Solvent-dependent termination, size and stability in polyynes synthesis by laser ablation in liquids

In recent years there has been a growing interest in sp-carbon chains as possible novel nanostructures. An example of sp-carbon chains are the so-called polyynes, characterized by the alternation of single and triple bonds that can be synthesized by pulsed laser ablation in liquid (PLAL) of a graphite target. In this work, by exploiting different solvents in the PLAL process, e.g. water, acetonitrile, methanol, ethanol, and isopropanol, we systematically investigate the solvent role in polyyne formation and stability. The presence of methyland cyano-groups in the solutions influences the termination of polyynes, allowing to detect, in addition to hydrogen-capped polyynes up to HC22H, methyl-capped polyynes up to 18 carbon atoms (i.e. HCnCH3) and cyanopolyynes up to HC12CN. The assignment of each species was done by UV-Vis spectroscopy and supported by density functional theory simulations of vibronic spectra. In addition, surface-enhanced Raman spectroscopy allowed to observe differences, due to different terminations (hydrogen, methyl-and cyano group), in the shape and positions of the characteristic Raman bands of the size-selected polyynes. The evolution in time of each polyyne has been investigated evaluating the chromatographic peak area, and the effect of size, terminations and solvents on polyynes stability has been individuated.Comment: 13 pages, 5 figures. Supporting Information of this article is available in the end of this manuscrip

Analysis of Nb3_{3}Sn Rutherford cable production and strand deformations

The development of cutting-edge 11-12 T superconducting magnets made from Nb$_{3}$Sn technology is one of the major milestones for the upgrade of the Large Hadron Collider at CERN. The upgrade, called High Luminosity LHC Project, was planned in order to reach higher luminosity and discover new particles. Replacing the NbTi superconductor with the Nb$_{3}$Sn makes it possible to reach a practical operating magnetic field limit of up to 16 T. The superconducting coils are formed by Nb$_{3}$Sn Rutherford cables with a trapezoidal cross section and composed of 40 strands. Since the superconducting phase of Nb$_{3}$Sn is very brittle and it is reached after a thermal cycle, the Nb$_{3}$Sn Rutherford cable needs to be wound in a coil before the thermal treatment. The cabling process is a delicate step in the production of high performing cables that need different systems to control their quality. This work aims to provide practical tools to analyze the Nb$_{3}$Sn Rutherford cable production and the strands deformations due to the high aspect ratio of the Rutherford cable. Thanks to these tools it was possible to monitor the fluctuations of the mechanical tensions of the strands during cabling, localize the manufacturing defects and find the critical mechanical distortions inside the strands which cause degradation in the electrical performances. The results of the fluctuations in mechanical tensions are compared to the size variation of the lateral facets of the cable and the data related to the number of critical deformations are compared to the degradation of the electrical performances; the comparisons were performed in order to investigate a possible specific correlation. However, further measurements are foreseen to confirm the results

Pulsed laser ablation in liquid of sp-carbon chains: status and recent advances

This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid. In recent years, pulsed laser ablation in liquid (PLAL) has been widely employed for polyynes synthesis thanks to its flexibility with varying laser parameters, solvents, and targets. This allows the control of sp-carbon chains properties as yield, length, termination and stability. Although many reviews related to PLAL have been published, a comprehensive work reporting the current status and advances related to the synthesis of sp-carbon chains by PLAL is still missing. Here we first review the principle of PLAL and the mechanisms of formation of sp-carbon chains. Then we discuss the role of laser fluence (i.e. energy density), solvent, and target for sp-carbon chains synthesis. Lastly, we report the progress related to the prolonged stability of sp-carbon chains by PLAL encapsulated in polymeric matrices. This review will be a helpful guide for researchers interested in synthesizing sp-carbon chains by PLAL

Characterization of Nb3_3Sn Rutherford Cable Degradation Due to Strands Cross-Over

