Yazar "Cengiz, Ugur" seçeneğine göre listele

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    Applicability of Cassie-Baxter equation for superhydrophobic fluoropolymer silica composite films
    (Elsevier, 2015) Cengiz, Ugur; Cansoy, C. Elif
    In this study, surface topographies and wettabilities of flat and composite rough films of perfluoro-styrene (TM/S) random copolymers with silica particles were investigated. The water and oil repellencies of flat TM/S copolymer and rough silica-TM/S composite surfaces were studied with varying perfluoro and silica contents. Increase in silica content resulted in an increase in water contact angle values; water contact angle values increased from 113 up to 170, and the resultant surfaces were showing extremely superhydrophobic behavior depending on their silica contents. However a decrease in hexadecane contact angles from 61 to 25 depending on both silica %wt and perfluoro content of the TM/S copolymer was seen. Applicability of Cassie-Baxter equation was also investigated for TM/S copolymer films with silica particles. The results showed that Cassie-Baxter equation cannot be used for superhydrophobic surfaces, however, can be applied to oleophilic surfaces with caution. The oil repellencies of TM/S flat films in the terms of contact angle hysteresis was also compared with perfluoroethyl alkyl methacrylate-methyl methacrylate copolymer (TM/MMA) by using oil drops with varying surface tensions between 20.9 mN/m and 26.9 mN/m. The surface oleophobicities were changed according to the characteristics of the functional groups of MMA and S. The dependency of work of adhesion results of TM/S flat surfaces on wt.% of perfluoroalkyl content was also examined. (C) 2015 Elsevier B.V. All rights reserved.
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    Bioplastic Production from Microalgae: A Review
    (Mdpi, 2020) Cinar, Senem Onen; Chong, Zhi Kai; Kucuker, Mehmet Ali; Wieczorek, Nils; Cengiz, Ugur; Kuchta, Kerstin
    Plastic waste production around the world is increasing, which leads to global plastic waste pollution. The need for an innovative solution to reduce this pollution is inevitable. Increased recycling of plastic waste alone is not a comprehensive solution. Furthermore, decreasing fossil-based plastic usage is an important aspect of sustainability. As an alternative to fossil-based plastics in the market, bio-based plastics are gaining in popularity. According to the studies conducted, products with similar performance characteristics can be obtained using biological feedstocks instead of fossil-based sources. In particular, bioplastic production from microalgae is a new opportunity to be explored and further improved. The aim of this study is to determine the current state of bioplastic production technologies from microalgae species and reveal possible optimization opportunities in the process and application areas. Therefore, the species used as resources for bioplastic production, the microalgae cultivation methods and bioplastic material production methods from microalgae were summarized.
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    Fabrication and application of superhydrophilic antifog surface by sol-gel method
    (Elsevier Science Sa, 2019) Kaya, Ayse Senem Topcu; Cengiz, Ugur
    Herein, we report a single step and a one pot by using spin coating method for the preparation of optically transparent, superhydrophilic, antifogging composite surface. The wettability performance and also antifogging properties of these surfaces were investigated depending on silica particles content in composite solution. It was also examined the effects of production technique changes on wettability and antifogging characteristics of these surfaces having 20% wt silica particles content. The apparent water contact angle of transparent surfaces were found to vary between 65 degrees and 4 degrees depending on the silica content, polymer type and production technique. Superhydropilic surface (WCA = 4 degrees) displayed a good antifogging performance and light permeability behavior. It was also observed that antifogging behavior kept showing when water contact angle is lower than 15 degrees. However, antifogging properties disappeared when water contact angle is higher than 25 degrees. These results were showed that one step-one pot reaction have a better results than two step reactions depending on silica particles adding time.
