Browsing by Author "Parlak, Onur"

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Citation - WoS: 12
Citation - Scopus: 14
Anomalous transmittance of polystyrene-ceria nanocomposites at high particle loadings
(Royal Soc Chemistry, 2013) Parlak, Onur; Demir, Mustafa M.; Demir, Mustafa
Optical nanocomposites based on transparent polymers and nanosized pigment particles have usually been produced at low particle concentrations due to the undesirable optical scattering of the pigment particles. However, the contribution of the particles to many physical properties is realized at high concentrations. In this study, nanocomposites were prepared with transparent polystyrene (PS) and organophilic CeO2 nanoparticles using various compositions in which the particle content was up to 95 wt%. The particles, capped by 3-methacryloxypropyltrimethoxysilane (MPS), were dispersed into PS and the transmittance of the spin-coated composite films was examined over the UV-visible region. When the particle concentration was <20 wt%, the transmittance of the films showed a first-order exponential decay as the Rayleigh scattering theory proposes. However, a positive deviation was observed from the decay function for higher particle contents. The improvement in transmittance may be a consequence of interference in the multiple scattering of light by the quasi-ordered internal microstructure that gradually develops as the particle concentration increases.
Fabrication of transparent polymer nanocomposites containing pmma-grafted CeO2 particles
(Izmir Institute of Technology, 2011) Parlak, Onur; Demir, Mustafa; Demir, Mustafa Muammer
The composite materials prepared by transparent polymer and nanosized particles possess promising future in optical design and applications since their controllable optical properties. In this study, transparent/translucent composite films based on polystyrene (PS) and poly(methyl methacrylate) (PMMA)-grafted CeO2 nanoparticles were prepared. CeO2 nanoparticles were precipitated from Ce(NO3)3·6H2O and urea in dimethyl formamide at 120°C. The surface of the nanoparticles was modified with a polymerizable surfactant, 3-methacyloxypropyltrimethoxy silane (MPS) in situ at 0°C. The size of the particles was fixed to 18 nm in diameter. The particles were dispersed into a mixture of MMA:toluene solution. The free radical solution polymerization was carried out in situ at 60°C using benzoyl peroxide (BPO) as initiator. A PMMA layer is formed around CeO2 nanoparticles. The thickness of the shell ranged from 9 to 84 nm was controlled by the amount of BPO using 6 and 0.5 wt %, respectively with respect to monomer. The layer thickness was found to be inversely proportional with the amount of initiator. The resulting PMMA-grafted CeO2 particles were blended with PS in tetrahydrofuran and the solution was spin-coat on a glass slide. CeO2 content in the composite films was fixed to 5.5 wt %. The transmission of the films was examined by UV-vis spectroscopy. The transmission of the PS composite prepared by neat CeO2 particles was 71 %. It was increased to 85 % when the composite prepared with PMMA-grafted CeO2 particles whose PMMA thickness is 9 nm. We believe that the achievement in transparency is most probably due to the reduction in refractive index mismatch between CeO2 particles and PS matrix using PMMA layer at interface.
Citation - WoS: 20
Citation - Scopus: 23
Null Extinction of Ceria@silica Hybrid Particles: Transparent Polystyrene Composites
(Amer Chemical Soc, 2015) Incel, Anil; Guner, Tugrul; Parlak, Onur; Demir, Mustafa M.; Demir, Mustafa
Scattering of light in optical materials, particularly in composites based on transparent polymer and inorganic pigment nanopartides, is a chronic problem. It might originate mainly from light scattering because of a refractive index mismatch between the particles and transparent polymer matrix. Thus, the intensity of light is rapidly diminished and optical transparency is reduced. Refractive index matching between the pigment core and the surrounding transparent matrix using a secondary component at the interface (shell) has recently appeared as a promising approach to alter light scattering. Here, CeO2 (ceria) nanopartides with a diameter of 25 nm are coated with a SiO2 (silica) shell with various thicknesses in a range of 6.5-67.5 nm using the Stober method. When the hybrid core shell particles are dispersed into transparent polystyrene (PS), the transmission of the freestanding PS composite films increases over both the ultraviolet (UV) and visible region as the shell thickness increases particularly at 37.5 nm. The increase of transmission can be attributed to the reduction in the scattering coefficient of the hybrid particles. On the other hand, the particles in tetrahydrofuran (THF) absorb over UV and the intensity of absorption shows a systematic decrease as the shell thickness increases. Thus, the silica shell suppresses not only the scattering coefficient but also the molar absorptivity of the core ceria particles. The experimental results regarding the target shell thickness to develop low extinction (scattering + absorption) composites show a qualitative agreement with the predictions of Effective Medium Theory.
Citation - WoS: 105
Citation - Scopus: 112
Synthesis of amidoximated polyacrylonitrile fibers and its application for sorption of aqueous uranyl ions under continuous flow
(Elsevier Science Sa, 2012) Horzum, Nesrin; Shahwan, Talal; Parlak, Onur; Demir, Mustafa M.; Demir, Mustafa
This study reports a feasible method for the removal of radioactive U(VI) ions from aqueous systems via column sorption under continuous flow. Electrospun polyacrylonitrile (PAN) fibers were used as sorbent materials in a homemade minicolumn. The nitrite groups on the fibers' surface were modified to amidoxime groups using hydroxylamine hydrochloride. Surface modification was observed to enhance the sorption capacity of PAN fibers toward uranium ions by more than 4-fold by virtue of the chelating ability of the amidoxime groups. The experiments investigated the effect of pH, initial concentration, and repetitive loading on the sorption properties of amidoximated PAN fibers. Based on the overall results, the surface-modified fibers seem to be a suitable potential sorbent material for applications in environmental cleanup, particularly for nuclear plants. (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 70
Toward Transparent Nanocomposites Based on Polystyrene Matrix and PMMA-Grafted CeO₂ Nanoparticles
(Amer Chemical Soc, 2011) Parlak, Onur; Demir, Mustafa M.; Demir, Mustafa
The association of transparent polymer and nanosized pigment particles offers attractive optical materials for various potential and existing applications. However, the particles embedded into polymers scatter light due to refractive index (RI) mismatch and reduce transparency of the resulting composite material. In this study, optical composites based on polystyrene (PS) matrix and poly(methyl methacrylate) (PMMA)-grafted CeO2 hybrid particles were prepared. CeO2 nanoparticles with an average diameter of 18 +/- 8 nm were precipitated by treating Ce(NO3)center dot 6H(2)O with urea in the presence of a polymerizable surfactant, 3-methacyloxypropyltrimethoxy silane. PMMA chains were grafted on the surface of the nanoparticles upon free radical in situ solution polymerization. While blending of unmodified CeO2 particles with PS resulted in opaque films, the transparency of the composite films was remarkably enhanced when prepared by PMMA-grafted CeO2 hybrid particles, particularly those having a PMMA thickness of 9 nm. The improvement in transparency is presumably due to the reduction in RI mismatch between CeO2 particles and the PS matrix when using PMMA chains at the interface.