Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 3Citation - Scopus: 5Physically Unclonable Security Patterns Created by Electrospinning, and Authenticated by Two-Step Validation Method(IOP Publishing, 2022) Taşcıoğlu, Didem; Atçı, Arda; Sevim Ünlütürk, Seçil; Özçelik, SerdarCounterfeiting is a growing economic and social problem. For anticounterfeiting, random and inimitable droplet/fiber patterns were created by the electrospinning method as security tags that are detectable under UV light but invisible in daylight. To check the authenticity of the original security patterns created; images were collected with a simple smartphone microscope and a database of the recorded original patterns was created. The originality of the random patterns was checked by comparing them with the patterns recorded in the database. In addition, the spectral signature of the patterns in the droplet/fiber network was obtained with a simple and hand-held spectrometer. Thus, by reading the spectral signature from the pattern, the spectral information of the photoluminescent nanoparticles was verified and thus a second-step verification was established. In this way, anticounterfeiting technology that combines ink formula, unclonable security pattern creation and two-level verification is developed.Article Citation - WoS: 14Citation - Scopus: 16Bodipy-Based Organic Color Conversion Layers for Wleds(Elsevier, 2020) Yüce, Hürriyet; Güner, Tuğrul; Dartar, Suay; Kaya, Beraat Umur; Emrullahoğlu, Mustafa; Demir, Mustafa MuammerThe usage of organic dyes in phosphor conversion layer of WLED is an attractive approach since they have high molar extinction coefficient and photostability. Various types of organic pigments have been employed for this purpose such as BODIPY, perylene diimide, Rhodamine B, pyrene, Nile red, etc. Among those, BODIPY-based organic dyes appear to be promising candidate for white light generation. In this work, for the first time, red and green emitting BODIPY-based organic molecules have been used as colour conversion layer. These molecules were associated with PMMA in DMF solution and the resulting solution was subjected to electrospinning. Colorful electrospun mats were embedded into PDMS matrix and their free-standing PDMS composite films were used as color conversion layers over blue LED to produce white light such that CRI of 95 and CCT of 4200 K was achieved. These values show that BODIPY-based organic molecules containing fiber composites are promising candidates to be used as color conversion layers for white light applications.Article Citation - WoS: 25Citation - Scopus: 27Osteogenic Differentiation of Mesenchymal Stem Cells on Random and Aligned Pan/Ppy Nanofibrous Scaffolds(SAGE Publications, 2019) Selamet, Yusuf; İnce Yardımcı, Atike; Baskan, Öznur; Yılmaz, Selahattin; Meşe, Gülistan; Özçivici, EnginThe aim of this study was to develop random and aligned polyacrilonitrile (PAN)/polypyrrole (PPy) nanofibrous scaffolds by electrospinning technique for osteogenic differentiation of mesenchymal stem cells. Nanofibers were fabricated successfully as straight, smooth, and free from bead formation. The average diameter of random and aligned nanofibers was 268(+/- 49) nm and 225(+/- 72) nm, respectively. Alignment process increased the tensile strength of nanofibers 3.9-fold, while the tensile strain of nanofibers decreased by 78%. PAN/PPy nanofibers were hydrophilic with the contact angle value of about 32 degrees and alignment did not affect the contact angle value. Random and aligned PAN/PPy nanofibers were investigated as a scaffold material for osteogenic differentiation of D1 ORL UVA mouse bone marrow mesenchymal stem cells. Cells were able to attach and grow on nanofibers confirmed by cell viability results. Stem cells that were cultured with osteogenic induction were able to mineralize on electrospun nanofibers based on alizarin red and Von Kossa dye staining. For aligned PPy nanofibers, mineralization occurred in the fiber alignment direction. Consequently, PAN/PPy nanofibrous mats in both random and aligned forms would be potential candidates for bone tissue engineering.Article Citation - WoS: 18Citation - Scopus: 14Optimization and Performance of Nitrogen-Doped Carbon Dots as a Color Conversion Layer for White-Led Applications(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2019) Güner, Tuğrul; Yüce, Hürriyet; Taşçıoğlu, Didem; Şimşek, Eren; Savacı, Umut; Genç, Aziz; Demir, Mustafa MuammerIn this study, green-emitting nitrogen-doped carbon dots (N-CDots) were synthesized and incorporated into drop-cast composite films for use as color conversion layers in a white-LED configuration to generate white light. In order to resolve the red deficiency of this configuration, a commercial red phosphor was integrated into the system. Moreover, the N-CDots were also processed into polymer/N-CDot composite fibers, for which we determined the amount of N-CDots that yielded adequate white-light properties. Finally, we showed that white light with excellent properties could be generated by employing both of the fabricated N-CDot composites either as drop-cast films or composite fibers. Hence, N-CDots provide a promising alternative to