Production of PEG grafted PAN copolymers and their electrospun nanowebs as novel thermal energy storage materials

This paper deals with the synthesis of poly(ethylene glycol) (PEG) grafted poly(acrylo nitrile) (PAN) copolymers as novel solid-solid phase change materials via two step free radical polymerization reaction. The structural and thermal characterizations of the synthesized copolymers, namely PEG1500-g-PAN, PEG2000-g-PAN, PEG4000-g-PAN, PEG10000-g-PAN and PEG35000-g-PAN, were performed by Fourier transform infrared spectroscopy, Nuclear magnetic resonance spectrometry, differential scanning calorimetry and thermogravimetry. They were thermally stable and had the capability of absorbing and releasing great amount of heat ranging between 70 and 126 Jg-1 at the temperature interval of 40‒65 oC during heating and successive cooling cycles. To transform the PEG-g-PAN copolymers into the assemblies appropriate for thermal energy storage (TES) systems, thermo-regulating PEG-g-PAN nanowebs were also produced by means of coaxial electrospinning. The SEM images of PEG-g-PAN nanowebs displayed that they were all composed of hollow cylindrical ultrafine fibers with the average diameters ranging in 175‒277 nm. During the differential scanning calorimetry measurements, those nanowebs demonstrated repeatable solid-solid phase change with the heat storage capacities varying between 35 and 75 Jg-1 at the same temperature interval with the corresponding PEG-g- PAN copolymers. The PEG-g-PAN copolymers and their electrospun nanowebs can be promising TES materials and can have convenient industrial applications

Synthesis And Characterization Of New Generation Polymeric Additives For Cem I Cement Mortar

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2010Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2010Yapı endüstrisinin en temel malzemesi olan kompozit materyal beton, çimentonun ince ve iri agrega ve suyla karıştırılmasıyla elde edilir. Betonun özellikleri, öncelikle su ve çimento arasında meydana gelen ve betonun sertleşmesi süresince devam eden kimyasal reaksiyonlar ile saptanır. Ayrıca kimyasal katkılar ve ek çimento materyalleri arasındaki etkileşim de plastik (taze) ve sertleşmiş betonun üzerinde oldukça etkilidir. Bu çalışmada, çimentonun plastikliğini ve performansını arttırmak için polar grup graft edilmiş polar polimer bazlı yeni polimerik katkılar sentezledik. Ana zincir olarak polietilen glikol 6000 (PEG6000) ve poli itakonik asit (PIA) seçildi. Sentezlenen polimerik katkıların karakterizasyonu TS EN 480-1 standardına göre yapıldı. Sonuçlar, harç üzerinde fonksiyonlandırılmış PIA örneklerinin, fonksiyonlandırılmış PEG6000 örneklerinden daha etkili olduğunu gösterdi.Concrete is a basic building materials for construction which is a composite material produced when cement is mixed with fine and coarse aggregates and water. The properties of concrete are primarily determined by the chemical reactions that occur initially between the cement and water and subsequent reactions that continue during the hardening of the concrete. This also includes the interaction involving chemical admixtures and supplementary cementing materials and effects they have on the plastic and hardened states of the concrete. In this study, we synthesized new polymeric additives based on polar group grafted polar polymers to increase performance and plasticization of cement. The main chain was choosen Polyethylene Glycol 6000 and polyitaconic acid. The characterization of synthesized polymeric additives was done according to TS EN 480-1 standard. The results showed that functionalized PIA samples showed better effects on mortar than those of functionalized PEG 6000 samples.Yüksek LisansM.Sc

Study of the morphological and thermal properties of polystyrene nanocomposites based on modified halloysite nanotubes with styrene-maleic anhydride copolymers

In this study, the melt blending method was used to prepare the polystyrene/halloysite nanotubes (PS/HNTs) nanocomposites instead of in-situ bulk polymerization of styrene monomer in the presence of HNTs. Surface modification of HNTs with styrene-maleic anhydride copolymers (SMA) was performed in THF medium to improve the HNTs distribution and compatibility in the PS matrix. PS/HNTs nanocomposites were prepared in a twin-screw micro compounder containing 5, 10, and 15 wt.% of nanoclays. The influences of the surface modification of HNTs on the properties of the nanocomposites were studied by XRD, SEM, DSC, TGA, and tensile test. The SEM images showed that the modified HNTs samples were uniformly distributed in the PS matrix compared to the pristine HNTs. The thermal stability of nanocomposites was also improved by increasing of modified HNTs content. Consequently, the surface modification increased the dispersion of HNTs in the PS nanocomposites prepared by melt blending method