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    Perfluoromethacrylate-styrene statistical copolymers synthesized in CO2-expanded monomers
    (Springer, 2014) Cengiz, Ugur; Erbil, H. Yildirim
    Statistical copolymers of perfluoroalkyl ethyl methacrylate (Zonyl-TM) and styrene (S) were synthesized in CO2-expanded monomer medium at a low initial pressure of 25 MPa. Different Zonyl-TM/S feed ratios were used during copolymerizations, and it was determined that the increase in the Zonyl-TM content and decrease of the CO2 amount in the comonomer feed resulted in a decrease of the molecular weights of copolymers due to earlier precipitation of copolymers giving shorter chains. The cloudy CO2-expanded liquid monomer phase was found to be the main loci of copolymerization. In addition, the increase in the Zonyl-TM feed ratio resulted in an increase in the critical degree of the polymerization time (J (crit)) as the time when the copolymer chains start to precipitate. The higher the Zonyl-TM content used in the feed, the higher the J (crit) time and the lower the weight-average molecular weight (M (w)) of the copolymer obtained. Thermal analysis results of the copolymer indicated that the copolymers are stable up to 387-403 A degrees C.
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    Preparation of stable, transparent superhydrophobic film via one step one pot sol-gel method
    (Springer, 2018) Topcu, Ayse Senem Kaya; Erdogan, Edanur; Cengiz, Ugur
    Herein, we report a single step and a one pot by using spin coating method for the preparation of optically transparent superhydrophobic TEOS-silica composite films. Silica sols were prepared by keeping the molar ratio of TEOS/CH3OH/H2O (0.1 M NH4F) constant at 1:33.15:6.06, respectively. Increasing the silica content of the coating solution resulted in decreasing the transparency of the composite films from 93 to 84% (in references to 93% transmission defined by a plain glass substrate). The static water and hexadecane contact angle of transparent surfaces were found to vary between 65A degrees and 170A degrees (sliding angle < 3A degrees) and 45A degrees to 5A degrees (sliding angle = 15A degrees) depending on the silica content. The stability of the surface remained nearly constant for several months under stored at ambient conditions. The mechanical stability of the prepared of TEOS-silica composite was tested by scratching and adhesive tape test. For the chemical test applications, NaOH, HCl, and H2SO4 were used for the TEOS-silica composite films.
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    Solvent-Free Synthesis of a Superamphiphobic Surface by Green Chemistry
    (Amer Chemical Soc, 2019) Ozbay, Salih; Cengiz, Ugur; Erbil, H. Yildirim
    A superamphiphobic surface having both water and oil repellence was prepared by applying a solvent-free surface coating method using liquid-CO2 in the scope of green chemistry. Poly(perfluoroalkyl ethyl acrylate) homo- polymer was synthesized by a free radical polymerization in supercritical CO2 medium. This polymer was dissolved in liquid-CO2 containing hydrophilic nanosilica particles in a stirred stainless steel reactor at room temperature under a low CO2 pressure. The polymer/nanosilica dispersion was used to coat glass slides located horizontally in a stainless steel tube by using the free meniscus coating method. A series of superamphiphobic coatings were formed under different coating conditions with the variation of polymer/nanosilica concentrations, the types of nanosilica powders, system pressures, and degassing flow rates. The highest apparent water contact angle was 173 degrees and the hexadecane contact angle was 169 degrees on these superamphiphobic hybrid coatings with roll-off angles that were <7 degrees. Such superamphiphobic surfaces have a large potential in biomedical applications for the preservation of small amounts of bioliquids during analysis. In a parallel study, a superhydrophobic surface without containing any nanosilica powder was also obtained by applying the rapid expansion supercritical solution method. Polyperfluoroacrylate polymer was dissolved in supercritical CO2 and was sprayed onto glass slides that were previously coated with a polyacrylate adhesive layer. The water contact angles were larger than 170 degrees on this superhydrophobic coating. To optimize the coating conditions, the cloud point pressures of polyperfluoroacrylate polymer in sc-CO2 were determined at various polymer concentrations and temperatures for this purpose.