inorganic phosphors that are commonly employed in white-LED configurations.Article Citation - WoS: 39Citation - Scopus: 39Polarized Emission From Cspbbr3 Nanowire Embedded-Electrospun Pu Fibers(IOP Publishing Ltd., 2018) Güner, Tuğrul; Topçu, Gökhan; Savacı, Umut; Genç, Aziz; Sarı, Emre; Demir, Mustafa MuammerInterest in all-inorganic halide perovskites has been increasing dramatically due to their high quantum yield, band gap tunability, and ease of fabrication in compositional and geometric diversity. In this study, we synthesized several hundreds of nanometer long and ∼4 nm thick CsPbBr3 nanowires (NWs). They were then integrated into electrospun polyurethane (PU) fibers to examine the polarization behavior of the composite fiber assembly. Aligned electrospun fibers containing CsPbBr3 NWs showed a remarkable increase in the degree of polarization from 0.17-0.30. This combination of NWs and PU fibers provides a promising composite material for various applications such as optoelectronic devices and solar cells.Article Citation - WoS: 24Citation - Scopus: 30Solution Electrospinning of Polypropylene-Based Fibers and Their Application in Catalysis(Korean Fiber Society, 2016) Berber, Emine; Horzum, Nesrin; Hazer, Bakí; Demir, Mustafa MuammerSince the dissolution of polyolefins is a chronic problem, melt processing has been tacitly accepted as an obligation. In this work, polypropylene (PP) was modified on molecular level incorporating poly(ethylene glycol) (PEG) as graft segment (PP-g-PEG) in a range of 6 to 9 mol%. Gold nanoparticles were nucleated in the presence of the copolymer chains via redox reaction. The dissolution of the amphiphilic comb-type graft copolymers containing gold nanoparticles (80 nm in diameter) was achieved in toluene and successfully electrospun from its solution. The diameter of composite fibers was in the range from 0.3 to 2.5 μm. The design of the structurally organized copolymer fiber mats provided a support medium for the nanoparticles enhancing the active surface area for the catalytic applications. The resulting composite fibers exhibited rapid catalytic reduction of methylene blue (MB) dye in the presence of sodium borohydride (NaBH4) compared to corresponding composite cast film.Article Citation - WoS: 6Citation - Scopus: 6Investigation of the Spontaneous Emission Rate of Perylene Dye Molecules Encapsulated Into Three-Dimensional Nanofibers Via Flim Method(Springer Verlag, 2014) Açıkgöz, Sabriye; Demir, Mustafa Muammer; Yapaşan, Ece; Kiraz, Alper; Ünal, Ahmet A.; İnci, Mehmet NaciThe decay dynamics of perylene dye molecules encapsulated in polymer nanofibers produced by electrospinning of polymethyl methacrylate are investigated using a confocal fluorescence lifetime imaging microscopy technique. Time-resolved experiments show that the fluorescence lifetime of perylene dye molecules is enhanced when the dye molecules are encapsulated in a three-dimensional photonic environment. It is hard to produce a sustainable host with exactly the same dimensions all the time during fabrication to accommodate dye molecules for enhancement of spontaneous emission rate. The electrospinning method allows us to have a control over fiber diameter. It is observed that the wavelength of monomer excitation of perylene dye molecules is too short to cause enhancement within nanofiber photonic environment of 330 nm diameters. However, when these nanofibers are doped with more concentrated perylene, in addition to monomer excitation, an excimer excitation is generated. This causes observation of the Purcell effect in the three-dimensional nanocylindrical photonic fiber geometry.Article Citation - WoS: 6Citation - Scopus: 6Hierarchial Coassembly of a Cyanine Dye in Poly(vinyl Alcohol) Fibrous Films by Electrospinning(American Chemical Society, 2013) Demir, Mustafa Muammer; Horzum, Nesrin; Özen, Bengisu; Özçelik, SerdarWe report molecular aggregate formation of TTBC (1,1′,3,3′- tetraethyl-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine) in submicrometer-sized PVA (poly(vinyl alcohol)) fibers by electrospinning. The formation of the molecular aggregate is examined by solution and instrumental parameters of electrospinning. The precursor solution of PVA/TTBC, in the range of 0.016-0.065 wt % is subjected to electrospinning under an electrical field ranging from 0.95 to 1.81 kV cm-1. Both randomly deposited and uniaxially aligned fibers are achieved by using two parallel-positioned metal strips as counter electrode. Photoluminescence and polarized Fourier transform infrared spectroscopies are employed to determine spectral properties of the fibers. H-aggregates are formed within the electrospun fibers, regardless of their alignment, and H- and J-type aggregates coexist in the alternative spin-coated and the cast films. A strongly polarized photoluminescence emission is observed in the direction of uniaxially aligned fibers as a result of the orientation of the H-aggregates along the fiber axis. We demonstrate that electrospinning is a process capable of forming and orienting TTBC aggregates during the structural development of the polymer/dye nanofibers. These fibrous films may potentially find applications in optics and electronics.