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

Physicochemical characteristics of gamma irradiation crosslinked poly(vinyl alcohol)/magnetite ferrogel composite

Magnetic field sensitive gels, ferrogels, are new promising class of hydrogels. The coupling of hydrogels and magnetic particles has potential application in soft actuators, such as artificial muscles, or for hyperthermia application. In this study, the composite of magnetite particles (Fe3O4) and poly(vinyl alcohol) (PVA) hydrogel is developed using gamma irradiation as a crosslinking agent. PVA and Fe3O4 were chosen due to their well-established biocompatibility, radiation crosslinking potential (PVA), mild magnetic properties and the Curie point near desired heating temperature range (Fe3O4). Physicochemical characteristics of these systems show the effect of the presence of particles in the process of radiation-induced crosslinking. Obtained PVA/Fe3O4 ferrogel composite has greater swelling capacity, activation energy of dehydration and dehydration rate compared to PVA hydrogel, crosslinked under the same conditions

Multisite luminescence of rare earth doped TiO2 anatase nanoparticles

Eu3+, Sm3+ and Tb3+ ions have been incorporated into anatase TiO2 nanocrystals via hydrolytic sol–gel method. Pure anatase phase was confirmed with XRD and TEM measurements. Band gap energies change slightly with rareearth incorporation, from 3.32 eV for undoped TiO2 to 3.15 eV, 3.25 eV and 3.29 eV for Tb3+, Sm3+ and Eu3+doped TiO2. Photoluminescence of Eu3+ and Sm3+ originated from three different sites in TiO2 nanocrystals have been identified with the laser-excited site-selective spectroscopy measurements at 10 K. One site exhibits broad emission peaks, which are ascribed to the distorted lattice site near the surface. Other two sites, associated with the inner lattice, show significantly sharper fluorescence lines as a consequence of an ordered crystalline environment. The emission decays of Eu3+ and Sm3+ have similar values for inner-lattice sites and longer lifetimes for near-surface sites. The luminescence of Tb3+doped TiO2 nanocrystals was immeasurably weak

Gd2O3:Eu3+Gd_{2}O_{3}:Eu^{3+}/PMMA Composite: Thermal and Luminescence Properties

In recent years there is an increasing interest in obtaining and investigating composite materials that comprise nanoparticles as fillers and polymers as matrix. Such composites may display combined features of both components, and sometimes even novel properties resulting from their mutual interactions. It is important that both unique size-dependent properties of nanoparticles and favorable properties of polymer material remain preserved in the composite. In this research we investigated the possibility of obtaining composite material using as polymer matrix poly (methyl methacrylate) - PMMA and $Gd_{2}O_{3}:Eu^{3+}$ nanopowder as filler. Three samples, containing 1, 3 and 5 mass % of $Gd_{2}O_{3}:Eu^{3+}$, are prepared with a dispersion casting method. The composites exhibited characteristic red emission coming from the $\text{}^{5}D_{0} → \text{}^{7}F_{2}$ transition of $Eu^{3+}$ ion in $Gd_{2}O_{3}:Eu^{3+}$. The observed lifetime values, around 1.1 ms, are quite high and suggest successful encapsulation of dopant ions in polymer through gadolinium oxide host. Experimental intensity parameters, transition rates and quantum efficiency of the $\text{}^{5}D_{0}$ emission are calculated from emission spectra using Judd-Ofelt theory. Influence of $Gd_{2}O_{3}:Eu^{3+}$ filler on the modification of glass transition and thermo-degradable properties of the polymer matrix is also investigated. Thermal analyses give evidence of unchanged thermal stability of polymer phase in the composites

Distribution of apparent activation energy counterparts during thermo - And thermo-oxidative degradation of Aronia melanocarpa (black chokeberry)

Kinetics of degradation for Aronia melanocarpa fresh fruits in argon and air atmospheres were investigated. The investigation was based on probability distributions of apparent activation energy of counterparts (ea). Isoconversional analysis results indicated that the degradation process in an inert atmosphere was governed by decomposition reactions of esterified compounds. Also, based on same kinetics approach, it was assumed that in an air atmosphere, the primary compound in degradation pathways could be anthocyanins, which undergo rapid chemical reactions. A new model of reactivity demonstrated that, under inert atmospheres, expectation values for ea occured at levels of statistical probability. These values corresponded to decomposition processes in which polyphenolic compounds might be involved. sa values obeyed laws of binomial distribution. It was established that, for thermo-oxidative degradation, Poisson distribution represented a very successful approximation for sa values where there was additional mechanistic complexity and the binomial distribution was no longer valid. (C) 2017 Elsevier Ltd. All rights reserved

Structural changes in highly crosslinked polyethylene irradiated in absence of oxygen

The heat properties of gamma-ray crosslinked polyethylene are determined by differential scanning calorimetry (DSC). The changes in the supermolecular structure are evaluated and correlated to the heterogeneous distribution of crosslinks in polymer structure caused by the specific early excitation process. The nonlinear change in enthalpy of fusion, peak melting temperature, activation energy of ordering transition, number of defects, and maximal specific heat capacity with absorbed dose is explained in terms of separated crosslinking processes, fast on the lamellae surfaces and slow in the crystal core at double bond site that is evident for absorbed dose greater than 1000 kGy. (C) 2003 Elsevier Science Ltd. All rights reserved.10th Tihany Symposium on Radiation Chemistry, Aug 31-Sep 05, 2002, Sopron, Hungar

