Browsing by Author "Avci, A"

Now showing 1 - 20 of 22
  • No Thumbnail Available
    Item
    Syntheses and characterization of poly(iminophenol)s derived from 4-bromobenzaldehyde: Thermal, optical, electrochemical and fluorescent properties
    Kaya, I; Avci, A; Gültekina, Ö
    Schiff base monomers [2-(4-bromobenzylideneamino)phenol and 2-(4-bromobenzylideneamino)-5-methylphenol] were synthesized by the condensation reaction of 4-bromobenzaldehyde with aromatic aminophenols. Then, the monomers were converted to their polyphenol derivatives by oxidative polycondensation reactions (OP) in an aqueous alkaline medium. The structures of the synthesized compounds were characterized by solubility tests, FT-IR, NMR, TG-DTA, DSC and SEC techniques. The HOMO-LUMO energy levels and electrochemical (E (g) ') and optical (E (g) ) band gaps were calculated from cyclic voltammetry (CV) and UV-Vis measurements, respectively. Cyclic voltammetry (CV) was used to determine the electrochemical oxidation-reduction characteristics. Optical properties were investigated by UV-Vis and fluorescence analyses. Solid state electrical conductivities were measured on polymer films by four point probe technique using a Keithley 2400 electrometer. The effects of electron-donating (-CH3) group at p-position of -NH2 group in aminophenol on electrochemical and thermal properties were also discussed. Photoluminescence (PL) properties of the synthesized materials were determined in solution forms using different solvents. Fluorescence measurements were carried out in various concentrated solutions to determine the optimum concentrations to obtain the maximal PL intensities.
  • No Thumbnail Available
    Item
    Synthesis, characterization, and thermal degradation of new aromatic poly(azomethine-urethane)s and their polyphenol derivatives
    Kaya, I; Avci, A
    A new polyurethane was synthesized by condensation reaction of 2,4-dihydroxy benzaldehyde (DHB) with methylene-di-p-phenyl-diisocyanate (MDI) under argon atmosphere. The synthesized polyurethane was converted to its poly (azomethine urethane) species (MP-2AP, MP-3AP, and MP4AP) by graft copolymerization reactions with amino phenols (2-amino phenol, 3-amino phenol, and 4-amino phenol). Obtained poly(azomethine urethane) s (PAMUs) were converted to their polyphenol species (P-MP-2AP, P-MP-3AP, and P-MP-4AP) by oxidative polymerization reaction (OP) using NaOCl as the oxidant. The structures of the obtained compounds were confirmed by FT-IR, UV-vis, H-1-NMR, and C-13-NMR techniques. The molecular weight distribution parameters of the synthesized compounds were determined by the size exclusion chromatography (SEC). The synthesized compounds were also characterized by solubility tests, TGDTA, and DSC analyses. Thermal decomposition steps at various temperatures were clarified by FT-IR analyses of degraded products. Fluorescence measurements were carried out in various concentrated DMF solutions to determine the optimum concentrations to obtain the maximal PL intensities.
  • No Thumbnail Available
    Item
    Photophysical and Thermal Properties of Polyazomethines Containing Various Flexible Units
    Kaya, I; Avci, A; Temizkan, K
    In this study, the poly(azomethine-ether-urethane), poly(azomethine-ester) and poly(azomethine-epoxyether) compounds were prepared to investigate effect of various flexible units on some physical properties like thermal stability and photophysical properties. Structural characterizations were made by FTIR, H-1 NMR, C-13 NMR, and UV-Vis analyses. The molecular weight distributions of polymers were performed by gel permeation chromatography (GPC) measurement. The chemical and physical properties of polymers were examined by thermogravimetry (TG), differential scanning calorimetry (DSC), photoluminescence (PL), dynamic mechanical analysis (DMA), scanning electron microscope (SEM) and atomic force microscopy (AFM) techniques. As a result, the outstanding properties related to the photoluminescence and thermal measurements of the polymers were obtained. Therefore, the presented photoluminescent polymers could be used in thermally stable photo-functional materials.