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    Superhydrophobic perfluoropolymer surfaces having heterogeneous roughness created by dip-coating from solutions containing a nonsolvent
    (Elsevier Science Bv, 2014) Cengiz, Ugur; Erbil, H. Yildirim
    Superhydrophobic and oleophobic rough copolymer surfaces containing micro- and nano-hierarchical ball-like islands having diameters between 100 nm and 7 mu m were formed using styrene-perfluoromethacrylate random copolymers which were dip-coated on glass slides from THF and MEK mixture containing methanol as nonsolvent. These copolymers were synthesized in a CO2-expanded monomer medium at 250 bar pressure and 80 degrees C. The sizes of the micro-islands can be controlled by varying the copolymer composition; and the degree of phase separation by adjusting the solvent/non-solvent ratio. Flat and lotus-like hierarchical surfaces of the copolymers were characterized using contact angle measurements and SEM. The increase in the perfluoromethacrylate content of the flat copolymers resulted in a decrease of the total surface free energy of the flat copolymer surfaces from 18.3 down to 14.2 mJ/m(2). The increase in the methanol non-solvent fraction resulted in decrease of the micro-island diameter from 7 mu m down to 100 nm and the water contact angle increased from 117 degrees up to 160 degrees and hexadecane from 65 degrees up to 90 degrees. (C) 2013 Elsevier B.V. All rights reserved.
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    Superhydrophobic perfluoropolymer/polystyrene blend films induced by nonsolvent
    (Elsevier Science Bv, 2016) Gengec, Nevin Atalay; Cengiz, Ugur; Erbil, H. Yildirim
    Statistical copolymers of perfluoroalkyl ethyl acrylate (Zonyl-TAN) and methyl methacrylate (MMA) were synthesized in a CO2 polymerization system where a CO2-expanded monomer mixture was formed at 13 MPa, and 80 degrees C by using AIBN as initiator. Flat and superhydrophobic surfaces were subsequently prepared on glass slides by applying a phase separation process where the synthesized p(TAN-co-MMA) copolymer and polystyrene (PS) were dissolved in THE solvent. Ethanol was added as the non-solvent to introduce superhydrophobicity during film formation. Water contact angle on the flat p(TAN-co-MMA) copolymer was 118 degrees and increased up to 170 degrees with the formation of surface roughness. The ratio of the ethanol non-solvent in the blend solution has an important effect on the magnitude of surface roughness during the phase separation process. Both pits and protrusions of 1-10 mu m in size were formed on the surface when non-solvent was used. Surface roughness increased with the increase in the ethanol ratio and the PS content of the blend solution. (C) 2016 Elsevier B.V. All rights reserved.
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    Synthesis of Silica-Based Boron-Incorporated Collagen/Human Hair Keratin Hybrid Cryogels with the Potential Bone Formation Capability
    (Amer Chemical Soc, 2021) Cal, Fatma; Sezgin Arslan, Tugba; Derkus, Burak; Kiran, Fadime; Cengiz, Ugur; Arslan, Yavuz Emre
    Tissue engineering and regenerative medicine have evolved into a different concept, the so-called clinical tissue engineering. Within this context, the synthesis of next-generation inorganic-organic hybrid constructs without the use of chemical crosslinkers emerges with a great potential for treating bone defects. Here, we propose a sophisticated approach for synthesizing cost-effective boron (B)- and silicon (Si)-incorporated collagen/hair keratin (B-Si-Col-HK) cryogels with the help of sol-gel reactions. In this approach, collagen and hair keratin were engaged with a B-Si network using tetraethyl orthosilicate as a silica precursor, and the obtained cryogels were characterized in depth with attenuated total reflectance-Fourier transform infrared spectroscopy, solid-state NMR, X-ray diffraction, thermogravimetric analysis, porosity and swelling tests, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda analyses, frequency sweep and temperature-dependent rheology, contact angle analysis, micromechanical tests, and scanning electron microscopy with energy dispersive X-ray analysis. In addition, the cell survival and osteogenic features of the cryogels were evaluated by the MTS test, live/dead assay, immuno/histochemistry, and quantitative real-time polymerase chain reaction analyses. We conclude that the B-Si-networked Col-HK cryogels having good mechanical durability and osteoinductive features would have the potential bone formation capability. © 2021 American Chemical Society.
