Browsing by Author "Evingur, Gulsen Akin"

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Citation Count: 0
The Effect of Pyranine and MoS₂ Content on the Optical Properties of Polyacrylamide-MoS₂ Composite Gels
(Taylor & Francis inc, 2024) Uysal, Bengu Ozugur; Osma, Busra; Evingur, Gulsen Akin; Pekcan, Onder
The most favorable members of the class of two-dimensional (2D) materials, molybdenum sulfide (MoS2), graphene, and tungsten disulfide (WS2) have become a thriving research frontier for many applications, ranging from catalysis to optoelectronic devices, due to their superior electronic behavior and mechanical properties. Making a new, smart, hydrogel when incorporating MoS2 into basic hydrogels can change their optical, electronic, and mechanical properties. In this work, MoS2-doped polyacrylamide (PAAm) gels were prepared via the free radical crosslinking copolymerization technique at room temperature without pyranine which is often used for crosslinking PAAm. The optical properties of PAAm-MoS2 composite gels were investigated, and they were analyzed using ultraviolet (UV) and fluorescence spectroscopy. The absorbance was measured before and after diffusion of MoS2-doped PAAm, and after the release of pyranine in and out of the composite gel, respectively. The shift of the absorption edge toward shorter wavelengths was seen when the quantity of MoS2 in the PAAm composite gels was decreased. The constituents included in the polymer composites exhibited notable photon energy absorption within the visible and ultraviolet spectra. This absorption phenomenon induced electron transitions to states of elevated energy. Parameters, such as refractive index and extinction coefficient, were analyzed with respect to the content of MoS2. When the MoS2 amount was increased in the gels, the percentage of reflectance increased. The extinction coefficient increased at longer wavelength and it decreased in the UV range, the shorter wavelength region. The results suggested that MoS2-doped PAAm composite gels show promising optoelectronic properties for developing optoelectronic devices.
Citation Count: 1
Optical and mechanical properties of PNIPAm-MWCNTs and PNIPAm-GO composites
(Wiley, 2023) Unver, Batuhan; Pekcan, Onder; Evingur, Gulsen Akin
The aim of this study is to investigate drying, swelling, elastic properties, and to produce optical band gap energies on the performance of Poly (N-Isopropyl acrylamide) - Multi walled carbon nanotubes (PNIPAm - MWCNTs) and Poly (N-Isopropyl acrylamide)- Graphene Oxide (PNIPAm-GO) composites, respectively. The composites were prepared by free radical crosslinking copolymerization. Drying and swelling of PNIPAm-MWCNTs and PNIPAm- GO composites were performed by using steady state fluorescence technique. Firstly, the desorption coefficients of the composites were modeled by using Fick's Law. Cooperative diffusion coefficients were calculated by employing Li-Tanaka Model. When composite doped with 10 wt% of MWCNTs has a higher desorption coefficient than composite doped with the same amount of GO, 40wt% of GO content in the PNIPAm has a higher diffusion coefficient than the composite that has 40wt% of MWCNTs content in the swelling process. Secondly, the composite that has 40wt% of MWCNTs content has a higher modulus before swelling than the composite that has the same amount of GO contents. Lastly, optical band gap energies were calculated by using Tauc's approach, and Urbach's relation by using the data performed UV Spectroscopy. We found that PNIPAm -GO has a much narrower band gap value.
Citation Count: 3
Optical, Mechanical, and Electrical Properties of Polymer Composites Doped by Multiwalled Carbon Nanotubes
(Intechopen, 2016) Evingur, Gulsen Akin; Pekcan, Onder
Three-dimensional networks can be hydrophilic and/or hygroscopic. Optical, mechanical, and electrical properties of these materials encompass many fields of technology. Composites of carbon nanotubes (CNTs) in polymeric materials have attracted considerable attention in the research and industrial communities due to their unique optical, mechanical, and electrical properties. CNT polymer nanocomposites possess high stiffness, high strength, and good electrical conductivity at relatively low concentrations of CNT filler. Here, in this chapter, we survey the optical, mechanical, and electrical mechanisms for various polymeric systems. Composite gels and films were prepared with various molar percentages of multiwalled carbon nanotubes (MWCNTs). The optical, mechanical, and electrical behaviors of various composite gels doped by MWCNT are also discussed in the each sections of the chapter. The optical behaviors of the composites were performed by the UV-Vis spectroscopy and fluorescence spectroscopy in the first part of the chapter. On the other hand, compressive testing technique and rheological measurements were employed to determine the variations of mechanical properties of the composites in the second part of the chapter. Lastly, we review the electrical properties of the composites improved significantly by addition of MWCNTs researches.
Citation Count: 3
Polyacrylamide mediated polyvinyl pyrrolidone composites incorporated with aligned molybdenum disulfide
(Wiley, 2022) Uysal, Bengu Ozugur; Evingur, Gulsen Akin; Pekcan, Onder
In this study, we aimed to design a mechanically durable material consisting of Molybdenum disulfide (MoS2) as 2D material and polyvinyl pyrrolidone (PVP) enhanced Polyacrylamide (PAAm) composites. Composites containing different amounts of MoS2 were synthesized via a free-radical crosslinking copolymerization method. They were characterized using UV-visible spectroscopy, fluorescence, and mechanical techniques to illuminate band gap energy, absorption, slow release kinetics, and modulus of the composites. Furthermore, the effect of swelling on the elasticity of the composites was investigated. It was observed that the elasticity exhibited similar band gap energies with respect to the MoS2 content. The results demonstrated that the MoS2 content strongly influences the optical and mechanical properties of the composites and consequently physical parameters of the composites have been correlated with the various amounts of MoS2.
Citation Count: 0
A Quartz Crystal Microbalance (QCM) Study on the Formation of Aqueous ?-Carrageenan-Chitosan Composite Bilayers with NaCl and Graphene Oxide
(Taylor & Francis Inc, 2023) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, Onder; Evingur, Gulsen Akin
Biomaterials and thin biofilms play a fundamental role in the medical, food and pharmaceutical industries. The Quartz crystal microbalance (QCM) measurement technique is one of the attractive techniques which have been used for monitoring the thin-film formation process. In the current work described here, kappa-carrageenan and chitosan solutions were used for the layer-by-layer (LBL) deposition of polyelectrolyte multilayers (PEMs) on the gold surface of a 5 MHz AT-cut (thickness-shear mode) quartz crystal in a flow module. A sensitive QCM system was designed to detect 0.1 Hz differences in the resonance frequency (Delta f) and 10(-7) changes in the energy dissipation (Delta D) values, which are the measures of the deposited mass and the film rigidity, respectively. Negatively charged carrageenan and positively charged chitosan biomolecules in the solutions were used to build up sequential and very thin bilayers on the modified gold surface. The effects of NaCl and graphene oxide (GO) addition on the mass of the deposited films were also investigated. Intermolecular interactions between the biopolymer chains, Na+ cations and GO sheets were explained by interactions between molecules, such as electrostatic forces and hydrogen bondings.