  • No Thumbnail Available
    Item
    Synthesis, characterization, and thermal stability of novel poly(azomethine-urethane)s and polyphenol derivatives derived from 2,4-dihydroxy benzaldehyde and toluene-2,4-diisocyanate
    Kaya, I; Avci, A
    Up to date, only a few kinds of poly(azomethine-urethane)s (PAMUs) were synthesized and studied with thermal degradation steps. However, polyphenol based PAMUs including azomethine linkages have not been investigated yet. The polyurethanes were prepared by condensation reaction of 2,4-dihydroxybenzaldehyde (2,4-DHBA) with toluene-2,4-diisocyanate (TDI) under argon atmosphere. Synthesized polyurethane was converted to its poly(azomethine urethane) species (TP-2AP, TP-3AP, and TP-4AP) by graft copolymerization reactions with amino phenols (2-amino phenol, 3-amino phenol, and 4-amino phenol). Obtained poly(azomethine urethane)s were converted to their polyphenol species (P-TP-2AP, P-TP-3AP, and P-TP-4AP) by oxidative polymerization reaction (OP) using NaOCl as the oxidant. The structures of the obtained compounds were confirmed by FT-IR. UV-vis, H-1 NMR, and C-13 NMR techniques. The molecular weight distribution parameters of the synthesized compounds were determined by the size exclusion chromatography (SEC). The synthesized compounds were also characterized by solubility tests, TG-DTA, and DSC. Fluorescence measurements were carried out in various concentrated DMF solutions to determine the optimum concentrations to obtain the maximal PL intensities. (C) 2012 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Synthesis, Characterization and Conductivity Properties of Novel Oligomer Schiff Bases Derived from 4-Amino-3-hydrazino-5-mercapto-1, 2, 4-triazole and Their Reactions with VO(IV), Cu(II) Ions
    Kaya, I; Erçag, A; Avci, A; Çulhaoglu, S
    A new Schiff base, 4-(4-hydroxysalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (4HSAHMT), and novel Schiff base oligomers of 4-salicylidenamino-3-hydrazino-5-mercapto-1,2,4-triazole (SAHMT), 4-(2-hydroxynaphthylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (2HNAHMT), 4-(4-hydroxysalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (4HSAHMT) and 4-(5-bromosalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole (BrSAHMT) were synthesized via oxidative polymerization using NaOCl as the oxidant. The structures of the oligomers were supported by FT-IR, UV-Vis, H-1-NMR, and C-13-NMR techniques. The compounds were further characterized by solubility tests, TG-DTA, and elemental analysis. The molecular weight distribution parameters of the compounds were determined by the size exclusion chromatography (SEC). According to SEC, the number average molecular weight (M (n) ) values of O-SAHMT, O-BrSAHMT, O-4HSAHMT and O-2HNAHMT were 2,700, 2,100, 2,700 and 1,000 g mol(-1), respectively. The weight losses of O-SAHMT, O-BrSAHMT, O-4HSAHMT and O-2HNAHMT were 73, 76, 80 and 54 %, respectively, at 1,000 A degrees C. TG analyses showed that the synthesized oligomers were stable toward thermal decomposition. The synthesized oligomers were converted to metal complexes with salts of VO(IV) and Cu(II). The doped and undoped electrical properties of oligomers and oligomer-metal complexes were determined by the four-point probe technique at room temperature and atmospheric pressure.
