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Improving the mechanical properties of bitumen is an important goal for road pavements design. For this reason, new compounds are now being sought for testing as bitumen modifiers.In this work, the authors studied the effect that two different chars have on two 50/70 bitumens with different chemical and physical characteristics. A complete morphological, surface and bulk characterization of the two additives was carried out. In addition, rheology, Nuclear Magnetic Resonance (NMR) relaxometry and atomic force microscopy were used to analyze the effect that the two additives exert on the properties of the bitumens. According to the results, the char sample with high porosity could be used as a modifier of mechanical properties, while no rejuvenation effects were observed for either of the two additives tested. In addition, the two additives do not give rise to segregation phenomena.

Road pavement characteristics can be improved by modifying bitumens through addition of fine particles. To avoid environmental issues, attention is recently being paid to bio-materials. In this study, a 50/70 bitumen was modified through the addition of char obtained from the pyrolysis of waste tires. Char addition causes an increase in transition (gel to sol) temperature of up to 4 °C and an increase in rigidity under working conditions (50 °C) of up to about one order of magnitude. The effect of the gas type flowing under the pyrolysis process (CO2, N2 and CO2 + N2) on the mechanical characteristics of the bitumen was also investigated. More marked effects on the rheological performances were found if char coming from pyrolysis under CO2 was used (the gel-to-sol transition temperature is increased by about 4.5 °C) compared to that coming from pyrolysis under N2 (gel-to-sol transition temperature is increased by about 3 °C). The effect is at a maximum for char from CO2 at 3% wt/wt, whereas regarding char from N, a lesser effect is seen with a more uniform (flat) effect as a function of char% and with an increase in gel-to-sol transition temperature of about 3 °C. Coherently, char obtained from pyrolysis under CO2 was found to possess a higher surface area constituted by smaller particles than that coming from pyrolysis under N2. In fact, the BET-specific surface passes 79 m2/g for N2-char to 174 m2/g for CO2-char and the micropore volume fraction increases from 2 to 9. The observed differences can be attributed to the oxidizing environment (CO2) that is more aggressive and reactive in the synthesis phase compared to an inert environment (N2). Char also showed an anti-aging effect, hindering the increase in rigidity typically associated with the aging process. This effect was explained in terms of the compatibility of char with bitumen’s organic nature, and presumably its more effective hosting in a bituminous structure, which is presumably higher when char is produced under CO2 rather than N2. This study quantitatively indicates how a residue derived from the pyrolysis of a waste material can be efficiently re-used to increase the mechanical characteristics of bitumen, accomplishing the recent circular-based needs for environmental protection.

We report on successful refractive index profiling of commercially available step-index and in-house made graded-index multimode specialty optical fibers by means of X-ray computed microtomography. Our results demonstrate that the latter is an advantageous technique for characterizing large core optical fibers, which allows for retrieving information about the refractive index at optical frequencies by exploiting the absorption coefficient of X-rays.

Vacancies in atomically thin molybdenum disulphide play an essential role in controlling its optical and electronic properties, which are crucial for applications in sensorics, catalysis or electronics. For this reason, defect engineering employing thiol-terminated molecules is used to heal and/or functionalise defective nanosheets. In this work, chemical vapour deposition-grown MoS _2 with different defect densities was functionalised with three molecules: 4-aminothiophenol (ATP), biphenyl-4-thiol (BPT) and 4-nitrothiophenol (NTP). The molecules’ efficacy in functionalising MoS _2 was probed by x-ray photoelectron, Raman and photoluminescence (PL) spectroscopy. The results show that exposing a defective single layer of MoS _2 to either ATP, BPT or NTP molecules heals the defects, however the chemical structure of these molecules affects the optical response and only for BPT the PL intensity increases.

Road pavement characteristics can be improved by modifying bitumens through addition of fine particles. To avoid environmental issues, attention is recently being paid to bio-materials. In this study, a 50/70 bitumen was modified through the addition of char obtained from the pyrolysis of waste tires. Char addition causes an increase in transition (gel to sol) temperature of up to 4 °C and an increase in rigidity under working conditions (50 °C) of up to about one order of magnitude. The effect of the gas type flowing under the pyrolysis process (CO2, N2 and CO2 + N2) on the mechanical characteristics of the bitumen was also investigated. More marked effects on the rheological performances were found if char coming from pyrolysis under CO2 was used (the gel-to-sol transition temperature is increased by about 4.5 °C) compared to that coming from pyrolysis under N2 (gel-to-sol transition temperature is increased by about 3 °C). The effect is at a maximum for char from CO2 at 3% wt/wt, whereas regarding char from N, a lesser effect is seen with a more uniform (flat) effect as a function of char% and with an increase in gel-to-sol transition temperature of about 3 °C. Coherently, char obtained from pyrolysis under CO2 was found to possess a higher surface area constituted by smaller particles than that coming from pyrolysis under N2. In fact, the BET-specific surface passes 79 m2/g for N2-char to 174 m2/g for CO2-char and the micropore volume fraction increases from 2 to 9. The observed differences can be attributed to the oxidizing environment (CO2) that is more aggressive and reactive in the synthesis phase compared to an inert environment (N2). Char also showed an anti-aging effect, hindering the increase in rigidity typically associated with the aging process. This effect was explained in terms of the compatibility of char with bitumen's organic nature, and presumably its more effective hosting in a bituminous structure, which is presumably higher when char is produced under CO2 rather than N2. This study quantitatively indicates how a residue derived from the pyrolysis of a waste material can be efficiently re-used to increase the mechanical characteristics of bitumen, accomplishing the recent circular-based needs for environmental protection. [ABSTRACT FROM AUTHOR]