The quadrupole and dipole magnets for the LHC High Luminos-ity (HL-LHC) upgrade will be based on Nb$_{3}$Sn Rutherford ca-bles that operate at 1.9 K and experience magnetic fields larger than 12 T. The Nb$_{3}$Sn Rutherford cables are assembled via by a planetary machine able to produce the trapezoidal geometry with the required mechanical tolerances (about $\pm$ 0.01 mm) and low critical current degradation (<5%). One of the critical as-pects of Rutherford cable production is the control of the tension that is applied to each strand of the cable during the cabling process. If the strands are too loose during cabling, strands cross-over can be induced with a consequent locally high me-chanical deformation and potential performance degradation. In this paper the processes implemented at CERN for preventing and detecting strands cross-over during cables production are presented. The effect of cross-over on the electrical performance of a RRP - Rutherford cable is also reported and discussed.The quadrupole and dipole magnets for the LHC high luminosity upgrade will be based on Nb3Sn Rutherford cables that operate at 1.9 K and experience magnetic fields larger than 12 T. The Nb3Sn Rutherford cables are assembled via a planetary machine able to produce the trapezoidal geometry with the required mechanical tolerances (about ±0.01 mm) and low critical current degradation (<;5%). One of the critical aspects of Rutherford cable production is the control of the tension that is applied to each strand of the cable during the cabling process. If the strands are too loose during cabling, strands cross-over can be induced with a consequent locally high mechanical deformation and potential performance degradation. In this paper, the processes implemented at CERN for preventing and detecting strands cross-over during cables production are presented. The effect of cross-over on the electrical performance of a restack rod process Rutherford cable is also reported and discussed

A single liquid chromatography procedure to concentrate, separate and collect size-selected polyynes produced by pulsed laser ablation in water

Polyynes are linear carbon chains characterized by alternated single and triple bonds and terminated by hydrogen or other terminal substituents. They can be synthesized by pulsed laser ablation in liquid (PLAL) as a scalable, cost-effective, and fast physical technique. Water can be employed as a solvent for PLAL to avoid toxicity problems and to reduce costs compared to organic solvents. However, in in this case, the production yield of polyynes reached is extremely low and prevents further characterization and implementation in new functional materials. In this work, we synthesized polyynes by pulsed laser ablation in water and we optimized the process parameters to improve the yield of polyynes by PLAL. Then, we developed a procedure entirely based on reversed-phase high-performance liquid chromatography (RP-HPLC) which effectively enables the concentration, separation and collection of polyynes according to their length. Since the polyynes sample is an aqueous solution, we could inject it directly into the RP-HPLC column without the dilution step required in the case of a sample in an organic solvent. Thanks to our single RP-HPLC procedure, it is possible to highly increase the concentration and separately characterize different size-selected polyynes for further use in functional materials

In situ synthesis of polyynes in a polymer matrix via pulsed laser ablation in a liquid

Polyynes are finite chains formed by sp-hybridized carbon atoms with alternating single and triple bonds and display intriguing electronic and optical properties. Pulsed laser ablation in liquid (PLAL) is a well assessed technique for the physical synthesis of hydrogen-capped polyynes in solution; however, their limited stability prevents further exploitation in materials for different applications. In this work, polyynes in poly(vinyl alcohol) (PVA) were produced in a single-step PLAL process by ablating graphite directly in an aqueous solution of PVA which, as a participating medium for PLAL, is shown to favour the formation of polyynes. The addition of Ag colloids to the aqueous PVA/polyynes solution allowed surfaceenhanced Raman spectroscopy (SERS) measurements, carried out both on liquid samples and on free-standing nanocomposites, obtained after solvent evaporation. A non-trivial behaviour of the polymer matrix structure as a function of the PVA concentration is revealed showing that an intimate blend of polyynes and Ag nanoparticles with the polymer can be achieved. We demonstrate that polyynes in the nanocomposite remain stable for at least 11 months, whereas the corresponding Ag/ PVA/polyynes solution displayed a strong polyyne decomposition already after 3 weeks. These results pave the way to further characterization of the properties of polyyne-based films and materials

Size-selected polyynes synthesised by submerged arc discharge in water

Polyynes, linear sp-carbon chains of finite length, can be synthesised by submerged arc discharge in liquid, which so far, has been mainly exploited in organic solvents. In this work, we investigated this technique in water as a cheap and non-toxic solvent to produce polyynes. After optimisation of the process parameters, hydrogen-terminated polyynes (CnH2: n = 6-16) were identified by high-performance liquid chromatography with the support of theoretical calculations. Size-selected polyynes were separately analysed by surface-enhanced Raman spectroscopy allowing to assign the bands of mixed polyynes solution to specific wire lengths. Stabilisation strategies for hydrogen-capped polyynes were also studied, obtaining promising results