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    The effect of pattern sizes on oleophobicity and superhydrophobicity of micropatterned surfaces
    (Elsevier Science Sa, 2016) Cengiz, Ugur; Cansoy, C. Elif
    In this study, cylindrical pillars with varying diameters between 10 mu m to 100 mu m, seperation distances between 5 mu m to 10 mu m, constant heights of 40 mu m +/- 2 and solid area fractions [f(s)(CB) (geo)] between 0.349 to 0.712 were prepared by deep reactive ion etching process and all surfaces were hydropho-bized/oleophobized by coating with perfluoro-styrene (TM/S) random copolymer that was synthesized in CO2-expanded monomer. It was found that, oleophobic behaviors of the patterned surfaces were affected from the type of the hydrocarbon liquids used and with the increase of hydrocarbon liquid chain lengths cylindrical pillar surfaces exhibited more oleophobic behavior. Pattern sizes also affected both oil and water drop CA values however oil and water drops behaved oppositely on the pillar surfaces. Applicability of Cassie-Baxter equation on cylindrical pillar surfaces was also investigated and was found that CA values of both water and hydrocarbon liquids were not obeying Cassie-Baxter theory however in the case of hydrocarbon liquids deviations from the theory were much more larger. (C) 2016 Elsevier B.V. All rights reserved.
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    The effect of perfluoroalkyl and hydrocarbon liquid chain lengths on oleophobic behaviors of copolymer surfaces
    (Elsevier Science Bv, 2014) Cansoy, C. Elif; Cengiz, Ugur
    In this work, the effect of wt.% of perfluoroalkyl content and also hydrocarbon chain length on oleophobic properties of perfluoroethyl alkyl methacrylate-methyl methacrylate (Zonyl-TM-MMA) copolymers was investigated. The wetting performance of p(Zonyl-TM-ran-MMA) copolymer films by hydrocarbon liquids was found to be strongly depended on perfluoroalkyl chain lengths. Besides, increase in hydrocarbon chain length also caused an increase in contact angle results of p(Zonyl-TM-ran-MMA) copolymer films due to the stronger cohesion interactions of liquid molecules and this resulted in weaker adhesion interactions between copolymer surface and hydrocarbon drop. It was also discovered that contact angle hysteresis, Delta cos theta, values of copolymers depend on both wt.% Zonyl-TM content and also hydrocarbon chain length of liquids. (C) 2013 Elsevier B.V. All rights reserved.
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    The lifetime of floating liquid marbles: the influence of particle size and effective surface tension
    (Royal Soc Chemistry, 2013) Cengiz, Ugur; Erbil, H. Yildirim
    In this study, we investigated the factors affecting the lifetime of liquid marbles placed on a glass surface and floating on water It was found that the particle size, surface free energy and hydrophobicity of the encapsulating microparticles determine the effective surface tension and lifetime of a liquid marble floating on water We formed liquid marbles using ultra-hydrophobic poly(perfluoroalkyl ethyl acrylate) powder with three different particle sizes (8 +/- 1, 20 +/- 2 and 60 +/- 5 mu m) and polytetrafluoroethylene powder (7 +/- 2 mu m). It was found that both the effective surface tension and lifetime of a floating liquid marble increased considerably with the decrease in the particle size of the ultra-hydrophobic poly(perfluoroalkyl ethyl acrylate) powder We also determined that a floating liquid marble had a longer lifetime if the water contact angle of the polymer powder was high and its surface free energy was low by comparing the results of two different powders having very close average particle sizes but different hydrophobicities.