In the field of structural strengthening, the need to replace common composite materials with sustainable ones has been developing in the last decade. Sustainable composite materials, such as a natural fiber-reinforced cementitious matrix (NFRCM), are both eco-friendly regarding the reinforcing fibers and the matrix. For the purpose of this work, in the first part, a type of natural fiber made with basalt was investigated. In particular, various matrices with different compositions and mechanical properties were considered during the laboratory design and production of composite materials. One inorganic and two organic matrices were studied, classifying and analyzing them in terms of compressive strength, flexural strength, and tensile strength. After that, basalt fibers and NFRCM specimens were characterized under tensile stress using the different type of matrix mentioned previously. All the matrices were made with the same mortar and differ because of the resin component. Specifically, the first was the only matrix made of an inorganic resin. The second and the third shared the same resin but had different resin mortar weight ratios. Only the second type had a nonnegligible water content. In particular, tests were conducted on five basalt strips, nine prisms subjected to three-point bending and compression tests (three for each type of matrix) and 15 basalt FRCM composites samples (also with five for each type of matrix). The comparison of the results obtained on the analyzed composites are in accordance with the results found in literature. The second part of the present work consists of identifying through x-ray microtomography a correlation between the voids of the NFRCM and the adhesion between matrix and fiber. In fact, an x-ray microtomography was carried out to analyze the adhesion status between the cementitious matrix and the basalt fibers tested during the experimental campaign. The x-ray microtomography imaging was used to obtain a nondestructive two-dimensional (2D) and three-dimensional (3D) characterization of the specimens and to detect cracks and voids. A complete set of 2D projections was acquired and a 3D map of the x-ray absorption in the volume was mathematically reconstructed. The 3D map permitted the precise position of the voids and damage in the different specimens analyzed. In particular, we show that the percentage of fiber voids in the sample made with the inorganic resin was half that of the sample made with the organic resin, i.e., 1.8%±0.5% and 3.5%±0.5% respectively. The number of holes in the matrix of these two samples was comparable. The sample whose resin contains water, on the other hand, turned out to be considerably different. Specifically, at variance with the former samples, we found that the percentage of voids in the matrix of the latter was higher than 3%, Additionally, by examining the anisotropy of the voids in the basalt fibers, it was possible to show the relationship between mechanical stress and the presence of voids in the fibers. According to our findings, the percentage of voids in the fibers parallel to the tensile tension in the inorganic sample was about twice that of the fibers shifted perpendicularly to the tensile stress, i.e., 0.60%±0.03% and 0.34%±0.01% respectively: the sample stress can only explain this difference. [ABSTRACT FROM AUTHOR]

Pinecones, a common biomass waste, has an interesting composition in terms of cellulose and lignine content that makes them excellent precursors in various activated carbon production processes. The synthesized, nanostructured, activated carbon materials show textural properties, a high specific surface area, and a large volume of micropores, which are all features that make them suitable for various applications ranging from the purification of water to energy storage. Amongst them, a very interesting application is hydrogen storage. For this purpose, activated carbon from pinecones were prepared using chemical activation with different KOH/precursor ratios, and their hydrogen adsorption capacity was evaluated at liquid nitrogen temperatures (77 K) at pressures of up to 80 bar using a Sievert’s type volumetric apparatus. Regarding the comprehensive characterization of the samples’ textural properties, the measurement of the surface area was carried out using the Brunauer–Emmett–Teller method, the chemical composition was investigated using wavelength-dispersive spectrometry, and the topography and long-range order was estimated using scanning electron microscopy and X-ray diffraction, respectively. The hydrogen adsorption properties of the activated carbon samples were measured and then fitted using the Langmuir/ Töth isotherm model to estimate the adsorption capacity at higher pressures. The results showed that chemical activation induced the formation of an optimal pore size distribution for hydrogen adsorption centered at about 0.5 nm and the proportion of micropore volume was higher than 50%, which resulted in an adsorption capacity of 5.5 wt% at 77 K and 80 bar; this was an increase of as much as 150% relative to the one predicted by the Chahine rule.