  • No Thumbnail Available
    Item
    Synthesis of Novel crosslinked Poly(azomethine-urethane)s: Photophysical and thermal properties
    Avci, A; Kamaci, M; Kaya, I; Yildirim, M
    This paper describes synthesis, photophysical, electrochemical and thermal properties of some new flexible crosslinked poly(azomethine-urethane)s. Synthesis procedure includes two main steps: The first one is the synthesis of a polyurethane prepolymer (TP) using toluene-2,4-diisocyanate and 2,4-dihydroxy benzaldehyde, and the second step is the synthesis of resulting flexible crosslinked poly(azomethineurethane) derivatives by conventional polycondensation reaction of TP with different aliphatic diamines. Diamines with various chain lengths (6-12 methylene numbers) were used to obtain various resulting polymers with different physical properties. Photophysical properties of the flexible crosslinked poly(azomethine-urethane)s were investigated using photoluminescence (PL). PL results showed that the flexible crosslinked poly(azomethine-urethane)s exhibited multicolor emission behavior. A linear relationship was observed between the excitation energies and the obtained emission maxima. This characteristic enabled adjusting the PL color at the desired scale. Thermal and morphological properties of the polymers were also investigated using TG-DTA, DSC and AFM techniques. (C) 2015 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Interpretation of acid-base metabolism on arterial blood gas samples via machine learning algorithms
    Ozdemir, H; Sasmaz, MI; Guven, R; Avci, A
    Background Arterial blood gas evaluation is crucial for critically ill patients, as it provides essential information about acid-base metabolism and respiratory balance, but evaluation can be complex and time-consuming. Artificial intelligence can perform tasks that require human intelligence, and it is revolutionizing healthcare through technological advancements. Aim This study aims to assess arterial blood gas evaluation using artificial intelligence algorithms. Methods The study included 21.541 retrospective arterial blood gas samples, categorized into 15 different classes by experts for evaluating acid-base metabolism status. Six machine learning algorithms were utilized; accuracy, balanced accuracy, sensitivity, specificity, precision, and F1 values of the models were determined; and ROC curves were drawn to assess areas under the curve for each class. Evaluation of which sample was estimated in which class was conducted using the confusion matrices of the models. Results The bagging classifier (BC) model achieved the highest balanced accuracy with 99.24%, whereas the XGBoost model reached the highest accuracy with 99.66%. The BC model shows 100% sensitivity for nine classes and 100% specificity for 10 classes, and the model correctly predicted 6438 of 6463 test samples and achieved an accuracy of 99.61%, with an area under the curve > 0.9 in all classes on a class basis. Conclusion The machine learning models developed exhibited remarkable accuracy, sensitivity, and specificity in predicting the status of acid-base metabolism. However, implementing these models can aid clinicians, freeing up their time for more intricate tasks.
  • No Thumbnail Available
    Item
    New Poly(azomethine-urethane)s Including Melamine Derivatives in the Main Chain: Synthesis and Thermal Characterization
    Kaya, I; Yildirim, M; Kamaci, M; Avci, A
    Up to date, only a few kinds of poly (azomethine-urethane)s (PAMUs) derived from aromatic hydroxy compounds were obtained and studied with thermal degradation steps. Novel PAMUs were prepared using the hydroxy-functionalized Schiff bases derived from melamine and toluene-2,4-diisocyanate. Schiff base prepolymers were synthesized by the condensation reaction of melamine with 4-hydroxybenzaldehyde and 2hydroxy-1-naphtaldehyde. Characterization was made by UV-Vis, FTIR, NMR, and SEC techniques. Thermal characterizations of the novel PAMUs were carried out by TG-DTA and DSC techniques. Thermal decomposition steps at various temperatures were also clarified and the physical changes of the synthesized PAMUs with exposing to the thermal degradation steps were displayed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 3027-3035, 2011
  • No Thumbnail Available
    Item
    Synthesis and thermal characterization of novel poly(azomethine-urethane)s derived from azomethine containing phenol and polyphenol species
    Kaya, I; Yildirim, M; Avci, A; Kamaci, M
    Oligophenol-based poly(azomethine-urethane)s (PAMUs) were newly synthesized in two steps. At the first step, the prepolymers including the phenol and oligophenol based-Schiff bases were prepared by a condensation reaction of o-dianisidine with 4-hydroxybenzaldehyde/3-ethoxy-4-hydroxybenzaldehyde, and the polycondensation reactions of the corresponding Schiff bases in an aqueous alkaline media. At the second step, the PAMUs were obtained by copolymerization of the prepolymers with toluene-2,4-diisocyanate (TDI) under an argon atmosphere. The structures of the obtained compounds were confirmed by FTIR, UV-vis, H-1 NMR, and C-13 NMR, and size exclusion chromatography (SEC) techniques. The synthesized compounds were also characterized by TG-DTA and DSC analyses. Thermal decomposition steps at various temperatures were clarified by FTIR analyses of the degraded products. The physical changes to the synthesized PAMUs after exposing them to the thermal degradation steps are displayed.
