Yasin Kanbur

Bioconjugation of hydrogen-bonded organic semiconductors with functional proteins

We demonstrate the direct bioconjugation of hydrogen-bonded organic semiconductors with two different complex functional proteins in an aqueous environment. The representative semiconductors are epindolidione and quinacridone, materials used in devices in the form of vacuum-evaporated polycrystalline films. First, these molecules in thin films react spontaneously with N-hydroxysuccinimide functionalized linkers: disuccinimidyl suberate and succinimidyl biotinate. The suberate linker is then used to covalently bind the Rhodobacter sphaeroides reaction centre (RC), the key photoenzyme for conversion of light into electrical charges in photosynthetic bacteria. Similarly, the biotin linker is used to bridge streptavidin to the surface of the hydrogen-bonded semiconductor film. Multiple-reflection infrared spectroscopy, water contact angle measurements, and atomic force microscopy are used to verify surface functionalization. The presence and functional integrity of the immobilized proteins are demonstrated by specific experiments: a charge recombination kinetics assay in the case of the RC, and photoluminescence measurements for quantum dot-labelled streptavidin. As key results of our work, we have shown that upon bioconjugation, the semiconductors preserve their favourable electrical properties: as evidenced by photoconductor devices operating under water sensitized by the RC, and thin film transistor measurements before and after bioconjugation. These are enabling steps for using hydrogen-bonded semiconductors as platforms for multifunctional bioelectronics devices.

Synthesis and Characterization of Surface Modified Fullerene

Fullerenes were chemically functionalized by using sulphuric acid and nitric acid. The functionalization was done with two different acid ratio. The functionalized nanotubes were characterized with Fourier transform infrared spectroscopy and X-ray photonelectron spectroscopy (XPS), elemental analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Sulfonation of fullerene increased the electrical conductivity of fullerenes up to 0.027 S/cm. TEM micrographs showed that sulfonation improves the dispersion of fullerene in water. Zeta potential measurements also proved this result.

Surface Modification and Characterization of Multi-Walled Carbon Nanotube

Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized by using sulfuric acid and nitric acid. The functionalization was done with two different acid ratio. The functionalized nanotubes were characterized with Fourier Transform Infrared Spectroscopy, X-Ray Photon Spectroscopy, Thermal Gravimetric Analysis, Elemental Analysis, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy. Sulfonation of carbon nanotubes (CN) increased the electrical conductivity of carbon nanotubes up to 1.25 × 10−1 S/cm. The SEM micrographs of the samples showed that CN was observed in more bulky form due to the increasing hyrogen bonding between the particles. The zeta potential of the CN increased with increasing sulfonation amount.

Electrical and Mechanical Properties of Polypropylene/Carbon Black Composites

Polypropylene(PP)/carbon black(CB) composites at different compositions were prepared via melt blending of PP with CB. The effect of CB content on mechanical and electrical properties was studied. Test samples were prepared by injection molding and compression molding techniques. The effect of processing type on mechanical and electrical properties was also investigated. Composites become semi-conductive by addition of 2 wt% CB. The relation between mechanical and electrical properties was discussed. The influence of CB content on morphology and crystallinity was also studied.

Mechanical, electrical, and melt flow properties of polyurethane elastomer/surface-modified carbon nanotube composites:

Carbon nanotube-reinforced polyurethane elastomer composites were prepared by melt-mixing. Nitric acid oxidation and silanization were applied to carbon nanotube surfaces to achieve better interfacial interactions with polyurethane elastomer. Tensile and hardness tests, differential scanning calorimetry, melt flow index test, dielectric measurements, and morphological studies of composites were reported. The best results were obtained for surface-modified carbon nanotubes containing composites with lower loading levels. Addition of carbon nanotubes leads to almost two-fold increase in strain and modulus compared to pristine polyurethane elastomer. Tensile strength of composites was also improved by inclusion of carbon nanotubes. However, strength values drop down with increasing carbon nanotube content. Shore hardness increased with the inclusion of modified carbon nanotube to polyurethane elastomer while pristine carbon nanotube caused remarkable decrease in hardness of polyurethane elastomer. Relatively higher melting points and slightly lower glass transition temperatures were observed for carbon nanotube-loaded composites compared to polyurethane elastomer because of plasticizing effect of carbon nanotube. Incorparation of carbon nanotube to polyurethane elastomer matrix caused reduction in melt flow index values due to formation of agglomarates, and n the contrary, surface modifications of carbon nanotube exhibited increase in melt flow index thanks to enhanced interfacial interactions between carbon nanotube and polyurethane elastomer. Significant increase in dielectric constant of composites was observed. Better dispersion of surface modified carbon nanotubes into polyurethane elastomer was also concluded from SEM micrographs of composites.

Mechanical, physical and morphological properties of acidic and basic pomice containing polypropylene composites

