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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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    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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    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.