Influence of pulse-to-pulse delay for 532 nm double-pulse laser-induced breakdown spectroscopy of technical polymers

Laser induced breakdown spectroscopy (LIBS) is an emerging technique for fast and accurate compositional analysis of many different materials. We present a systematic study of collinear double-pulse LIBS on different technical polymers such as polyamide, polyvinyl chloride, polyethylene etc. Polymer samples were ablated in air by single-pulse and double-pulse Nd:YAG laser radiation (8 ns pulse duration) and spectra were recorded with an Echelle spectrometer equipped with an ICCD camera. We investigated the evolution of atomic and ionic line emission intensities for different delay times between the laser pulses (from 20 ns to 500 μs) at a laser wavelength of 532 nm. We observed double-pulse LIBS signals that were enhanced as compared to single-pulse measurements depending on the delay time and the type of polymer material investigated. LIBS signals of polymer materials that are enhanced by double-pulse excitation may be useful for monitoring the concentration of heavy metals in polymer materials.     

On the mechanism of the photoinduced reduction of an adduct of ferricytochrome C with a poly(4-vinylpyridine) polymer containing –Re (CO)3(3,4,7,8-tetramethyl-1,10-phenanthroline) pendants

Changes in the UV–vis absorption spectrum revealed the formation of adducts between the Re^I polymer and ferricytochrome C, Fe^III-Cyt c. Different morphologies for the Re^I polymer and the adducts formed between the Re^I polymer and Fe^III-Cyt c were observed by TEM. The reduction of the Re^I chromophores in the polymer, achieved by the reductive quenching of the MLCT excited state of the Re^I polymer by triethylamine (TEA) and/or by the reaction between e⁻_solv and {[(vpy)₂vpyRe^I(CO)₃(tmphen)⁺]}_n200 in pulse radiolysis experiments, produces –Re^I(CO)₃(tmphen) and –Re^I(CO)₃(tmphenH)⁺ as the main species. The reductive quenching of the MLCT of the Re^I polymer by TEA was followed by a rapid electron transfer from the –Re^I(CO)₃(tmphen) to the Fe^III center in the heme to produce ferrocytochrome C, Fe^II-Cyt c.     

Synthesis of novel hybrid films of a layered silicate and alkylammonium cations on rough polymeric surfaces by Langmuir–Blodgett method

Hybrid films of a layered silicate and an amphiphilic alkylammonium (hexadecyltrimethylammonium) cation have been prepared by Langmuir–Blodgett (LB) method and transferred onto a polyamide surface by dip coating. This is the first time that stable LB hybrid monolayer and multilayer films have been formed on rough polymeric surfaces. The films were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and water contact angle measurements. XRD and FTIR showed that the hybrid multilayer was well-organized and the thickness of one layer was calculated to be 1.6 nm. Furthermore, the layered silicate was determined to be on the substrate side and the amphiphilic molecule layer was exposed to the air side. This provides a novel methodology for the surface modification of polymers.     

Two Coordination Networks Built from p‐Sulfonatothiacalix[4]arene Tetranuclear Clusters

Two coordination compounds based on p‐sulfonatothiacalix[4]arene (TCAS) were synthesized by hydrothermal reactions of TCAS with M²⁺ cations (M = Cu for 1 , M = Co for 2 ) in the presence of [PhCH₂N(CH₃)₃]⁺. Single‐crystal X‐ray analyses revealed that both compounds, 1 and 2 , are isomorphous and crystallize in the same space group . The tetranuclear cluster units are connected into layer networks through complicated hydrogen‐bonding and π–π interactions. The results of thermogravimetric measurements demonstrate that 1 and 2 have the high thermal stabilities.     

Syntheses and Characterization of Two Coordination Polymers Constructed by the Ligand 3,5‐Bis(pyridin‐4‐ylmethoxy)benzoic Acid

Two coordination polymers, namely [Zn(L1)(OAc)]·H₂O ( 1 ) and [Cd(L1)₂] ( 2 ), where L1 = 3,5‐bis(pyridin‐4‐ylmethoxy)benzoic acid, have been synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction analysis. Complex 1 has a 2D layer structure in which the hydrogen bonds between lattice water molecules and uncoordinated carboxylate oxygen atoms of the ligand L1 in the adjacent layers extend the 2D layer into a 3D supramolecular architecture. The structure of 2 is a 2D (3,5)‐connected net with (3·5²)(3²·5³·6⁴·7) topology. In addition, the luminescent properties of complexes 1 and 2 have been studied in the solid state at room temperature.     