The 3:2 Charge Transfer (CT) co-crystal (Perylene)3(TCNQF1)2 is grown by the Physical Vapor Transport (PVT) method, and characterized structurally and spectroscopically. Infrared analysis of the charge sensitive modes reveals a low degree of charge transfer (less than 0.1) between donor and acceptor molecules. The crystal is isostructural to the other 3:2 CT crystals formed by Perylene with TCNQF2 and TCNQF4, whereas such stoichiometry and packing is not known for the CT crystals with non-fluorinated TCNQ. The analysis of the isostructural family of 3:2 Perylene−TCNQFx (x = 1,2,4) co-crystal put in evidence the role of weak F…HC bonding in stabilizing this type of structure

We propose the use of solid solutions for the modulation of the kinetics in [2 + 2] photocycloaddition. Solid solutions with general formula [1H]BrxCl1−x (1 = 4-amino-cinnamic acid; 0 < x < 1) were prepared via mechanochemical methods, structurally characterized, and found to undergo a single-crystal-to-single-crystal [2 + 2] photodimerization. The effect of the solid solution composition on the kinetics was successfully investigated via a combination of FTIR and principal component analysis (PCA), and the results were compared with those obtained for the parent materials [1H]Cl and [1H]Br. All systems follow the same nearly first-order law, and the overall reaction kinetics is influenced by a subtle interplay of structural and electronic factors as well as other processes regulating the formation and lifetime of the reacting excimer. [ABSTRACT FROM AUTHOR]

A careful analysis of the vibrational spectra of two isostructural charge transfer systems with potential applications in optoelectronics, (perylene)3‐(TCNQF4)2, and (perylene)3‐(TCNQF2)2, highlights the presence of three strong infrared bands, polarized along the (perylene‐TCNQFx‐perylene) trimeric units present in the crystal. These bands are recognized as due to the Holstein, or electron–molecular vibration (e–mv) interaction. Use of appropriate modeling, based on the analysis of the frequency shifts due to the e–mv coupling, allows to extract the relevant Holstein coupling constants for the HOMO of the perylene molecule. The so‐obtained experimental values agree very well with density functional calculations, thus validating the results. The perylene relaxation energy, or small polaron binding energy, is about 70 meV, of the same order of magnitude as that of pentacene. [ABSTRACT FROM AUTHOR]

The computational protocol we have developed for the calculation of local (Holstein) and non-local (Peierls) carrier-phonon coupling in molecular organic semiconductors is applied to both the low temperature and high temperature bulk crystalline phases of pentacene. The electronic structure is calculated by the semimpirical INDO/S (Intermediate Neglect of Differential Overlap with Spectroscopic parametrization) method. In the phonon description, the rigid molecule approximation is removed, allowing mixing of low-frequency intra-molecular modes with inter-molecular (lattice) phonons. A clear distinction remains between the low-frequency phonons, which essentially modulate the transfer integral from a molecule to another (Peierls coupling), and the high-frequency intra-molecular phonons, which modulate the on-site energy (Holstein coupling). The results of calculation agree well with the values extracted from experiment. The comparison with similar calculations made for rubrene allows us to discuss the implications for the current models of mobility. [ABSTRACT FROM AUTHOR]

The high-pressure properties of the molecular crystal para-diiodobenzene are investigated by combining optical absorption, reflectance, and Raman experiments with Car-Parrinello simulations. The optical absorption edge exhibits a large red shift from 4 eV at ambient conditions to about 2 eV near 30 GPa.

In situ functionalized, with different organically groups, mesoporous matrices were generated, starting from silica tetra-alcoxide and functionalized tri- or di-alkoxides, (triethoxyvinylsilan, diethoxy(methyl)vinylsilane and methyltriethoxysilane) mixtures, via sol-gel synthesis. Mesoporous silica matrices have been prepared with the purpose of tailor and optimize their performances as gas storage materials. In this concern, it was designed different experiments to study how the synthesis variables influence the matrix morpho textural properties, being aware that this kind of properties play an important role in the gas adsorption-desorption processes. In order to prepare spherical particles, ammonia was used as catalyst. Eventually, in order to tailor the pore shape and size and implicitly the specific surface area, hexadecyltrimethyl ammonium bromide as directing agent was added, and the molar ratios of organically functionalized precursors/TEOS, were varied. The H2, CH4 and CO2 adsorption properties of prepared functionalized mesoporous silica with different compositions have been studied. In the used experimental conditions, data analysis permits to conclude that the methyl functionalized sample, according to its structural parameters, at 77 K and elevate pressure it showed the best performances concerning the adsorption capacity toward H2 and CO2. CH4 molecules. Toward CH4 molecules, in particular, the analysis performed at room temperature point out that the vinyl- functionalized samples have an appreciable affinity toward this gas specimen. [ABSTRACT FROM AUTHOR]

We present the optical principle of a white-pupil collimator made up of two mirrors with unequal focal lengths. Analytic formulas for third-order aberrations are derived and compared with the results of ray-tracing experiments. It is shown that the image quality is good if the second mirror has a suitable conic coefficient and the F ratio is not too small. Furthermore, third-order coma and astigmatism can be zeroed simultaneously if the angles are also appropriately selected. When implemented in high-resolution echelle spectrographs, this design permits smaller cross dispersers and cameras, with considerable savings in cost. [C] 2000 Optical Society of America OCIS codes: 120.6200, 220.1000, 120.1680.