Asidik pomza (AP) ve bazik pomza (BP) polipropilene (PP) eklenmeden once silan baglayici kullanilarak polimer matris ile uyumlu hale getirilmistir. Bunun yani sira, maleik anhidrit asilanmis PP (MA-g-PP) ile kompozitler hazirlanmistir. Kompozitler, buyuk olcekli uretime en uygun yontem olan eriyik karistirma metodu ile laboratuvar olcekli cift vidali ekstruder kullanilarak uretilmistir. Karistiricidan cip formunda elde edilen PP kompozitler, enjeksiyonlu kaliplama teknigi ile sekillendirilmistir. Hazirlanan kompozit numunelerinin mekanik dayanimlari basta olmak uzere su emme testi ile dis hava sartlarinda kullanimlari incelenmistir. Kompozitlere sirasiyla cekme testi, dinamik mekanik analiz (DMA) ve eriyik akis indisi testleri uygulanmistir. Ayrica pomza parcaciklarinin polipropilen matris icinde dagilimini gozlemlemek icin tarayici elektron mikroskobu (SEM) mikrografikleri incelenmistir. Silan ile modifiye edilmis asidik pomza, bazik pomza ve MA-g-PP ile hazirlanan kompozitlerin mekanik ozelliklerinde iyilesmeler saptanmistir. SEM mikrografikleri incelendiginde; silanlanmis pomza iceren ve MA-g-PP matrisli kompozitlerde pomza parcaciklarinin, polimer yuzeyleri ile uyumlu hale geldiginden PP matris icerisinde iyi dagilim gosterdigi belirlenmistir. Ozellikle asidik pomza iceren kompozitlerin erime akis degerlerinde, PP ile kiyaslandiginda belirgin bir degisme olmamistir. Bu sonuc, buyuk olcekteki uygulamalarda pomzanin dolgu maddesi olarak eklenmesiyle polipropilenin islenmesinde onemli bir sorunla karsilasilmayacagi cikarimini desteklemektedir.

Development of multifunctional polyurethane elastomer composites containing fullerene: Mechanical, damping, thermal, and flammability behaviors

Thermoplastic polyurethane (TPU) composites filled with fullerene in the range from 0.5 wt% to 2 wt% were fabricated using melt-compounding. Fullerene addition levels up to nearly twofold increase in tensile strength, percent elongation, and modulus of TPU. The mechanical properties are improved as modified C60 content decreases. Fullerene loadings also enhance thermal stability of TPU. Glass transition temperature decreases by the inclusion of C60 into TPU matrix. Composites exhibited the improvement for storage modulus and vibration-damping behavior. The UL-94 rating and limiting oxygen index value of TPU are also extended to higher values after C60 loadings. Adjuvant effect is observed on fire performance in which pristine C60 inclusions and higher concentrations of C60 exhibit better fire performance. Additions of C60 give identical melt flow index values with that of TPU. Modified C60 particles disperse more homogeneously than pristine ones into TPU matrix because of the improvement in interfacial interactions between fullerene and polyurethane elastomer.

Polipropilen/Huntit Kompozitlerinin Mekanik, Fiziksel ve Morfolojik Özellikleri

Huntit hidromagnezit (HH) polimere eklenmeden once, silan baglayici kullanilarak polipropilen (PP) matris ile uyumlu hale getirilmistir. Buna ek olarak, HH ile uyumlu olmasi amaciyla maleik anhidrit asilanmis PP (Ma-g-PP) matrisi ile de kompozitler olusturulmustur. Kompozit malzemeler, sanayide en sik tercih edilen yontem olan eriyik karistirma metodu ile laboratuvar olcekli cift vidali ekstruder kullanilarak, % 10 HH icerecek sekilde hazirlanmistir. Granul haline getirilen kompozitler enjeksiyonlu kaliplama yontemi ile sekillendirilmistir. Hazirlanan kompozitlere sirasiyla cekme testi, dinamik mekanik analiz (DMA) ve erime akis indisi testleri uygulanmistir. Numunelerin mekanik dayanimlarina ek olarak, dis hava sartlarinda kullanimini belirlemek amaciyla su emme testleri gerceklestirilmistir. Ayrica toz parcaciklarin polipropilen matris icinde dagilimini gozlemlemek amaciyla tarayici elektron mikroskobu (SEM) kullanilmistir. Sonuclar incelendiginde, silanlanmis HH ve Ma-g-PP kullanimi ile elde edilen kompozitlerin mekanik ozelliklerinde iyilesme gozlemlenmistir. SEM goruntuleri incelendiginde, silanlama islemine tabi tutulmus huntit ve Ma-g-PP kompozitlerinde huntit parcaciklarinin PP matris icerisinde iyi dagilim gosterdigi ve parcacik ile polimer yuzeylerinin uyumlu oldugunu gorulmektedir. Bu sonuc mekanik ozelliklerdeki iyilesmeyi desteklemektedir. Kompozitlerin erime akis degerlerinde belirgin bir degisme olmamistir. Bu sonuc, PP matrisine huntit dolgu maddesi eklenmesiyle polimerin islenmesinde onemli bir sorunla karsilasilmayacagini gostermektedir.

Investigating mechanical, thermal, and flammability properties of thermoplastic polyurethane/carbon nanotube composites

Thermoplastic polyurethane (TPU) composites containing carbon nanotube (CNT) with the loading ratios from 0.5wt% to 2 wt% were prepared using melt-compounding process. Surfaces of the CNT particles were treated with sulfuric acid/nitric acid to purify CNT and to achieve compatible surface characteristics between TPU matrix and CNT. Mechanical, thermal, flame retardant, melt flow, and morphological properties of TPU/CNT composites were investigated. Addition of CNT to TPU matrix causes in a prominent increase in tensile strength, percentage of elongation at break, and tensile modulus values of TPU. The mechanical properties are improved for lower modified CNT loadings. CNT inclusions also improve the thermal stability of pristine TPU. Addition of CNT into TPU matrix causes increase in melting and decomposition temperatures of TPU and decrease in glass transition temperature. The flammability parameters of TPU also shift to higher values after CNT loadings to matrix. Modified CNT additions at higher concentrations exhibit better fire performance. Additions of modified CNT and pristine CNT show different trends in the case of melt flow rate values. Modified CNTs disperse more homogeneously relative to pristine ones into TPU matrix which is due to improvement in interfacial interactions between CNT and TPU.