TG-DTA-FTIR analysis and isoconversional reaction profiles for thermal and thermo-oxidative degradation processes in black chokeberry (Aroniamelanocarpa)

The thermal and thermo-oxidative processes in Aroniamelanocarpa (black chokeberry) were investigated using combined thermo-analytical (TG-DTA) and spectroscopic (FTIR) experimental techniques. Isoconversional analysis revealed that the process in an inert (argon) atmosphere was probably governed by chlorogenic acid degradation, where autocatalysis (described by the empirical Sestak-Berggren model) might occur due to water already present in the early stages of the process through hydrolysis. Thermal degradation is described by the intrinsic kinetic parameters, where the degradation rate increases proportionally with an increase in the heating rate. Under oxidative conditions, the process was found to be primarily driven by neochlorogenic acid degradation. The thermo-oxidative degradation of Aroniamelanocarpa fresh samples can be described by two competitive reactions, where it was established that a cyanidin-3-glucosylrutinoside degradation made a significant contribution to a comprehensive kinetics. This study showed the targeting of the neochlorogenic acid in Aroniamelanocarpa fresh samples to have a strong hydrogen-donating activity, thereby rendering it capable of very efficiently entrapping the peroxy radicals. Current research has demonstrated that the relative contribution of the two competitive reactions to the overall process is highly dependent on the heating rate of the system under consideration. (C) 2016 Institute of Chemistry, Slovak Academy of Science

A new data in the kinetic and thermodynamic analysis of non-isothermal decomposition of super-fine kaolin powder

Kinetic and thermodynamic analysis of non-isothermal decomposition of super-fine kaolin powder was examined. It was established that the decomposition process proceeds through liberation of adsorbed water, the loss of the water of hydration and dehydroxylation process, which produces highly disordered metakaolin. By applying the distributed reactivity approaches, it was found that dehydroxylation can be described with simultaneous two-parallel reactions model. By applying the Exner-Linert statistical method on estimated Eyring plots, the true isokinetic temperature was confirmed. The appearance of entropy - enthalpy compensation (EEC) showed the direct cause-and-effect relationship between these thermodynamic observables resulting by physically real factors such as the steric factors. It was shown that the phenomenon of true compensation effect arises from conformational (geometrical) changes, which occur during metakaolin formation

Isoconversional kinetic study and accurate determination of lifetime properties for thermal and thermo-oxidative degradation processes of Aronia melanocarpa

Isoconversional analysis and accurate determination of lifetime properties for thermal and thermo-oxidative degradation processes of Aronia melanocarpa were examined. The Sestak-Berggren (SB) autocatalytic model was found as best model to describe degradation process of A. melanocarpa in inert atmosphere. It has been found that autocatalysis may occur from inevitable presence of water probably through the hydrolysis. In the case of thermo-oxidative degradation, it was found that main mechanistic scheme can be presented with two different forms of reaction mechanism function, such as nth-order reaction model (with n GT 1) and SB autocatalytic model. It was determined that neochlorogenic acid represents main compound, which has a strong hydrogen-donating activity. Based on lifetime analysis, it was found that in oxidative conditions, A. melanocarpa shows greater resistance to temperature variations, which correspond to storage conditions and where degradation mechanism greatly affects stability and physico-chemical characteristics of its constituents. Industrial relevance: Current research has a direct industrial application during the testing of responses of blade chokeberry-A. melanocarpa fresh samples on the various thermal stresses in the inert and oxidative reaction conditions. Knowledge of the exact mechanism of degradation (referring to precisely defined reaction pathways) of A. melanocarpa in different reaction atmospheres enables us the targeting an exactly isolated chemical compounds in A. melanocarpa fresh samples, which are responsible for antioxidant protection of human tissue and plasma. The results presented in this paper can be guidelines for the application of industrial processes for precise allocations of these compounds and their further testing for the treatment of malignant diseases. The importance of this research also comes down to the fact that 25% of total polyphenols in chokeberry fruits are anthocyanins, which represent the powerful antioxidants in vitro. Also, the current work provides a specific approach in accurate determination of lifetime properties of A. melanocarpa samples, which is very important in terms of checking the behavior of tested fruit berry system on the temperature variations during storage periods. (C) 2015 Elsevier Ltd. All rights reserved

Application of the Kinetic Triplets and Geometrical Characteristics of Thermal Analysis Curves in Identifying the Main Bioactive Compounds (BC) that Govern the Thermal and Thermo-Oxidative Degradation Mechanism of Aronia melanocarpa (Black Chokeberry)

Thermal and thermo-oxidative kinetics of Aronia melanocarpa fresh samples was investigated. The current investigation was based on the application of kinetic triplets and geometrical characteristics of thermal analysis curves in identifying the main bioactive compounds that govern the thermal and thermo-oxidative degradation mechanisms. From established kinetic model in an argon atmosphere, it was found that released products arise from decomposition of phenolic compounds where autocatalysis may occurs from the inevitable presence of water already in the early stages of the process through the hydrolysis reaction pathway. In the case of thermo-oxidative degradation, it was found that the main mechanistic scheme can be presented with two different forms of reaction mechanism function, such as: nth order reaction model (with n GT 1) (in lower heating mode) and estak-Berggren autocatalytic model (in higher heating mode). Isoconversional analysis has been shown that neochlorogenic acid represents the governed bioactive compound which has a strong hydrogen-donating activity. Based on the mechanistic conclusions, it was established that in an air atmosphere, the cyanidin-3-glucosylrutinoside (Cy-3-GR) degradation significantly participates in overall complex mechanism