Properties of Single- and Double-Lap Polymeric Joints Welded by a Diode Laser

Single-lap and double-lap polymeric joints of ultrahigh molecular weight polyethylene (UHMWPE) sheets, opportunely overlapped, were realized and studied. One of the polymer sheets was doped with carbon nanomaterials as a laser-absorbent filler. The joints were irradiated by a diode laser operating at 970 nm with maximum pulse energy of 200 mJ. Four types of weld seam geometries were realized in the overlapped area. Optical microscopy observations and mechanical shear and hardness tests were performed in order to characterize all the prepared joints. The maximum shear load was ≈210 N, reached generally in the double-lap joints. High loads in the single-lap joints were reached if high surface area of the welding and high filler amount in the polymer were present. Three parameters influenced the joint resistance: the joint configuration (single or double lap), the welding geometry, and the filler amount. The absorption of diode laser energy at the sheet interface induces a melting process that softens the polymeric sheets in the laser contact area. Finally, a comparison between the welding ability of the diode laser and of the Nd:Yag laser upon the polyethylene sheets is presented.     

Lithium ions conduction in Li2xMn1-xPS3 films

Li_2xMn_1-xPS₃ films have been synthesized by exfoliating MnPS₃ through the successive intercalations of K⁺ and Li⁺ ions. Their dielectric response has been measured from 80 to 350 K in the frequency range of (10²–10⁶) Hz. The obtained data have been analyzed in terms of both complex permittivity ε* and the ac conductivity σ_ac. The frequency dependence of σ_ac has been interpreted in terms of the Jonscher’s law, whose exponent n decreases by increasing temperature. The n values lie between 0.479 and 0.501 and are typical of materials in which the ac conductivity is due to multiple hops of carriers. By analyzing the σ_dc temperature dependence, the observed dielectric response has been attributed to the intercalated lithium ions, and the Li_2xMn_1-xPS₃ films have been classified as hopping charge carrier systems.     

Partial reduction of graphene oxide upon intercalation into exfoliated manganese thiophosphate

Abstract

We have prepared novel nanohybrid Li_2xMn_1?xPS₃/GO films consisting of graphene oxide (GO) and exfoliated MnPS₃ nanosheets via an easy mixing protocol at room temperature. These films were investigated by SEM and AFM, as well as XRD, Raman and XPS spectroscopies, obtaining information about the nature of the interaction between MnPS₃ and GO. In particular, the dark colour of the nanocomposite film and, more to the point, the analysis of (i) the C1s core level XPS spectra, (ii) the interlayer spacing obtained by XRD measurements and (iii) the increment in the intensity ratio I_D/I_G of the two bands typical of the carbon region of GO Raman spectra, suggest that a partial reduction of GO can be obtained right upon intercalation into Li_2xMn_1?xPS₃.     

Visible luminescence spectroscopy of free-base and zinc phthalocyanines isolated in cryogenic matrices

The absorption, emission and excitation spectra of ZnPc and H(2)Pc trapped in Ne, N(2), Ar, Kr and Xe matrices have been recorded in the region of the Q states. A comparison of the matrix fluorescence spectra with Raman spectra recorded in KBr pellets reveals very strong similarities. This is entirely consistent with the selection rules and points to the occurrence of only fundamental vibrational transitions in the emission spectra. Based on this behaviour, the vibronic modes in emission have been assigned using results obtained recently on the ground state with large basis-set DFT calculations [Murray et al. PCCP, 12, 10406 (2010)]. Furthermore, the very strong mirror symmetry between excitation and emission has allowed these assignments to be extended to the excitation (absorption) bands. While this approach works well for ZnPc, coupling between the band origin of the S(2)(Q(Y)) state and vibrationally excited levels of S(1)(Q(X)), limits the range of its application in H(2)Pc. The Q(X)/Q(Y) state coupling is analysed from data obtained from site-selective excitation spectra, revealing pronounced matrix and site effects. From this analysis, the splitting of the Q(X) and Q(Y) states has been determined more accurately than in any previous attempts.     

Effective cell uptake of nanoassemblies of a fluorescent amphiphilic cyclodextrin and an anionic porphyrin

An emitting nanoassembly composed of a novel amphiphilic cyclodextrin functionalised with a covalently appended fluorophore and an anionic porphyrin internalizes effectively in tumor cells, allowing simultaneously the detection of carrier and photosensitiser.     

Metal-mediated self-assembly of tetrapyridyl porphyrins by Na+ ions

In the presence of the sodium salt of a bulky anion, which allows the solubility of Na(+) in low polarity solvents, various tetra(4-pyridyl)porphyrin derivatives can spontaneously self-assemble from CH(2)Cl(2) into supramolecular nanostructures exhibiting a long-range order, through the coordination of Na(+) ions by the pyridyl moieties at the macrocycle periphery.     