The manufacture of organic carbonate-poly(methyl ethylacrylate) nanowebs with thermal buffering effect

In this study, novel nanowebs provided with thermal buffering properties were developed via coaxial electro-spinning. Environmental friendly and nontoxic dialkyl and dialkenyl carbonates (DACs), namely, didecyl carbonate, didodecyl carbonate, ditetradecyl carbonate, dihexadecyl carbonate, dioctadecyl carbonate and dioleyl carbonate were synthesized from their fatty alcohols based on carbonate interchange reaction. Then the DAC-PMEA nanowebs were produced using 10-50 w% DAC in 3:1 chloroform-ethanol solution as core and 15 w% poly(methyl ethylacrylate) (PMEA)in ethanol as shell by coaxial electrospinning. The SEM images of the nanowebs presented randomly oriented, ultrafine fibers identified with smooth surfaces, continuous and cylindrical shapes. The nanowebs were able to provide considerable enthalpies (40-100 J g(-1)) during their repeated phase changes, up to hundred heating-cooling cycles, corresponding to 52-92% efficiencies obtained from electrospinning. These shape stabilized, lightweight DAC-PMEA nanowebs showed a significant potential for the dynamic thermal insulation applications across various industries, especially for the protection of temperature sensitive materials

Wet chemical method for highly flexible and conductive fabrics for smart textile applications

This study reports the preparation of highly flexible and conductive fabrics containing zinc oxide (ZnO), silver nanowires (AgNW) and graphene flakes (GFs) by simple vacuum filtration. The ZnO particles prepared with sol-gel method in large sizes with flower-like shape were used as filler and became the first layer to be coated on the fabric surface. These particles covered the gaps at the junction of the fabric fibers, providing a suitable area for the deposition of subsequent layers of AgNW and GFs. The structural, morphological and conductivity properties of the prepared conductive fabric were investigated by XRD, optical and electron microscopy as well as four-point probe conductivity measurement. The optical images showed that a continuous conductive network was obtained that allowed electron transport across the fabric surface. The fabric was found to have a remarkably low sheet resistance of an average of 1.5 Ω/sq. This result displays that promising candidates suitable for conductive textile applications can be prepared by simple vacuum filtration method

Low temperature chemical treatment of graphene films made by double self-assembly process to improve sheet resistance

In this study, a low temperature hydro iodic acid (HI) vapor treatment of the self-assembled graphene films has been developed, and the electrical, optical, structural and morphological properties were investigated by four point probe, UV-Visible spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). Mono-, doubleand triple-layer of graphene flakes were deposited on glass substrates by using the Double Self-Assembly (DSA) process. The self-assembled graphene films were treated with HI vapors at 40 degrees C for different time intervals between 1 and 24 h. In addition, graphene deposition and HI-vapor treatment (at 40 degrees C for 1 h) was enforced three times to the same substrate. The optical transparency values of the self-assembled mono- (MGFs), double- (DGFs) and triple-layer graphene flakes (TGFs) were measured as 91, 85 and 80%, respectively (values at 550 nm). Due to the HI-vapor treatment, the sheet resistance of MGFs significantly reduced from 1.1 x 10(7) Omega omega square(-1) to 2.9 x 10(4) omega square(-1), the transparency of the graphene films slightly reduced by 2-5%, the I-D/I-G ratio of the DGFs decreased from 1.01 to 0.81, while the I-2D/I-G ratio increased from 0.43 to 0.48 in the Raman spectrum. Thanks to its impressive reducing effect on sheet resistance, HI-vapor treatment can be a suitable method to improve the conductivity of low-cost large area graphene films

A handbook for graphitic carbon nitrides: revisiting the thermal synthesis and characterization towards experimental standardization

