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Öğe 4-(Benzimidazolisonitrosoacetyl)biphenyl modified chitosan and its copper complex: Synthesis and electrorheological properties(Elsevier Sci Ltd, 2025) Kayapa, Faruk; Karipcin, Fatma; Ozen, Muruvvet Begum; Gumus, Omer Yunus; Unal, Halil IbrahimA novel chitosan Schiff base derivative (CsB) was synthesized for the first time by a condensation reaction of chitosan with 4-(benzimidazolisonitrosoacetyl)biphenyl. As a result of the coordination reaction of copper ions, its copper(II) complex (CsBCu) was constructed. Then, the structures were confirmed by ICP-OES, ATR-FTIR, TG/ DTA, and SEM analysis. Furthermore, electrorheological (ER) properties of the synthesized compounds, as a new dry-based ER fluid, were extensively studied in silicone oil (SO). CsBCu/SO exhibited a higher shear stress value of 78 Pa at a 2.5 kV mm-1 applied electrical field than Cs/SO and CsB/SO, which is attributed to the contribution of the paramagnetic nature of the Cu element. The shear and oscillation tests revealed ER and viscoelastic behavior of the suspensions upon applying an external electric field (E).Öğe A comparative study of coal fly and bottom ashes as sustainable electroactive vibration damping materials(Korean Soc Environmental Engineers - Ksee, 2024) Begen, Deniz; Calis-Ismetoglu, Gokce; Gumus, Omer Yunus; Unal, Halil IbrahimCoal is used in most of the power and chemical plants to meet energy needs which produce various waste ashes. Reuse of these ashes as electroactive materials has great importance for sustainable development. In this study, it was detected that the main components of coal fly (CFA) and bottom ashes (CBA) were oxides of silica (SiO2), 2 ), iron (Fe2O3), 2 O 3 ), aluminium (Al2O3), 2 O 3 ), and magnesium (MgO), besides carbon. These are well-known electrorheological (ER) active materials. The aim of this study is to reveal dielectric and electroactive vibration damping capabilities of CFA and CBA. According to the dielectric and ER flow tests carried out in insulating silicone oil (SO), the optimum concentration of particles was determined to be 35 wt.% for both ashes. Higher ER yield stress (tau y tau y = 135 Pa), higher ER efficiency (32.8), and better viscoelastic properties (tau c= tau c = 128 Pa, G' = 680 kPa) under 3.0 kV mm-1 applied electric field were obtained for 35CFA/SO suspension system compared to 35CBA/SO (tau y tau y = 125 Pa, ER eff = 24.0, tau c = 55 Pa, G' = 260 kPa). Although it was concluded that both ashes can be upcycled to sustainable and smart vibration damping alternative materials, better performance was observed for CFA particles.Öğe Effect of surfactant on the dielectric and electrorheological properties of zinc borate/silicone oil dispersions(Springer, 2019) Gümüş, Ömer Yunus; Unal, Halil IbrahimZinc borate (ZB) particles dispersed in silicone oil (SO) at concentrations of phi = 5vol%-20vol% were subjected to dielectric analysis to elucidate their polarization strength, time, and mechanism. Results revealed that all virgin dispersions lacked polarization. Triton X-100, a non-ionic surfactant, was added to ZB/SO dispersions to enhance the polarizability of ZB particles. The addition of 1vol% Triton X-100 enhanced the polarizability of ZB/SO dispersions, and the 15vol%ZB/SO system provided the highest dielectric difference Delta epsilon ' (the difference in epsilon ' values at zero and infinite frequency, Delta epsilon ' = epsilon(0) - epsilon(221D)) of 3.64. The electrorheological (ER) activities of the ZB/SO/Triton-X dispersion system were determined through the ER response test, and viscoelastic behaviors were investigated via oscillation tests. A recoverable deformation of 36% under an applied electrical field strength of 1.5 kV/mm was detected through creep and creep recovery tests.