Photochemistry of acetylacetone isolated in parahydrogen matrices upon 266 nm irradiation

The photochemistry of the chelated enol form of acetylacetone (AcAc) was investigated by UV excitation of the S(2) state at 266 nm in parahydrogen matrices, complemented by experiments in neon and normal hydrogen matrices. Infrared (IR) spectroscopy, combined with theoretical calculations, was used to identify the photoproducts. Isomerization towards various non-chelated forms (no intramolecular H-bond) of AcAc is the dominant channel whereas fragmentation is very minor. The isomerization kinetics is monitored by IR spectroscopy. Among the seven non-chelated conformers of AcAc, only three are formed in parahydrogen matrices, whereas four are observed in normal hydrogen matrices. This difference suggests that an active tunnelling process between conformers occurs in parahydrogen but is quenched in normal hydrogen where guest-host interactions are stronger. Fragmentation and isomerization of excited AcAc are discussed in the light of these new data. The role of the intermediate triplet state in the S(2)→ S(0) relaxation is confirmed, as the importance of phonons in the condensed phase.     

One‐, two‐, and three‐electron bonding: An “in vitro” theoretical study using noninteger nuclear charges evidences the crucial role of electronegativity in the strength of symmetrical bonds

Fictitious hydrogen atoms H*_A of variable nuclear charge 0.5 ≤ Z_A ≤ 2 (and thus of variable electronegativity) are used to study the intrinsic dependency of chemical bonding on electronegativity. Dissociation energy and equilibrium distance are reported for symmetrical 1‐, 2‐ and 3‐electron H*_AH*_A systems and 2‐electron dissymmetrical H*_A‐H ones. Dealing with symmetrical systems, the strongest two‐electron bonds are found for Z_A ≈ 1.2. Oneelectron and three‐electron strongest bonds occur respectively with low (ca. 0.7) and high (ca. 1.7) Z_A values and can become stronger than the corresponding 2‐electron system. Comparison with data on real systems leads to conclude that electronegativity is a prevailing atomic property in the control of the dissociation energy of symmetrical 1‐, 2‐ and 3‐electron bonds. A simplified mathematical model at Hartree‐Fock or Heitler‐London level with a minimal basis set reproduces these trends semi‐quantitatively and provides the overall shape of the dissociation curves. Finally some points are qualitatively discussed from MO analysis, which emphasize the dependence of the bonding/antibonding properties on the nucleus charge Z_A and their occupancy number. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Electrosynthesis of structured derivated polythiophenes: Application to electrodeposition of latex particles on these substrates

Synthesis of super-structured polymers is a great challenge because these entities could present a large choice of applications. Synthesis and electropolymerisation of thiophene derivatives are reported. Star-shaped 3D molecules are chosen because these structures ensure a high electronic conductivity. Three-dimensional structures could also assist the conductivity. 1,3,5-tris[5-(2,2′-dithienyl)]benzene 1, tris(2,2′-dithienyl)methylcarbinol 2, tris(5(2,2′:5′2″-terthienyl)methylcarbinol 3 are synthetised by different ways. UV and IR analysis are reported along with an AFM examination of the film. The first attempt of latex particle deposition on the film is also reported showing promising results in view of surface functionalisation.     

Confocal Raman imaging and atomic force microscopy of the surface reaction of NO2 and NaCl(100) under humidity

Polarized confocal Raman imaging combined with non‐contact atomic force microscopy (AFM) was used to study the three‐dimensional evolution of the NaCl(100) surface during its reaction with NO₂ at low pressure as a function of relative humidity (RH) from 0% to nearly 80%. Sea salt particles containing NaCl as the main constituent are believed to be the major source of reactive tropospheric chlorine and nitrate fallouts. At an RH of 0%, the reaction of dry NO₂ generates surface conversion to NaNO₃ monolayer capping the NaCl(100) surface and releases NOCl. The subsequent exposure of this NaNO₃ layer to RH below ∼45% induces the formation of rare NaNO₃ tetrahedral crystals less than 0.5 µm in size. The crystallization occurs through two‐dimensional NO₃⁻ migration under the H₂O monolayer regime. After another subsequent exposure to RH above 45% and below 75%, supermicrometric NaNO₃ rhombohedral plates were obtained under the H₂O multilayer regime. On the other hand, the simultaneous exposure of NaCl(100) to NO₂ and H₂O below ∼45% RH rapidly generates numerous submicrometric NaNO₃ tetrahedra on the NaCl(100) surface. The dramatic increase of NaNO₃ production in the presence of water vapour is explained by the formation of HNO₃ and its easy reaction with the NaCl(100) surface. For RH above 45% and below 75%, the tetrahedra evolve to rhombohedral plates of supermicrometric size. The exposure of NaCl(100) to NO₂/H₂O mixtures under RH above 75% induces the coexistence of both solid‐state NaNO₃ and dissolved NO₃⁻ in droplets. Copyright © 2008 John Wiley & Sons, Ltd.