Synthesis,Crystal Structure,and Magnetic Properties of a New Coordination Polymer Framework [CoII(4,4′‐bpy)(N3)2]n

A new cobalt(II) coordination polymer containing 4,4′‐bipyridine and azide as bridging ligand, [Co^II(4,4′‐bpy)(N₃)₂]_n ( 1 ) was synthesized under mild hydrothermal conditions and was characterized by single‐crystal X‐ray diffraction studies and magnetic susceptibility measurements. It exhibits an acentric structure, in which cobalt(II) ions are linked through end‐to‐end (EE) azido groups. The 4,4′‐bpy ligands are coordinated on the axial positions of the octahedral environment reinforcing the intermetallic connections and resulting in a network. Circular dichroism spectra of the compound exhibit a maximum negative Cotton effect at 260 nm, which indicates the chiral nature of 1 . Variable temperature magnetic susceptibility measurements in the temperature range 2–300 K reveal the existence of antiferromagnetic couplings in the framework.     

A New Coordination Polymer [Pb(1,4‐BDC)]n Containing a Unique μ6‐Bridging Coordination Mode

A new coordination polymer, [Pb(1,4‐BDC)]_n ( 1 ) (1,4‐H₂BDC = 1,4‐benzenedicarboxylic acid), has been synthesized under solvothermal conditions. Its structure was determined with single‐crystal X‐ray diffraction studies and further characterized by inductively coupled plasma (ICP) spectrometry, elemental analysis, IR spectroscopy, thermogravimetric analysis, and X‐ray powder diffraction studies. The results revealed that complex 1 has a two‐dimensional network with (6, 3) topology observed in the [110] direction. Moreover, the layers are connected into a framework through 1,4‐BDC^2? ligands. The μ₆‐bridging coordination mode adopted by 1,4‐BDC^2? is unprecedented in metal/1,4‐BDC^2? complexes.     

Characterization of chemosynthetic Al2O3-2SiO2 geopolymers

Pure chemosynthetic Al₂O₃-2SiO₂ geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol-gel method. The molecular structure of the precursor powder and resulting geopolymers were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis. In addition, the mechanical and alkali-activated polymerization properties of these materials were also studied. NMR data revealed that the chemosynthetic powders began to contain 5-coordinated Al atoms when the calcination temperatures exceeded 200 °C. These calcined powders were capable of reacting with sodium silicate solutions at calcination temperatures exceeding 300 °C, which is, however, much lower than the temperature required to convert kaolin to Metakaolin.     

Pressure dependence of the Shubnikov-de Haas oscillation spectrum of \beta'-(BEDT-TTF)4(NH4)[ Cr(C2 O4)3] .DMF

The Shubnikov-de Haas (SdH) oscillation spectra of the -(BEDT-TTF)₄(NH₄)[ Cr(C₂O₄)₃] .DMF organic metal have been studied in pulsed magnetic fields of up to either 36 T at ambient pressure or 50 T under hydrostatic pressures of up to 1 GPa. The ambient pressure SdH oscillation spectra can be accounted for by up to six fundamental frequencies which points to a rather complex Fermi surface (FS). A noticeable pressure-induced modification of the FS topology is evidenced since the number of frequencies observed in the spectra progressively decreases as the pressure increases. Above 0.8 GPa, only three compensated orbits are observed, as it is the case for several other isostructural salts of the same family at ambient pressure. Contrary to other organic metals, of which the FS can be regarded as a network of orbits, no frequency combinations are observed for the studied salt, likely due to high magnetic breakdown gap values or (and) high disorder level evidenced by Dingle temperatures as large as ≃7 K.     

Spinodal wrinkling in thin-film poly(ethylene oxide)/polystyrene bilayers

Optical microscopy and atomic force microscopy were used to study a novel roughness-induced wrinkling instability in thin-film bilayers of poly(ethylene oxide) (PEO) and polystyrene (PS). The observed wrinkling morphology is manifested as a periodic undulation at the surface of the samples and occurs when the bilayers are heated above the melting temperature of the semi crystalline PEO (T_m = 63 ) layer. During the wrinkling of the glassy PS capping layers the system selects a characteristic wavelength that has the largest amplitude growth rate. This initial wavelength is shown to increase monotonically with increasing thickness of the PEO layer. We also show that for a given PEO film thickness, the wavelength can be varied independently by changing the thickness of the PS capping layers. A model based upon a simple linear stability analysis was developed to analyse the data collected for the PS and PEO film thickness dependences of the fastest growing wavelength in the system. The predictions of this theory are that the strain induced in the PS layer caused by changes in the area of the PEO/PS interface during the melting of the PEO are sufficient to drive the wrinkling instability. A consideration of the mechanical response of the PEO and PS layers to the deformations caused by wrinkling then allows us to use this simple theory to predict the fastest growing wavelength in the system.