Graphitic carbon nitrides (g-C3N4s) have continued to attract attention as metal-free, low-cost semiconductor catalysts. Herein, a systematic synthesis and characterization of g-C3N4s prepared using four conventional precursors (urea (U), dicyandiamide (DCDA), semicarbazide hydrochloride (SC-HCl), and thiosemicarbazide (TSC)) and an unexplored one (thiosemicarbazide hydrochloride (TSC-HCl)) is presented. Equal synthesis conditions (e.g. heating and cooling rates, temperature, atmosphere, reactor type/volume etc) mitigated the experimental error, offering fair comparability for a library of g-C3N4s. The highest g-C3N4 amount per mole of the precursor was obtained for D-C3N4 (∼37.85 g), while the lowest was for S-C3N4 (∼0.78 g). HCl addition to TSC increased the g-C3N4 production yield (∼5-fold) and the oxygen content (T-C3N4∼3.17% versus TCl-C3N4∼3.80%); however, it had a negligible effect on the level of sulphur doping (T-C3N4∼0.52% versus TCl-C3N4∼0.45%). S-C3N4 was the darkest in color (reddish brown), and the band gap energies were S-C3N4(2.00 eV) < T-C3N4(2.74 eV) < TCl-C3N4(2.83 eV) ≤ D-C3N4(2.84 eV) < U-C3N4(2.97 eV). The experimentally derived conduction band position of S-C3N4(−0.01 eV) was closer to the Fermi energy level than the others, attributable to high oxygen atom doping (∼5.11%). S-C3N4 displayed the smallest crystallite size (∼3.599 nm by XRD) but the largest interlayer distance (∼0.3269 nm). Furthermore, BET surface areas were 138.52 (U-C3N4), 22.24 (D-C3N4), 18.63 (T-C3N4), 10.51 (TCl-C3N4), and 9.31 m2 g−1 (S-C3N4). For the first time, this comprehensive handbook gives a glimpse of a researcher planning g-C3N4-based research. It also introduces a novel oxygen-sulphur co-doped g-C3N4 (TCl-C3N4) as a new halogen-free catalyst with a relatively high production yield per mole of precursor (∼24.09 g)

Development of heat storing poly(acrylonitrile) nanofibers by coaxial electrospinning

New thermal energy storage materials were developed as poly(acrylonitrile) (PAN) nanofibers with encapsulated phase change materials (PCMs). Sixteen samples composed of PAN shells and PEG or PEGME cores, and one control sample composed of only a PAN shell, were manufactured by coaxial electrospinning. SEM images revealed the formation of randomly distributed, distinct nanofibers with smooth surfaces and cylindrical shapes along their lengths. FTIR results confirmed bicomponent nanofiber structures and TGA results demonstrated their thermal stabilities. Phase change performances of nanofibers were repeatedly examined by DSC analyzes; heating enthalpies ranged from 38 to 133 J g(-1) and from 29 to 60 J g(-1) for PAN-PEGs and PAN-PEGME samples, respectively, corresponding to good encapsulation efficiencies. These remarkable thermal energy storages were achieved at different melting temperatures (- 1 to 60 degrees C). Textile based sandwich structures containing three different types of PAN-PCM nanowebs demonstrated enhanced thermal properties and buffering function against temperature changes in surrounding

Non-destructive covalent surface alkylation of graphitic carbon nitride for enhanced photocatalytic dye degradation in water

Graphitic carbon nitride (g-CN) is a promising material for various applications due to its unique electronic, optical, and photocatalytic properties, tunable by surface modifications. Herein, a novel and straightforward approach to the covalent addition of low molecular weight polyethylene glycol (PEG550) to g-CNs surface following non-destructive chemistry benefiting from simultaneous activation of hydroxyl and free-amine surface groups by a weak base, potassium carbonate, is for the first time described. The resulting g-CN-PEG550 exhibits almost two-fold enhanced water solubility due to 1 PEG550 chain addition for every ∼ 128 g-CN atoms, detected by thermogravimetric analysis. Complementary X-ray photoelectron spectroscopy elemental analysis of the isolated g-CN-PEG550 displays an increased C─O chemical environment attributed to the covalent addition of carbon- and oxygen-rich PEG550 to the g-CN surface. The g-CN-PEG550 photocatalyst performs 2.5-fold better in degrading rhodamine B due to its enhanced light absorption, improved water-dispersibility, and the efficient separation of photogenerated electron-hole pairs compared to the as-prepared g-CN. The study underscores the potential use of covalently PEGylated oxygen-rich g-CNs in photocatalytic applications

Ethanol sensing with pure and boric acid doped eectrospun CuInS2 nanofibers in the presence of relative humidity

The influence of boric acid doping on ethanol vapor sensing performance of electrospun copper indium disulfide (CuInS2) nanofibers in the presence of various levels of relative humidity was examined for the first time. Pure and boric doped CuInS2 nanofibers are prepared through electrospinning method and characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy and Thermogravimetric analysis techniques. It was found that not only the ethanol sensing performance but also base line current of the CuInS2 nanofiber based sensors are greatly influenced by the boric acid doping level. Maximum sensitivity was obtained with pure CuInS2 under humid conditions. Kinetic studies indicated that ethanol vapor adsorption kinetics strongly depend on level of the relative humidity and the ethanol concentration