Radiation, thermal and optical properties of PVA films containing arylazo pyridone dyes

Films based on polyvinyl alcohol (PVA) containing different concentrations of some arylazo pyridone dyes have been introduced as plastic detectors for dosimetry. PVA was chosen due to its water solubility and the possibility to incorporate a variety of dyes. The significance of arylazo pyridone dyes resides in their simple synthesis and wide application areas. The following dyes were used in optical data storage, laser technology, dye-sensitized solar cells, non-linear optics and biological systems. The advantage of polymeric films based on arylazo pyridone dyes is a visual change of color after exposure to gamma radiation, making them easy to use. In addition, this form of dosimeters is cheap and easily portable. Films containing arylazo pyridone dyes change the color when irradiated with γ-radiation at least up to 20 kGy. The color changes were confirmed spectrophotometrically. All synthesized films were characterized by FTIR. Optical properties have been analyzed on the basis of reflection and excitation spectra. Thermal degradation processes of PVA films containing arylazo dyes were investigated with thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC).VII International Conference on Radiation in Various Fields of Research : RAD 2019 : book of abstracts; June 10-14, 2019; Herceg Novi, Montenegr

A comparative study of photocatalytically active nanocrystalline tetragonal T zyrcon- type and monoclinic scheelite-type bismuth vanadate

The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ). The work of K. Smits was supported by Latvian National Research Program IMIS2 (Grant no. 302/2012 ).Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Routing of optical beams by asymmetric defects in (non)linear waveguide arrays

Uniform one-dimensional (1D) nonlinear waveguide array, consisting of parallel, evanescently coupled waveguides represent a special case of 1D photonic crystal [1]. Matured fabrication procedures enable production of arrays whose intrinsic parameters (such as shape and dimensions of the waveguides, coupling strength between them, nonlinear response,…) may be easily changed. The possibility to manipulate light propagation through photonic crystals in a fully controllable fashion, have promise in the field of all-optical communications and photonic devices. However, unavoidable material imperfections, together with slight deviation during fabrication and misusage lead to existence of random defects in the system, which considerably hamper the control of the light flow. These imperfections enable the existence of different types of stable, localized defect modes (breathers and solitons [2]) which may be useful in routing, blocking and filtering of light. Interestingly, various defects may be intentionally inserted in uniform waveguide arrays, enabling studies of defect modes and their influence on light dynamics [3-5]. Interface of two semi-infinite waveguide arrays represent a type of structural (geometric) defect which also can host different localized modes [6, 7]. Recently, the influence of two nonlinear defects on light propagation through linear waveguide array [8] and the steering of discrete breathers in a linear lattice with two nonlinear defects [9] have been explored. Finally, light trapping, reflection and transmission near defect modes in composite linear photonic lattices have been investigated [10]. Here, we studied numerically (by split-step Fourier method) light beam propagation through either uniform of composite 1D (non)linear waveguide arrays having two asymmetric defects, a situation which can be fairly well modeled by the paraxial time-independent Helmholtz equation. Embedded asymmetric defects are either linear or nonlinear. Effects of different positions and widths of asymmetric defects on the light beam propagation have been examined and compared with a case of embedded symmetric defects. Various types of modes localized at these defects and in their vicinity have been found. We also have explored influence of asymmetric defects on tilted beam propagation and identify regimes of trapping, total reflection and transmission of light. Presented results provide an insight into the light beam dynamics in the presence of asymmetrical linear and nonlinear defects and might be useful in several all-optical applications such as filtering and steering of light beams through the optical medium.VI International School and Conference on Photonics and COST actions: MP1406 and MP1402 : PHOTONICA2017 : August 23 - September 1, 2017; Belgrade

Hydrolytic, thermal, and UV stability of urea‐formaldehyde resin/thermally activated montmorillonite nanocomposites

Urea-formaldehyde resin (F/U ratio of 0.8)/thermally activated montmorillonite (UF/Delta TK10) nanocomposite was synthesized. The hydrolytical, thermal, and UV radiation stability of UF/Delta TK10 nanocomposites are determined. UF hybrid nanocomposites have been irradiated with UV light with a wavelength of 254 nm and 366 nm, and after that, their radiation stability was evaluated. The free formaldehyde (FA) percentage in all prepared samples was determined. The sample was characterized by using X-ray diffraction analysis (XRD), nonisothermal thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential thermal gravimetry (DTG), with infrared (FTIR) spectroscopy. Crosslinked UF/Delta TK10 nanocomposite shows the highest resistance to acid hydrolysis after UV irradiation at a wavelength of 254 nm. The values for T-5% are identical for the unirradiated and UV irradiated (wavelength of 366 nm) UF/Delta TK10 nanocomposite. It can be concluded that this sample is thermally most stable and shows good resistance to UV irradiation

Synthesis and thermal properties of arylazo pyridone dyes

Thermal degradation properties of 5-(4-substitutedphenylazo)-3-amido-6-hydroxy-4-methyl-2-pyridones and 5-(4-substitutedphenylazo)-3-cyano-6-hydroxy-4-methyl-2-pyridones dyes, differing in electron withdrawing and electron donating substituents in para-position of diazo components were examined. The structure of the synthesized compounds has been confirmed by 1H NMR,13C NMR, FTIR, UV–Vis and XRD analysis techniques. The results obtained with thermogravimetric analysis (TGA) – derivative thermogravimetry (DTG) and differential thermal analysis (DTA) were combined with GC-mass spectral fragmentation to obtain thermal decomposition mechanism. Non-isothermal kinetics were monitored by application of TGA-DTG-DTA. For Kinetic behavior of the investigated dyes during their degradation in an inert atmosphere, Kissinger, Ozawa, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) isoconversional (model-free) methods were applied. It was found that different thermal stabilities of investigated dyes are the consequence of their different chemical structures, including diverse substituents. © 201