Enhanced exfoliation technique for the separation of graphene nanosheets

Graphene sheets are carbon-based materials which combine exceptional electron conductivity, mechanical strength and optical transparency. Graphene nanosheets were fabricated by an enhanced, safer and mild technique in a shortened processing time. Samples were characterized by SEM, XRD, TGA, AFM and Raman Spectroscopy

Interrelationships of pressure-dependent hole fraction and elongational viscosity in polymer melts

The elongational flow behavior of polyethylene, polypropylene, polystyrene, poly(methyl methacrylate), and polycarbonate, temperatures from 70 to 290∘ C and pressures up to 70 MPa, is examined with the Yahsi-Dinc-Tav (YDT) model and its particular case known as the Cross model. The viscosity data employed in the range of 3-405 s-1 elongational rates were acquired from the literature at ambient and elevated pressures. The predictions and the fitting results of the proposed YDT model with the same measurement data are compared with the Cross model. The average absolute deviations of the viscosities predicted by the YDT model range from 0.54% to 9.44% at ambient and 1.95% to 6.28% at high pressures. Additionally, the linear formulations derived from the YDT model are employed to relate the viscosity with temperature and hole fraction (“thermooccupancy” function) at zero level of elongational rate and constant elongational rate along with constant elongational stress. The effects of the four viscosity parameters (such as transmission and activation energy coefficients in these equations) on the elongational viscosity are analyzed in detail and some conclusions on the structural differences for the polymers are discussed. © 2019 Fatma Sahin-Dinc et al

Graphene manufacture and utilization

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tullelike translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp2 domains of graphene nanosheets obtained after the reduction of graphite oxide

Brain Breaks Physical Activity Solutions® in higher education: Randomized controlled trial among Turkish university student

A substantial volume of empirical evidence exists regarding the positive effects of technology-supported physical activity (PA) solutions in school children. However, a lack of potential impact of these solutions in higher education settings exists. This study aimed to examine the effects of Brain Breaks PA Solutions® on university students’ attitudes toward PA. This study used a pre-test and post-test with a quasi-experimental design and convenience sampling. Students (n = 521) from seven different faculties of a public university in the Cappadocia region of Turkey volunteered as study participants and were randomly assigned to either experimental (n = 263) or control (n = 258) groups. During a 3-month intervention, the experimental groups received Brain Breaks PA Solutions® videos. Student attitudes toward PA were measured using the attitudes toward PA Scale (APAS) before and after the intervention. Repeated measures analysis of variance indicates a time interaction effect for PA benefits. Time-by-group interaction effects with varying effect sizes were found for most APAS variables with the greatest gain noted in the experimental groups for fun, followed by learning from the videos, and self-efficacy (P < 0.05). This study provides evidence that technology-supported PA programs in higher education settings positively impact students’ attitudes toward PA

Chemical composition and oxidation study of nitrogen doped carbon nanotubes

In this work, carbon nanotubes (CNTs) and nitrogen doped carbon nanotubes (N-CNTs) were synthesized by aerosol chemical vapour deposition and the synthesis parameters such as temperature, catalyst concentration, precursor concentration, gas flow rate and reaction time were studied. N incorporation was extensively investigated on the basis of N bonding configurations detected by X-ray photoelectron spectroscopy (XPS), N concentration distribution measured by electron energy loss spectroscopy (EELS) and N spatial distribution by aberration corrected scanning transmission electron microscopy coupled with EELS (STEM-EELS). Pyridinic, graphitic, gaseous and N-oxide configurations were detected. EELS revealed N concentration differed from nanotube to nanotube within a given sample and also differed from region to region on a given nanotube. N is mostly concentrated regions of high curvature such as dome of repetitive compartments occurring within the inner channel of nanotubes. N was also found towards the innermost graphitic shells. The effects of N incorporation on nanotube outer and inner diameter distributions, wall thickness, morphology types, and morphology distributions are demonstrated. Correlations were found between nanotube morphology and chemical composition. Gaseous N tends to occur in thin-walled N-CNTs with large inner diameters and to be found in hollow and incomplete compartments morphologies. Si occurrence was also detected in CNT and N-CNT samples. Oxidation resistance of CNTs and N-CNTs synthesized from a variety of C/N ratios were studied by thermogravimetric analysis. Undoped CNTs and N-CNTs were classified into three groups of oxidation in terms of the number of oxidation steps they followed. CNTs showed single step oxidation whereas N-CNTs showed two or three steps, indicating the non-uniform chemical composition of N-CNTs. This might result from the N concentration differing from nanotube to nanotube within a given sample and the N concentration differing from region to region in a given nanotube. Partially oxidised CNTs and N-CNTs were characterised by aberration corrected STEM-EELS to map their elemental compositions and understand the chemical changes they undergo during oxidation, which revealed that oxidation starts at specific sites in CNTs and N-CNTs.</p

Chemical composition and oxidation study of nitrogen doped carbon nanotubes

In this work, carbon nanotubes (CNTs) and nitrogen doped carbon nanotubes (N-CNTs) were synthesized by aerosol chemical vapour deposition and the synthesis parameters such as temperature, catalyst concentration, precursor concentration, gas flow rate and reaction time were studied. N incorporation was extensively investigated on the basis of N bonding configurations detected by X-ray photoelectron spectroscopy (XPS), N concentration distribution measured by electron energy loss spectroscopy (EELS) and N spatial distribution by aberration corrected scanning transmission electron microscopy coupled with EELS (STEM-EELS). Pyridinic, graphitic, gaseous and N-oxide configurations were detected. EELS revealed N concentration differed from nanotube to nanotube within a given sample and also differed from region to region on a given nanotube. N is mostly concentrated regions of high curvature such as dome of repetitive compartments occurring within the inner channel of nanotubes. N was also found towards the innermost graphitic shells. The effects of N incorporation on nanotube outer and inner diameter distributions, wall thickness, morphology types, and morphology distributions are demonstrated. Correlations were found between nanotube morphology and chemical composition. Gaseous N tends to occur in thin-walled N-CNTs with large inner diameters and to be found in hollow and incomplete compartments morphologies. Si occurrence was also detected in CNT and N-CNT samples. Oxidation resistance of CNTs and N-CNTs synthesized from a variety of C/N ratios were studied by thermogravimetric analysis. Undoped CNTs and N-CNTs were classified into three groups of oxidation in terms of the number of oxidation steps they followed. CNTs showed single step oxidation whereas N-CNTs showed two or three steps, indicating the non-uniform chemical composition of N-CNTs. This might result from the N concentration differing from nanotube to nanotube within a given sample and the N concentration differing from region to region in a given nanotube. Partially oxidised CNTs and N-CNTs were characterised by aberration corrected STEM-EELS to map their elemental compositions and understand the chemical changes they undergo during oxidation, which revealed that oxidation starts at specific sites in CNTs and N-CNTs.</p