11 results
Search Results
Now showing 1 - 10 of 11
Review Citation - WoS: 5Binary Alloy Clusters: Structures and Electronic Properties(Amer Scientific Publishers, 2014) Pekoez, Rengin; Oymak, Hueseyin; Erkoc, AkirSynthesis, characterization, physics, and chemistry of nanoclusters have been the focus of intense attention for the last two decades. Also, their unique statues that they are between molecule and bulk material is the central reason for the theoretical researcher to understand the transition from atom to cluster/molecule and then to solid state. In this review we restrict ourselves to the recent advances in the structural and electronic properties of binary alloy clusters. This type of clusters is particularly of importance thanks to their very availability for being tuned, by changing their sizes, according to any special needs. A brief summary of the classification of clusters as well as the experimental techniques and theoretical methods to study them, and the possible applications of alloy clusters are given in the introduction part. Several binary alloy cluster types, including semiconductor, alkali and transition metal, oxide, and ionic binary alloy clusters, are widely reviewed considering extensively the most recent articles.Article Citation - WoS: 6Citation - Scopus: 6Modification of Poly(methyl Methacrylate) Surfaces With Oxygen, Nitrogen and Argon Plasma(Amer Scientific Publishers, 2014) Ozgen, Ozge; Özgen, Özge; Hasirci, Nesrin; Özgen, Özge; Physics Group; Physics GroupPoly(methyl methacrylate) (PMMA) is a strong and lightweight material used in wide range of areas changing from lenses to medical and dental devices. In this study, PMMA samples were modified by oxygen, nitrogen and argon plasma with application of 100 watts 13.56 MHz radio frequency (RF) discharge for different periods (5 min, 15 min and 30 min) and the effects of plasma parameters on surface chemistry, hydrophilicity, surface free energy and topography were examined. XPS analysis showed formation of free carbonyl and carbonate groups by oxygen plasma, carboxylic acid and free carbonyl by argon plasma, and imine, primary amine, amide and nitrozo functional groups by nitrogen plasma treatments. For all cases plasma treatment created more hydrophilic surfaces with lower water contact angles than that of pristine PMMA. Also, plasma caused an increase in the surface free energy and its' polar components determined by Geometric Mean, Harmonic Mean, and Acid-Base approaches. AFM results showed increasing roughness parallel to the duration of plasma. As a result, each plasma treatment caused different functionalities and physical topographies on PMMA surfaces and different functionalities can be used for further developments such as binding specific active molecules to design biosensors or medical devices.Review Citation - WoS: 23Controlled Gene Delivery Systems: Nanomaterials and Chemical Approaches(Amer Scientific Publishers, 2020) Ahmadi, Sepideh; Rabiee, Navid; Fatahi, Yousef; Bagherzadeh, Mojtaba; Gachpazan, Meysam; Baheiraei, Nafiseh; Hamblin, Michael R.Successful gene therapy depends on the design of effective gene delivery systems. A gene delivery system is considered a powerful tool for the release of genetic material within cells resulting in a change in cell functions and protein production. The release of genes in a controlled manner by using appropriate carriers facilitates their release without side effects and increases the expression of genes at the released site. It is expected that significant changes in the combination of several genes and drugs can be provided by developing treatment systems sensitive to different stimuli such as redox potential, pH variations, temperature gradients, light irradiation, and enzyme activity. The most important advantages for the release of genes and stimuli-responsive therapeutics include delivering vectors locally, reducing side effects and causing no toxicity to distant tissues while at the same time reducing the immune response to the vectors. In this review, we aim to discuss different types of gene carriers involved in the controlled transfer of nucleic acids (non-viral inorganic and organic nanoparticles (NPs) and virus-like particles (VLPs)) as well as the simultaneous transfer of several genes and/or drugs into cells or different tissues, providing for an efficient and safe treatment of numerous diseases.Article Effects of Graphene Transfer and Thermal Annealing on Anticorrosive Properties of Stainless Steel(Amer Scientific Publishers, 2017) Oh, Jeong Hyeon; Han, Sangmok; Kim, Tae-Yoon; Park, Jongee; Ozturk, Abdullah; Kim, Soo YoungStainless steel (STS) films were annealed in a thermal quartz tube and covered with graphene to improve their anticorrosive properties. Graphene was synthesized via the chemical vapor deposition method and transferred onto the surface of the STS film by the layer-by-layer approach. The structure of the STS film changed from alpha-Fe to gamma-Fe after annealing at 700 C for 1 h, resulting in an increase of 82.72% in the