  • No Thumbnail Available
    Item
    Improved mechanical performance of three-dimensional woven glass/epoxy spacer composites with carbon nanotubes
    Yildirim, F; Aydin, M; Avci, A
    Three-dimensional polymer composites offer various features and design options due to their hollow structure and lightweight. However, to exploit their advantages, it is a must to improve their structural features and mechanical performances including out-plane direction. Although introducing thermoplastic fillers between the plies or multilayered design addresses on this critical issue, the benefits offered by the nanoparticles with superior mechanical properties come a step forward as an another engineering solution. Based on this motivation, the goal of this study is to investigate the impact of multiwalled carbon nanotubes on the mechanical and thermomechanical performances of three-dimensional woven glass/epoxy spacer composites. Therefore, multiwalled carbon nanotubes at various content were introduced into epoxy matrix, and the multiwalled carbon nanotubes-epoxy mixture was infused to three-dimensional woven fabric with the vacuum-assisted resin transfer method. The obtained results indicated that the three-point bending strength and modulus were enhanced up to 25 and 80% for warp direction and enhanced up to 44 and 85% for weft direction with carbon nanotube addition, respectively. Tensile strength developed in the warp direction by 7%, while the strength value in the weft direction did not change. The tensile strain values for warp and weft directions enhanced up to 19 and 12% with carbon nanotube addition, respectively. In addition, thermomechanical analysis has revealed that the glass transition temperature and storage modulus were also improved. Particle dispersion detection with color measurement and scanning electron microscopy analyses revealed the effectiveness of the ultrasonic mixing on the dispersion of carbon nanotubes in the epoxy matrix. The consequences of carbon nanotube addition on microscale morphology were discussed based on the fracture morphologies to nanoscale and microscale toughening mechanisms in the existence of carbon nanotube reinforcement.
  • No Thumbnail Available
    Item
    The crosslinked poly(azomethine-urethane)s containing o-hydroxyazomethine: Tunable multicolor emission, photophysical and thermal properties
    Kamaci, M; Avci, A; Kaya, I
    This article presents synthesis, photophysical, electrochemical, thermal, and morphological properties of the crosslinked polyurethanes (CLPUs). CLPUs were synthesized in two main steps. In the first step, aldehyde functionalized polyurethane prepolymer was synthesized using 2,4-dihydroxy benzaldehyde and hexamethylene diisocyanates. In the second step, the prepared prepolymer was converted to the crosslinked polyurethane derivatives using different diamines via condensation reaction. Diamines with various chain length and side-group substitutions were used as crosslinker. Photophysical properties of the crosslinked polyurethanes were investigated using UV-vis and photoluminescence (PL) spectra techniques. Fluorescence measurements showed that CLPUs exhibited multicolor emission behavior. Additionally, a linear relationship is determined between the excitation energies and the obtained emission maxima and, this property allows tuning the PL color by changing the source light energy on the desired scale. (C) 2015 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Improving the Mechanical, Physical, Thermal, and Morphological Properties of Isotactic Polypropylene with Dialkylperoxide
    Sirin, K; Yavuz, M; Çanli, M; Avci, A; Dogan, F
