β–Phasiges PVDF–Blockcopolymer: Herkunft, Beeinflussung und Quantifizierung

Das Kristallisationsverhalten von Polyvinylidenfluorid–Blockcopolymeren (PVDF–BC) aus der Reaktionsmischung wurde untersucht. Ziel war es, einen großen Anteil β–phasiges PVDF zu erhalten, da dieses piezoelektrische Eigenschaften aufweist. Die β–Phase ist eine von fünf kristallinen Phasen des PVDFs. Diverse (Meth–)Acrylate wurden für die BC–Synthese in einem Photoreaktor verwendet. Unter anderem konnte gezeigt werden, dass die Bildung von Homopolymer durch das eingesetzte Comonomer vernachlässigt werden kann. Wichtig für ein definiertes PVDF–BC ist eine möglichst hohe Iodendgruppenfunktionalität FI,tot. in der radiklaischen Polymerisation. Mittels GPC, NMR, DSC, IR–PAS und XRD wurden die BC– Produkte analysiert und der Umsatz des PVDFs zum BC bestätigt. Durch IR–PAS und XRD wurde die Phasenkomposition des PVDFs betrachtet. Als Faktor zur Ausbildung hoher Anteile der piezoelektrischen Phase hat sich die Aufarbeitung der Reaktionslösung erwiesen. Die Anwesenheit von Additiven im Antisolvens (MeOH), mit dessen Hilfe das PVDF–BC aus der Lösung durch Auskristallisieren/–fällen erhalten wird, zeigt eine dirigierende Wirkung auf die Phasenkomposition. Es wurden sowohl mehrere in MeOH lösliche Salze (CaCl2, KI, KCl, KBr, NaCl und LiCl) als auch Wasser und KOH bzw. konz. HCl als Zusätze in Kristallisationsexperimenten untersucht. Je höher die Konzentration der gelösten Ionen war, desto größer war der Anteil der β–Phase im PVDF–BC. Im Moment des Mischens der Reaktionslösung mit dem Antisolvens wirken kurzzeitig an der Grenzfläche die gelösten Ionen mit ihrer Ladung auf die partiell geladenen Segmenten des PVDFs. So kann z. B. ein negativ geladenes Ion mit den partiell positiv geladenen CH2–Einheiten des PVDFs wechselwirken. Dieser Einfluss wird durch die Polarität der Lösungsmittel (DMAc und MeOH) und eventuell anwesendem Wasser unterstützt. Die all–trans–Konformation wird vorgegeben und fungiert als Kristallisationskeim beim Ausfällen des PVDF–Blockcopolymers. Zur Quantifizierung des effektiven β–Phasengehalts wurde eine neue Größe eingeführt: wβ, Massenprozent β–Phase. Dieses berücksichtigt, neben dessen Gehalt F(β) im kristallinen Anteil, die Kristallinität im PVDF als auch dessen Verhältnis zu einer Nicht–PVDF– Komponente. Im Folgenden wurde durch eine variierte Aufarbeitungsmethode der kristalline Anteil im PVDF–BC erhöht, um somit den Anteil der effektiven β–Phase zu steigern. Eine Zugabe des Fällmediums (MeOH plus konz. HCl) zur Reaktionsmischung unter Rühren und Temperieren auf 50 °C bis zur ersten Trübung und langsamen Abkühlen über Nacht auf RT zeigte die besten Ergebnisse mit einer typischen PVDF/PMMA–BC–RL aus einer Photoreaktorsynthese. Ein Gehalt wβ von ca. 30 w/w–% ist somit erreichbar, was den Verlust an Kristallinität durch die Ausbildung eines Blockcopolymers wettmacht. Durch weitere Optimierung der Ausfällmischung konnte wβ durch den Zusatz von konz. HCl und zusätzlichem Wasser in MeOH für ein typisches PVDF/PMMA–BC auf 40 w/w–% gesteigert werden und liegt somit doppelt so hoch wie im verwendeten Ausgangs–PVDF für die BC–Synthese.The crystallization behavior of polyvinylidene fluoride block copolymers (PVDF–BC) from the reaction mixture was investigated. The objective was to obtain a large fraction of β–phase containing PVDF, since it exhibits piezoelectric properties. The β–phase is one of five crystalline phases of PVDF. Various (meth)acrylates were used for BC synthesis in a photoreactor. Among others, it was shown that the formation of homopolymer by the comonomer used can be neglected. It is important for a defined PVDF–BC to have a high end group functionality FI,tot. of the PVDF starting material in the radical polymerization. By GPC, NMR, DSC, IR–PAS and XRD, the BC products were analyzed and the conversion of PVDF to BC was confirmed. By IR–PAS and XRD, the phase composition of the PVDF was evaluated. The workup of the reaction solution was found to be a factor in the formation of high proportions of the piezoelectric phase. The presence of additives in the antisolvent (MeOH), with the help of which the PVDF-BC is obtained from the solution by crystallization/precipitation, shows a directing effect on the phase composition. Several salts soluble in MeOH (CaCl2, KI, KCl, KBr, NaCl and LiCl) as well as water and KOH or conc. HCl as additives were investigated in crystallization experiments. The higher the concentration of the dissolved ions was, the greater was the proportion of the β–phase in the PVDF–BC. At the moment of mixing the reaction solution with the antisolvent, the dissolved ions act briefly at the interface with their charge on the partially charged segments of the PVDF. For example, a negatively charged ion can interact with the partially positively charged CH2 units of the PVDF. This influence is supported by the polarity of the solvents (DMAc and MeOH) and any water present. The all-trans conformation is prescribed and acts as a crystallization nucleus upon precipitation of the PVDF block copolymer. To quantify the effective β–phase content, a new parameter was introduced: wβ, mass percent of β–phase. This takes into account, besides the content F(β) in the crystalline fraction, the crystallinity in the PVDF as well as its ratio to a non-PVDF component. In the following, the crystalline fraction in the PVDF-BC was increased by a varied workup method in order to increase the fraction of the effective β–phase. Adding the precipitation medium (MeOH plus conc. HCl) to the reaction mixture while stirring and tempering to 50 °C until the first turbidity appears and slowly cooling overnight to RT showed the best results with a typical PVDF/PMMA-BC RM from a photoreactor synthesis. A content of about 30 w/w-% is achievable in this way, which compensates for the loss of crystallinity due to the formation of a block copolymer. By further optimizing the precipitation mixture, the addition of conc. HCl and additional water in MeOH for a typical PVDF/PMMA-BC wβ could be increased to 40 w/w-%, which is twice as high as in the starting PVDF used for BC synthesis