inhibition efficiency. However, one-layer graphene acted as a conductive pathway and therefore deteriorated the anticorrosive properties of the STS film. To overcome this problem, graphene was transferred layer by layer onto the STS film. It was found that transfer of three layers of graphene onto the STS film resulted in a 91.57% increase in the inhibition efficiency. Therefore, thermal annealing and transfer of multilayer graphene are considered to be effective in enhancing the anticorrosive properties of STS films.Article Citation - WoS: 10Alkaline Hydrothermal Synthesis, Characterization, and Photocatalytic Activity of Tio2 Nanostructures: the Effect of Initial Tio2 Phase(Amer Scientific Publishers, 2019) Erdogan, Nursev; Park, Jongee; Choi, Woohyuk; Kim, Soo Young; Ozturk, AbdullahOne-dimensional (1D) titanate nanostructures were synthesized by hydrothermal route, using commercially available TiO2 (P25) and anatase powders as precursor materials and strong NaOH solution as catalyzer. The prepared titanates were calcined, followed by protonation to produce TiO2 nanostructures having enhanced photocatalytic and photovoltaic properties. The synthesized TiO2 1D nanostructures were characterized using field-emission scanning electron microscope, high-resolution electron microscope, X-ray diffraction analysis, and UV-Vis photospectroscopy to understand the effect of initial TiO2 phase on morphological and crystallographic features, and bandgap. Methylene blue degradation test was applied to evaluate the photoactivity of the products obtained after different stages of the process. The findings indicate that 1D TiO2 nanostructures form by different mechanisms from dissolved aggregates during hydrothermal process, depending on the crystal structure of the initial precursor used. Photocatalytic test results reveal that protonated titanates have considerable adsorption capability, while photocatalytic degradation depends on TiO2 transformation.Article Citation - WoS: 11Development of Antibacterial Composite Electrospun Chitosan-Coated Polypropylene Materials(Amer Scientific Publishers, 2018) Gozutok, Melike; Basar, Ahmet Ozan; Sasmazel, Hilal TurkogluIn this study, a natural antibacterial substance chitosan was coated with/without potassium sorbate (KS) (0.8% (w/w) of KS, 8% (w/v) chitosan) onto the polypropylene (PP) film by using electrospinning technique to obtain novel antibacterial composite materials for various applications such as wound dressing, tissue engineering, drug delivery and food packaging. Atmospheric pressure plasma surface treatment was applied onto polypropylene films in order to increase its wettability thus enhancing the adhesion capacity of the films and the optimum CA value was determined as 42.75 +/- 0.80 degrees. Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS) analyses were realized to observe the morphological changes and chemical properties of the samples, respectively. Contact angle measurements, tensile testing, oxygen and water vapor transmission rate analyses were performed to obtain wettability values, mechanical properties and WVTRs, respectively. The WVTR was increased by plasma treatment and addition of KS (from 14.264 +/- 0.214% to 21.020 +/- 0.659%). The desired antibacterial performance of the samples was assessed with Staphylococcus aureus and Escherichia coli by inhibition ratio calculation and disc diffusion assay. The highest inhibition ratios were found as 64% for S. aureus and 92% for E. coli for plasma-treated CS-KS-PP films.Article Citation - WoS: 13Citation - Scopus: 14Control of the Crystal Growth Shape in Ch3nh3< Perovskite Materials(Amer Scientific Publishers, 2017) Le, Quyet Van; Shin, Jong Wook; Jung, Jin-Hee; Park, Jongee; Ozturk, Abdullah; Kim, Soo YoungCH3NH3PbBr3 (MAPbBr(3)) materials with perovskite structure were grown by a two-step process using Pb(CH3COO)(2). 3H(2)O and methyl amine bromide (MABr). By changing the concentration of MABr in isopropyl alcohol (IPA) solvent and the annealing temperature, the shape of CH3NH3PbBr3 materials can be controlled to afford nanocubes, nanowires, nanorods, and wrinkled structures. MAPbBr3 with single cubic structure was obtained at a MABr concentration of 3 mg/mL in IPA, and a nanorod array of MAPbBr3 was realized at a MABr concentration of 9 mg/mL in IPA at room temperature. Uniformly wrinkled shapes were formed after the synthesis temperature was increased to 60 and 90 degrees C. The X-ray diffraction patterns, Fourier transform infrared spectra, and X-ray photoelectron spectra of CH3NH3PbBr3 nanorods confirmed that the pure perovskite phase was obtained by dipping Pb(CH3COO)(2). 