Conducting polymer wires in mesopore hosts

Nanometer-size conducting structures are of great interest in view of fundamental issues and potential applications. We explore the inclusion chemistry of conjugated polymers and graphite-like materials as a means to create such structures. Novel mesoporous materials with pore diameters in the 3 nm range (MCM-41) are used as hosts. Monomer molecules are introduced via vapor or solution transfer and polymerized either by included or external reagents. The properties of the conjugated systems are studied while encapsulated or after dissolution of the host. In the case of polyaniline formed on oxidation of aniline with persulfate, microwave absorption shows the presence of conducting filaments in the host channels. The above systems are compared with graphite-type material encapsulated in MCM-41 by first forming a precursor polymer such as polyacrylonitrile that is pyrolyzed at 500-800°C. These polymer chains are the first nanometer-size conducting filaments stabilized in a well-defined channel host

Molecular Orbital Models of Benzene, Biphenyl and the Oligophenylenes

A two state (2-MO) model for the low-lying long axis-polarised excitations of poly(p-phenylene) oligomers and polymers is developed. First we derive such a model from the underlying Pariser-Parr-Pople (P-P-P) model of pi-conjugated systems. The two states retained per unit cell are the Wannier functions associated with the valence and conduction bands. By a comparison of the predictions of this model to a four state model (which includes the non-bonding states) and a full P-P-P model calculation on benzene and biphenyl, it is shown quantitatively how the 2-MO model fails to predict the correct excitation energies. The 2-MO model is then solved for oligophenylenes of up to 15 repeat units using the density matrix renormalisation group (DMRG) method. It is shown that the predicted lowest lying, dipole allowed excitation is ca. 1 eV higher than the experimental result. The failure of the 2-MO model is a consequence of the fact that the original HOMO and LUMO single particle basis does not provide an adequate representation for the many body processes of the electronic system.Comment: LaTeX, 12 pages, 3 eps figures included using epsf. To appear in Chemical Physics, 199

Environmental impact of cadmium: a review by the Panel on Hazardous Trace Substances.

This report is the result of a review by a Panel on Hazardous Trace Substances, as part of a report to an ad hoc Committee on Environmental Health Research whose chairman was Dr. David Rall, Director of the National Institute of Environmental Health Sciences, NIH

The role of glacier mice in the invertebrate colonisation of glacial surfaces: the moss balls of the Falljökull, Iceland

Glacier surfaces have a surprisingly complex ecology. Cryoconite holes contain diverse invertebrate communities while other invertebrates, such as Collembola often graze on algae and windblown dead organic on the glacier surface. Glacier mice (ovoid unattached moss balls) occur on some glaciers worldwide. Studies of these glacier mice have concentrated on their occurrence and mode of formation. There are no reports of the invertebrate communities. But, such glacier mice may provide a suitable favourable habitat and refuge for a variety of invertebrate groups to colonise the glacier surface. Here we describe the invertebrate fauna of the glacier mice (moss balls) of the Falljökull, Iceland. The glacier mice were composed of Racomitrium sp. and varied in size from 8.0 to 10.0 cm in length. All glacier mice studied contained invertebrates. Two species of Collembola were present. Pseudisotoma sensibilis (Tullberg, 1876) was numerically dominant with between 12 and 73 individuals per glacier mouse while Desoria olivacea (Tullberg, 1871) occurred but in far lower numbers. Tardigrada and Nematoda had mean densities of approximately 200 and 1,000 respectively. No Acari, Arachnida or Enchytraeidae were observed which may be related to the difficulty these groups have in colonizing the glacier mice. We suggest that glacier mice provide an unusual environmentally ameliorated microhabitat for an invertebrate community dwelling on a glacial surface. The glacier mice thereby enable an invertebrate fauna to colonise an otherwise largely inhospitable location with implications for carbon flow in the system

Towards a Safe Lithium–Sulfur Battery with a Flame‐Inhibiting Electrolyte and a Sulfur‐Based Composite Cathode

Of the various beyond‐lithium‐ion batteries, lithium–sulfur (Li‐S) batteries were recently reported as possibly being the closest to market. However, its theoretically high energy density makes it potentially hazardous under conditions of abuse. Therefore, addressing the safety issues of Li‐S cells is necessary before they can be used in practical applications. Here, we report a concept to build a safe and highly efficient Li‐S battery with a flame‐inhibiting electrolyte and a sulfur‐based composite cathode. The flame retardant not only makes the carbonates nonflammable but also dramatically enhances the electrochemical performance of the sulfur‐based composite cathode, without an apparent capacity decline over 750 cycles, and with a capacity greater than 800 mA h −1  g −1 (sulfur) at a rate of 10 C. Feuertaufe : Eine nichtentzündbare Schwefelkompositkathode zeigt eine stabile elektrochemische Aktivität über 750 Zyklen und eine Entladungskapazität von über 800 mA h −1  g −1 (Schwefel) mit einer Entladerate von 10 C in einem feuersicheren Elektrolyten. Der Elektrolyt wurde aus einem Phosphitadditiv erzeugt, das an Grenzflächenreaktionen an der Kathode teilnimmt und die Lithiumionendiffusion um das mehr als Zehnfache beschleunigt.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108645/1/ange_201405157_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/108645/2/10263_ftp.pd

Fabrication of Poly(p-Phenylene)/Zeolite Composites and Their Responses Towards Ammonia

Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl3. The electrical conductivity response of the doped PPP (dPPP) towards CO, H2 and NH3 is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H2), but it shows a definite negative response towards NH3. The electrical conductivity sensitivity of dPPP increases linearly with increasing NH3 concentration. To improve the sensitivity of the sensor towards NH3, ZSM-5 zeolite is added into the conductive polymer matrix. The electrical sensitivity of the sensor increases with increasing zeolite content up to 30%. The effect of the type of cation in the zeolite pores is investigated: namely, Na+, K+, NH4+ and H+. The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order: K+ < no zeolite < Na+ < NH4+ < H+. The variation in electrical sensitivity with cation type can be described in terms of the acid-base interaction, the zeolite pore size and surface area. The PPP/Zeolite composite with H+ possesses the highest electrical sensitivity of −0.36 since H+ has the highest acidity, the highest pore volume and surface area, which combine to induce a more favorable NH3 adsorption and interaction with the conductive polymer