Sydnone methides - a forgotten class of mesoionic compounds for the generation of anionic N-heterocyclic carbenes

Sydnone methides are described from which only one single example has been mentioned in the literature so far. Their deprotonation gave anions which can be formulated as π-electron rich anionic N-heterocyclic carbenes. Sulfur and selenium adducts were stabilized as their methyl ethers, and mercury, gold as well as rhodium complexes of the sydnone methide carbenes were prepared. Sydnone methide anions also undergo C−C coupling reactions with 1-fluoro-4-iodobenzene under Pd(PPh3)4 and CuBr catalysis. 77Se NMR resonance frequencies and 1JC4-Se as well as 1JC4-H coupling constants have been determined to gain knowledge about the electronic properties of the anionic N-heterocyclic carbenes. The carbene carbon atom of the sydnone methide anion 3 j resonates at δ=155.2 ppm in 13C NMR spectroscopy at −40 °C which is extremely shifted upfield in comparison to classical N-heterocyclic carbenes

Formation of titanium nitride, titanium carbide, and silicon carbide surfaces by high power femtosecond laser treatment

Coatings based on titanium nitrides, titanium carbides and silicon carbides can optimize the surface properties of titanium or silicon for various applications ranging from biocompatibility to chemical stability and durability. Here, we investigated a high power (100 W) high pulse repetition rate femtosecond laser process (λ=1030 nm, τ=750 fs, f=1 MHz) for the treatment of titanium and silicon in atmospheres of argon, nitrogen, methane, ethene and acetylene. In a nitrogen atmosphere, a homogeneous coating of TiON is formed on titanium. In an ethene/argon atmosphere coatings of TiOC and SiC are formed on Ti and Si, respectively. The process allows a fast surface transformation with a process rate of 0.33 cm2 s−1 and a high spatial resolution below 0.5 mm with a minimal heat affected zone at the same time. In contrast to low repetition rate femtosecond laser processed samples, the surfaces are more robust against mechanical impact. At the same time, the surfaces reveal a distinct microstructure in comparison to coatings obtained by vapor deposition techniques

Customizing the appearance of sparks with binary metal alloys

Long-flying sparks are an essential part of several pyrotechnic effects. Unfortunately, and in contrast to colored flames, the color space of sparks is basically limited to the black-body curve. With low-boiling metals, vapor phase combustion and bright colorful flashes are achievable. In 1999, alloys of rare-earth elements have been proposed for colorful spark genera-tion. To the best of our knowledge, here we present the first investigation of such alloys to change the color of sparks be-yond the black-body limit. Alloys consisting of >65 at.-% of a brightly emitting and low-boiling metal and a carrier metal allow achieving long-flying deeply colored sparks. Besides the color, branching of sparks is crucial for the visual appear-ance. Rare-earth metals were found to promote branching of different alloys. Finally, fountains ejecting golden/green sparks based on a stable eutectic Yb-Cu alloy and continuously branching sparks based on Nd2Fe14B are presented

Ethynyl-Bridged Bis-quinolinium Dyes : Studies of the Dependence of Different Types of Conjugation on Spectroscopic Properties