3H(2)O in MABr/IPA solution. The optical bandgap of the CH3NH3PbBr3 nanorods was estimated from the Tauc plot as 2.2 eV. The evolution of perovskite shapes is expected to lead to improvements in the electrical properties and surface contact, which are important factors for realizing high-performance devices.Article Citation - WoS: 22Antibacterial Performance of Pcl-Chitosan Core-Shell Scaffolds(Amer Scientific Publishers, 2018) Ozkan, Ozan; Sasmazel, Hilal TurkogluIn this study, antibacterial performance of the coaxially electrospun Poly-epsilon-caprolactone (PCL)-chitosan core-shell scaffolds developed, optimized and identified physically and chemically in our previous study, were evaluated for the suitability in wound healing applications. The aim of utilizing a core-shell fibrous scaffold with PCL as core and chitosan as shell was to combine natural biocompatibility, biodegradability and antibacterial properties of chitosan with mechanical properties and resistance to enzymatic degradation of PCL. The scaffolds were prepared with the optimized parameters, obtained from our previous study. Thickness and contact angle measurements as well as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses confirmed repeated fabrication of PCL-chitosan core-shell scaffolds. In this study, assays specific to wound dressing materials, such as water vapor transmission rate (WVTR), in vitro degradability and antibacterial tests were carried out. WVTR value of PCL-chitosan core-shell scaffolds was higher (2315 +/- 3.4 g/m(2).day) compared to single PCL scaffolds (1654 +/- 3.2 g/m(2).day) due to the higher inter-fiber pore size. Additionally, in vitro degradability assays showed that the susceptibility of chitosan to enzymatic degradation can be significantly improved by hybridization with more resistant PCL while still keeping the scaffold to be considered as biodegradable. Finally, inhibition ratio and inhibition zone measurements showed that the PCL-chitosan core-shell polymeric scaffolds had significant antibacterial performance (52.860 +/- 2.298% and 49.333 +/- 0.719% inhibition ratios; 13.975 +/- 0.124 mm and 12.117 +/- 0.133 mm clear inhibition zones, against E. coli and S. aureus, respectively), close to the native chitosan. Therefore, the developed scaffolds can be considered as suitable candidates for biodegradable wound dressing applications.Article Citation - WoS: 3Performance of the Yb/n< Tunneling Barriers(Amer Scientific Publishers, 2018) Qasrawi, A. F.In this article, the design and performance of the CdSe which are deposited onto thin films of Yb metal is reported and discussed. The thin films of CdSe which are deposited by the physical vapor deposition technique are observed to exhibit slightly deformed hexagonal polycrystalline nature with excess amount of Cd as confirmed by the X-ray, energy dispersive X-ray spectroscopy and scanning electron microscopy techniques. The n-type CdSe is also found to form a Schottky barrier of tunneling type when sandwiched between Yb and carbon. The quantum mechanical tunneling mechanism in this device which was tested and modeled in the frequency domain of 10-150 MHz is found to exhibit average intersite separations of similar to 5 nm. The tunneling device exhibited a widening in the depletion region associated with significantly large capacitance tunability in the studied frequency domain. On the other hand, as an optoelectronic device, the Yb/n-CdSe/C Schottky diode exhibited a responsivity of similar to 0.10 NW, photosensitivity of 6.5 x 10(4) and external quantum efficiency of 54% when biased with 1.0 V and exposed to laser light of wavelength of 406 nm.Article Development of Electrospun We43 Magnesium Alloy-Like Compound(Amer Scientific Publishers, 2020) Ozkan, Ozan; Sasmazel, Hilal Turkoglu; Biskin, ErhanMetallic structures are conventionally fabricated with high temperature/deformation processes resulting the smallest possible microscopic structures in the order of several hundreds of micrometer. Therefore, to obtain structures with fibers smaller than 100 Am, those are unsuitable. In this study, electrospinning, a fiber fabrication technique commonly used for polymers, was adopted to fabricate a WE43 magnesium alloy-like fibrous structure. The aim is to adopt metallic WE43 alloy to regenerative medicine using tissue engineering approach by mimicking its composition inside of a fibrous structure. The solution required for electrospinning was obtained with water soluble nitrates of elements in WE43 alloy, and PVP or PVA were added to obtain a spinnable viscosity which was pyrolised away during heat treatment. Electrospinning parameters were optimized with naked-eye observations and SEM as 1.5 g salts and 5 wt.% PVA containing solution prepared at 90 degrees C and electrospun under 30 kV from a distance of 12-15 cm with a feeding rate of 5 mu l/min. Then the samples were subjected to a multi-step heat treatment under argon to remove the polymer and calcinate the nitrates into oxides which was designed based on thermal analyses and reaction kinetics calculations as 6 h at 230 degrees C, 8.5 h at 390 degrees C, 5 h at 465 degrees C, 80 h at 500 degrees C and 10 h at 505 degrees C, consecutively. The characterizations conducted in terms of structure, composition and crystallinity with XRD, XPS, EDX and SEM showed that it is possible to obtain MgaYbNdcZrdOx), (empirical) fibers with the same composition as WE43 in sub-millimeter sizes using this approach.
