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    The effect of graphene nanoplatelets on technical properties of micro- and nano-sized TiO2 matrix: a comparative research study on electrical and optical characteristics
    (Springer, 2020) Güler, Ömer; Ayhan, Hakan; Başgöz, Öyküm; Başgöz, Öyküm; Yavuz, Çağdaş; Albayrak, Muhammet Gökhan; Evin, Ertan; Safa, Hasan; Ibrahim S. Yahia
    In this study, titanium dioxide (TiO2)-based graphene nanoplatelets (GNPs)-reinforced composite materials were produced and the electrical and optical properties of the composite materials were investigated. Graphene, which was used as a reinforcing material, was produced by using liquid-phase exfoliation method. While the TiO2 used as matrix material was commercially available for the first group of samples, it was produced by using the sol–gel method for the second group of the samples. Different rates of graphene were added to the TiO2 powders which were commercially available and produced by using sol–gel method. GNPs used as a reinforcing material were subjected to TEM analysis. The resulting composite materials were structurally examined in SEM and XRD. Then, the changes in electrical conductivity of these composites under the impact of temperature were measured. UV–Vis spectrometers of the samples were taken and their optical properties were determined. When temperature-based electrical examination of the produced composite materials was performed, an increase was observed on the electrical conductivity values in both groups of samples as a result of addition of the reinforcing element. In addition, TiO2-containing composites produced by using sol–gel method had lower electrical conductivity comparing with commercially purchased TiO2-containing composites especially at high temperatures. In the optical measurements, it was observed that there was an increase in the optical bandgap energy range values with GNPs reinforcement but a decrease in the reflectance values.
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    The synergistic effect of CNTs-polymeric surfactant on the properties of concrete nanocomposites: Comparative study
    (Sage Publications Ltd, 2021) Guler, Omer; Cacim, Nazli N.; Evin, Ertan; Yahia, Ibrahim S.
    Carbon nanotubes (CNTs) have been used as reinforcing material for many different matrices. There are many studies in the literature reporting that reinforcement of CNTs into concrete matrix improved the properties of the concrete. In this study, first unmodified CNTs were reinforced to concrete and it was seen that there were partial decreases in strength despite the increasing rate of CNTs. Thereon, the surfaces of CNTs to be used as reinforcing material were modified with water-soluble surfactants (Polyvinyl alcohol-PVA, Polyvinylpyrrolidone-PVP, Poly (ethylene glycol)-PEG, Dodecylamine-DDA) and reinforced with concrete. In previous studies, many different surfactants were tried to functionalise the surfaces of CNTs. However, in this study, water-soluble polymeric surfactants were preferred without the need for an additional process in order to modify the surfaces of CNTs. In addition, the effect of the surfactants used on the mechanical properties of concrete was examined comparatively. Although the amount of CNTs reinforcement is very low like 0.05 wt%, the increase in strength was seen to be above 60%. The highest strength values were obtained in the sample in which PVA was used as surfactant. Through the surfactants used, bundles of CNTs were fully opened and distributed homogeneously into the concrete matrix, and all of the CNTs were embedded into the matrix by getting wet by the matrix. In the real application, it will be possible to use new generation concretes with higher strength and lighter weight by providing the ease of reinforcing CNTs to the concrete matrix.