote actuation and electrical control has great potential for lightharvesting and mechanical motion which is required for the construction of soft smart actuator systems for applications in soft robotics, for dense information storage and efficient energy conversion.International Conference on Advances in Functional Materials; August 18-20, Los Angeles, 2021.Symposium 4: Functional Composite Materials (FCM