    In this study, the influence of the visbreaking agent (DAP) on mechanical, physical, thermal and morphological properties of PP has been studied. For this reason, isotactic polypropylene (PP) matrices containing 0.01, 0.02, 0.04, 0.06, 0.08, and 0.1 wt% of dialkylperoxide [2, 5-dimethyl-2, 5-di (tert-butyl peroxy)-hexane, (DAP)] were prepared by using a single-screw extruder. As a result of DAP addition, the crystallinity ratio of the PP matrices has changed between 2.67-7.80%. Mechanical properties of the matrices have been improved. Particularly, the mechanical tests of PP have given interesting results when compounded with 0.02 wt.% dialkyl peroxide. The microstructure of isotactic polypropylene matrix was investigated by scanning electron microscopy (SEM). From SEM analysis, it was observed that the surface disorder increased by the increasing amount of DAP. Thermal analyses of the matrices were investigated using thermogravimetry in dynamic nitrogen atmosphere at different heating rates. The Flynn-Wall-Ozawa (FWO), Kissinger and master plots method were employed to determine the kinetic model and kinetic parameters of the decomposition processes under non-isothermal conditions. It was found that the thermal stability, activation energy and thermal decomposition processes were all changed by increasing amount of DAP in the matrix structure.
  • No Thumbnail Available
    Item
    Fluorescence, thermal and electrochemical properties of poly(azomethine-urethane)s containing sulfone group
    Avci, A; Temizkan, K; Kaya, I
    In this study, the new sulfone group-containing poly(azomethine-urethane)s (PAZUs) were synthesized to investigate the effects various diisocyanates on the thermal, fluorescence, electrochemical and morphological properties. The structures of PAZUs have been confirmed by FT-IR, NMR, and SEC analyses. The electrochemical behaviors of the PAZUs were examined by cyclic voltammetry. Optical properties were investigated by UV-Vis and fluorescence measurements. The PAZUs were further characterized by TGA, DSC, SEM, and AFM techniques. TGA analyses results showed considerable increase in the thermal stability of polyurethanes due to the introduction of azomethine bond in the main chain. Consequently, because of the fine thermal properties the obtained materials can be used to produce thermally stable materials.
  • No Thumbnail Available
    Item
  • No Thumbnail Available
    Item
    Fluorescence, Thermal, Electrochemical, and Morphological Properties of New Poly( Urethane-.Imide)s: Synthesis and Characterization
    Avci, A; Sirin, K
    New thermally stable poly(urethane-imide)s (PUIs) were synthesized to investigate aliphatic and aromatic group effects on various properties such as thermal stability and electrochemical properties. Thermal characterizations were carried out by TG-DTA and DSC techniques. TGA results showed that the PUIs derived from aromatic diisocyanates had relatively higher thermal stabilities as compared to the aliphatic diisocyanate. They have between 223-245 degrees C onset temperature and above 37% char at 1000 degrees C. Also, thermal degradation values show that PUIs have higher stability than conventional PU. DSC results showed that the new PUIs have Tg values between 134 and 138 degrees C. Fluorescence measurements were performed using dimethyl sulfoxide solutions and also, the optimization of the concentrations maximal emission intensity was investigated in dimethyl sulfoxide. As a result, the remarkable properties related to the fluorescence and thermal measurements of the polymers were obtained. Therefore, these polymers could be used in various application fields because of the fluorescent and thermal properties.