Dicationic bis-quinolinium salts possessing different types of conjugation are presented in which the hetareniums are separated by acetylenic or 1,4-diethynylbenzene spacers. Cross-conjugation is induced by interconnections via the 3-positions of the heteroareniums, and conjugation is realized by 2,2/2,4/4,4-interconnections. We also synthesized mixed cross-conjugated/conjugated 2,3/4,3-interconnected species. The different types of conjugation determine the charge distribution according to the rules of resonance which translate into characteristic C-13 NMR as well as UV-Vis-spectroscopic properties, LUMO geometries, and chemical properties. We found that the triple bond's resonance frequencies are sensitive C-13 NMR spectroscopic indicators for the type of conjugation. Combining cross-conjugated and conjugated structure elements of dicationic bis-quinolinium dyes via triple bonds without additional benzene spacer results in considerable bathochromic shifts of the UV-Vis absorption maxima [Delta lambda(max)approximate to 100 nm]. A charge transfer was calculated from the HOMO of the conjugated into the LUMO of the cross-conjugated partial structure.Peer reviewe

3D-Printing inside the glovebox: a versatile tool for inert-gas chemistry combined with spectroscopy

3D-Printing with the well-established ‘Fused Deposition Modeling’ technology was used to print totally gas-tight reaction vessels, combined with printed cuvettes, inside the inert-gas atmosphere of a glovebox. During pauses of the print, the reaction flasks out of acrylonitrile butadiene styrene were filled with various reactants. After the basic test reactions to proof the oxygen tightness and investigations of the influence of printing within an inert-gas atmosphere, scope and limitations of the method are presented by syntheses of new compounds with highly reactive reagents, such as trimethylaluminium, and reaction monitoring via UV/VIS, IR, and NMR spectroscopy. The applicable temperature range, the choice of solvents, the reaction times, and the analytical methods have been investigated in detail. A set of reaction flasks is presented, which allow routine inert-gas syntheses and combined spectroscopy without modifications of the glovebox, the 3D-printer, or the spectrometers. Overall, this demonstrates the potential of 3D-printed reaction cuvettes to become a complementary standard method in inert-gas chemistry

Геофизический прогноз нового перспективного участка в партизанском золоторудном узле (Енисейский кряж)

Рассматривается обоснование аэрогеофизических признаков золото-сульфидно-вкрапленного оруденения на новом участке в Партизанском рудном узле -Подголечном, предположительно аналогичного месторождению Благодатному Северо-Енисейского района (Енисейский кряж), по результатам съемки 2012 г. (магнитометрия, электроразведка ДИП-А, гамма-спектрометрия) масштаба 1:10000

Switchable mesomeric betaines derived from pyridinium-phenolates and bis(thienyl)ethane

Syntheses of push–pull substituted non-symmetric bis(thienyl)ethenes (BTEs) possessing a central perfluorocyclopentene core are described. The substituent effects of anisole, phenole, and phenolate as well as pyridine, pyridinium, and N-methylpyridinium substituents, joined through their 3- or 4-positions to the central BTE core, respectively, cover the range from very strongly electron-donating [σ(4-phenolate)=−1.00] to extremely strongly electron-withdrawing [σ(pyridinium-4-yl)=+2.57] in the title mesomeric betaines. The different isomers possessing 4-yl/4-yl, 4-yl/3-yl and 3-yl/3-yl substituents represent different combinations of conjugated and cross-conjugated partial structures and cause different spectroscopic properties. In addition, through-space conjugation between the 2- and 2′-position of the thiophenes can be observed which circumvents the charge-separation of through-bond cross-conjugation. The BTE possessing the push–pull chromophore consisting of 3-anisole and 4-pyridinium substituents (24) displays the best extinction coefficients within the series of compounds described here (ϵ=33.8/15.7 L/mol ⋅ cm), while the mesomeric betaine possessing an N-methylpyridinium-4-yl and a 4-phenolate substituent (29) displays considerable bathochromic shifts to λmax=724 nm in its closed form

Depth-size trends in western Mediterranean demersal deep-sea fishes

Se discute y argumenta la distribución de los peces en función de su talla. Gráficos, Tallas, Tablas.We analyze the bathymetric trends of demersal deep-sea flshes in the Catalan Sea (NW Medlterranean) between 1000 and 2250 m depth In the first part of the study, only the pattern shown by the whole fauna (wthin-fauna pattern ) 1s considered At 1200 m there is a significant decrease In fish mean welght, as a consequence of the replacement of the dominant large or medium-sized specles by small ones This fauna1 shift may be a consequence of the lower trophic availability at greater depths, as shown by an important decrease in megafaunal biomass between 1000 and 2250 m In the second part, the study focuses on the depth-size trends of the most common species (within-species pattern) Results show that the bigger-deeper phenomenon is not a well-estabhshed tendency None of the lower slope species and only 2 of the 5 middle slope species analyzed behave as bigger-deeper species Moreover some specles which display a bigger-deeper trend in North Atlantic waters do not show any significant trend In the Medlterranean Considering the recent Atlantic origin of Mediterranean ichthyofauna and the contrasting behaviour in the 2 areas, the hypothesis that mean slze increase with depth is the result of inherited ontogenic behaviour can be discarted.Research program BATIMAR (CSICCAICYT; reference PAC 86-008/ID 821).Peer reviewe