Öğe Electroactively smart vibration damping suspensions of diatomite/silicone oil(Springer, 2022) Ozdemir, Ceren; Gumus, Omer Yunus; Calis-Ismetoglu, Gokce; Unal, Halil IbrahimIn this study, the literature gap for diatomite/silicone oil (SO) suspensions is fully investigated. Firstly, the structure, size, zeta-potential, morphology, thermal, and conductivity properties of diatomite are searched. Then, dielectric properties of a series of diatomite/SO suspensions with various volumes are analyzed and the effects of concentration on dielectric properties are discussed based on the interparticle distances. Optimum 10 volume% diatomite/SO suspensions are observed to show shear thinning behavior with yield stresses of 0.6 +/- 1.8 Pa and 47 +/- 5.2 Pa at E=0 kV/mm and E=3.5 kV/mm, respectively. The viscoelastic test shows that the suspension has vibration damping capability under both off and on-electric fields owing to the dominant elastic behavior. According to the creep-recovery results, the suspension system exhibits 25% recovery under E=3.5 kV/mm. This indicates that the diatomite/SO suspension system can be used as an electroactive vibration damping material.Öğe One-Pot Preparation of Electroactive Shape Memory Polyurethane/Carbon Black Blend(Springer, 2021) Uranbey, Leyla; Unal, Halil Ibrahim; Calis, Gokce; Gümüş, Ömer Yunus; Katmer, Sukran; Karatas, CetinShape memory polymers are the materials that can recover their original shape after a large deformation when exposed to an external stimulus such as electric field, pH, temperature, light, magnetism or humidity. With these properties, it is possible to use them in many areas in the industry. In this study, a shape-memory polymer compound was developed which is capable of changing its shape when subjected to an external voltage. Electroactive shape memory polymer compound was prepared by mixing commercially available and economically viable thermoplastic shape memory polyurethane (SMPU) with carbon black (CB), which has low cost and high electrical conductivity, by adding at various proportions. Conductivity, structural, morphological, homogeneity, thermal, rheological and shape memory characterizations of the SMPU/CB blend were carried out by four-probe measurements, ATR-FTIR spectroscopy, x-ray diffraction analysis, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analyses, melt flow index (MFI), and a thermal camera imaging methods, respectively. The effects of CB loading ratios on these characteristics of SMPU/CB blends were investigated. It was concluded that SMPU/20CB blend can be used as a commercial material having shape memory characteristics.Öğe Synergistic Effects of Surfactant on Dielectric and Electrorheological Properties of Boronic Acid Derivative Polymer Dispersions(Wiley-V C H Verlag Gmbh, 2016) Ozkan, Seyma; Gümüş, Ömer Yunus; Unal, Halil IbrahimElectric field stimulus fluids are prepared by dispersing poly(3-aminophenylboronic acid, PABA) and poly(thiophene-3-boronic acid, PTBA) nanoparticles in silicone oil (SO). Upon addition of a nonionic surfactant, Triton X-100, to the fluids, enhanced polarizabilities are detected on dielectric analysis which is driven by the increased number of dipole centers in their structures. Very high colloidal stability is observed for PABA/SO/Triton-X dispersion system since it has zeta(zeta)-potential value in colloidally stable region, whereas PTBA/SO/Triton-X dispersion system exhibits some degree of sedimentation due to low zeta-potential value. When electric field strengths are applied, increased yield stresses of the dispersions are detected. Storage and loss moduli values of PABA/SO/Triton-X and PTBA/SO/Triton-X dispersions suggest that the suspensions have vibration damping capabilities. Further, reversible non-Newtonian viscoelastic deformations are observed from the creep-recovery tests of the systems and they are classified as smart materials. Furthermore, the results show that PABA based colloidal system has better dielectric and rheological properties than that of PTBA and these results are also discussed in terms of particle conductivity and molecular structure.