  • No Thumbnail Available
    Item
    Thermal, fluorescence, and electrochemical characteristics of novel poly(urethane-imide)s
    Avci, A; Sirin, K
    In this study, the novel thermally stable poly(urethane-imide)s (PUIs) were synthesized. The structures of the obtained polymers were confirmed by FT-IR and NMR techniques. The molecular weight distribution parameters of the synthesized PUIs were determined by the size exclusion chromatography (SEC). The synthesized PUIs were also characterized by solubility tests, solution viscosity, TG-DTA, and DSC analyses. Cyclic voltammetry measurements were carried out, and HOMO-LUMO energy levels and electrochemical band gaps were calculated from their absorption edges. Additionally, optical band gaps (E-g) were determined by using UV-vis spectra of the materials. Fluorescence measurements were carried out in various concentrated DMSO solutions to determine the optimum concentrations to obtain the maximal PL intensities. Also, morphological characterizations were made by scanning electron microscopy technique.
  • No Thumbnail Available
    Item
    Impact response of nanoparticle reinforced 3D woven spacer/epoxy composites at cryogenic temperatures
    Yildirim, F; Tatar, AC; Eskizeybek, V; Avci, A; Aydin, M
    Fiber-reinforced polymer composites serving in harsh conditions must maintain their performance during their entire service. The cryogenic impact is one of the most unpredictable loading types, leading to catastrophic failures of composite structures. This study aims to examine the low-velocity impact (LVI) performance of 3D woven spacer glass-epoxy composite experimentally under cryogenic temperatures. LVI tests were conducted under various temperatures ranging from room temperature (RT) to -196 degrees C. Experimental results reveal that the 3D composites gradually absorbed higher impact energies with decreasing temperature. Besides, the effect of multi-walled carbon nanotube and SiO2 nanofiller reinforcements of the matrix on the impact performance and the damage characteristics were further assessed. Nanofiller modification enhanced the impact resistance up to 30%, especially at RT. However, the nanofiller efficiency declined with decreasing temperature. The apparent damages were visually examined by scanning electron microscopy to address the damage formation. Significant outcomes have been achieved with the nanofiller modification regarding the new usage areas of 3D woven composites.
  • No Thumbnail Available
    Item
    A new selective fluorescent sensor for Zn(II) ions based on poly(azomethine-urethane)
    Avci, A; Kaya, I
    A new and selective fluorescent sensor based on poly(azomethine-urethane) (PAMU) is synthesized and characterized by FT-IR, H-1 NMR, and size exclusion chromatography (SEC) techniques. The new sensor shows a high selectivity for Zn(II) over other metal cations in DMF/deionized H2O (1:2, v/v). The fluorescence sensor gives a linearly and highly stable response to Zn(II) as an increasing emission peak at 595 nm. The sensitivity limit of the new sensor is found to be 11.4 x 10(-3) mol L-1. The results show that the proposed sensor can be efficiently used as a simple method for the detection of Zn(II) ions. (C) 2015 Elsevier Ltd. All rights reserved.
  • No Thumbnail Available
    Item
    Synthesis of thermally stable and low band gap poly(azomethine-urethane)s containing fluorene unit in the backbone
    Kaya, I; Avci, A; Temizkan, K
    New poly(azomethine-urethane)s (PAMU)s were prepared to investigate the effects of different four diisocyanates on some physical properties such as thermal stability, optical and electrochemical properties. First, the fluorene Schiff base was synthesized as in the literature. Then, this Schiff base was converted to poly(azomethine-urethane)s using diisocyanates (2,4-toluenediisocyanate, 1,4-phenylene diisocyanate, methylene-di-p-phenyl-diisocyanate, and hexamethylene-diisocyanate) via condensation reaction. Second, the structures of PAMUs were confirmed by FT-IR, NMR, and UV-Vis spectral analyses. Cyclic voltammetry (CV) was used to determine the electrochemical oxidationreduction characteristics of (PAMU)s. The CV results of PAMUs compounds showed to have an electrochemical band gap below such as 2.0 eV. The PAMUs were characterized by TGA, DSC, SEM, SEC and AFM techniques. TGA analysis results of compounds showed considerable increasing of the thermal stability of polymers, because of finding of azomethine bond in the main chain.
  • No Thumbnail Available
    Item