Characterization of stable isotope fractionation during methane production in the sediment of a eutrophic lake,lake dagow,germany

We measured delta C-13 of CO2, CH4, and acetate-methyl in profundal sediment of eutrophic Lake Dagow by incubation experiments in the presence and absence of methanogenic inhibitors chloroform, bromoethane sulfonate (BES), and methyl fluoride, which have different specificities. Methyl fluoride predominantly inhibits acetoclastic methanogenesis and affects hydrogenotrophic methanogenesis relatively little. Optimization of methyl fluoride concentrations resulted in complete inhibition of acetoclastic methanogenesis. Methane was then exclusively produced by hydrogenotrophic methanogenesis and thus allowed determination of the fractionation factors specific for this methanogenic pathway. Acetate, which was then no longer consumed, accumulated and allowed determination of the isotopic signatures of the fermentatively produced acetate. BES and chloroform also inhibited CH4 production and resulted in accumulation of acetate. The fractionation factor for hydrogenotrophic methanogenesis exhibited variability, e. g., it changed with sediment depth. The delta C-13 of the methyl group of the accumulated acetate was similar to the delta C-13 of sedimentary organic carbon, while that of the carboxyl group was by about 12 parts per thousand higher. However, the delta C-13 of the acetate was by about 5 parts per thousand lower in samples with uninhibited compared with inhibited acetoclastic methanogenesis, indicating unusual isotopic fractionation. The isotope data were used for calculation of the relative contribution of hydrogenotrophic vs. acetoclastic methanogenesis to total CH4 production. Contribution of hydrogenotrophic methanogenesis increased with sediment depth from about 35% to 60%, indicating that organic matter was only partially oxidized in deeper sediment layers.

A strategy for synthesis of ion-bonded amphiphilic miktoarm star copolymers via supramolecular macro-RAFT agent

Amphiphilic supramolecular miktoarm star copolymers linked by ionic bonds with controlled molecular weight and low polydispersity have been successfully synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization using an ion-bonded macromolecular RAFT agent (macro-RAFT agent). Firstly, a new tetrafunctional initiator, dimethyl 4,6-bis(bromomethyl)-isophthalate, was synthesized and used as an initiator for atom transfer radical polymerization (ATRP) of styrene to form polystyrene (PSt) containing two ester groups at the middle of polymer chain. Then, the ester groups were converted into tertiary amino groups and the ion-bonded supramolecular macro-RAFT agent was obtained through the interaction between the tertiary amino group and 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (DMP). Finally, ion-bonded amphiphilic miktoarm star copolymer, (PSt)(2)-poly(N-isopropyl-acrylamide)(2), was prepared by RAFT polymerization of N-isopropylacrylamide (NIPAM) in the presence of the supramolecular macro-RAFT agent. The polymerization kinetics was investigated and the molecular weight and the architecture of the resulting star polymers were characterized by means of H-1-NMR, FTIR, and GPC techniques. (c) 2008 Wiley Periodicals, Inc.

One-Step Ionic Liquid-Assisted Electrochemical Synthesis of Ionic Liquid-Functionalized Graphene Sheet Directly from Graphite

Graphite, inexpensive and available in large quantities, unfortunately does not readily exfoliate to yield individual graphene sheets. Here a mild, one-step electrochemical approach for the preparation of ionic-liquid-functionalized graphite sheets with the assistance of an ionic liquid and water is presented. These ionic-liquid-treated graphite sheets can be exfoliated into functionalized graphene nanosheets that can not only be individuated and homogeneously distributed into polar aprotic solvents, but also need not be further deoxidized. Different types of ionic liquids and different ratios of the ionic liquid to water can influence the properties of the graphene nanosheets. Graphene nanosheet/polystyrene composites synthesized by a liquid-phase blend route exhibit a percolation threshold of 0.1 vol % for room temperature electrical conductivity, and, at only 4.19 vol %, this composite has a conductivity of 13.84 S m(-1), which is 3-15 times that of polystyrene composites filled with single-walled carbon nanotubes.

Study on the Cell Structure and Compressive Behavior of Biodegradable Poly(epsilon-caprolactone) Foam

Biodegradable poly(e-caprolactone) (PCL) foams with a series of controlled structures were prepared by using chemical foaming method. The cell morphology was detected by scanning electron microscope (SEM). The compressive behavior of the foams was investigated by uniaxial compression test. The effect of density and structural parameters on the foam compressive behavior was analyzed. It was found that the relative compressive modulus has a power law relationship with relative density. Increasing of both the cell wall thickness and the cell density lead to higher compressive modulus of the foam; however, the cell size has no distinct effect on compressive behavior.

Investigation of Degradation Behavior of Polymer on Surface of Film Due to the Existence of Monochromatic X-ray

Degradation and its temperature dependence of poly(methyl methacrylate) (PMMA) in the blend film of PMMA/SAN were investigated via ire-situ X-ray photoelectron spectroscopy(XPS). The results show that thermal degradation of PMMA takes place at 185, 130, 80 degrees C and even room temperature due to the existence of monochromatic X-ray. Furthermore, the degradation rate depends crucially on the experiment temperature.

The dewetting dynamics of the polymer thin film by solvent annealing

The slippage effect of the polymer chains is investigated in the dewetting process of the polymer solution film. The solvent-induced dewetting is used in our experiments to study the dynamics of hole growth in the dewetting process of the polymer solution film. Our results show that in the case of the low molecular weight polystyrene (PS) film, the slippage effect of the polymer chains is not displayed and the radius of the holes is R similar to exp(t/tau); in the case of the higher molecular weight PS film, the slippage effect of the polymer chain is not valid in the case of the thin film and that is valid in the case of the thick film, and the dynamic process of hole growth divides into three stages (R similar to t, and then R similar to t(x) (2/3 < x < 1), finally, R similar to t). Besides, the solvent and substrate properties also influence the dewetting dynamics of the polymer solution film.

Morphological transition of dry vesicles into onion-like multilamellar micelles induced through heating at high temperature

In this Letter, we report the morphological transition of dry block copolymer vesicles into onion-like multilamellar micelles induced through heating. When the temperature is higher than the glass transition temperature of block copolymer, the vesicles can collapse, and finally form onion-like multilamellarmicelles via micro phase separation. This phenomenon is observed in both A-B and A-B-A block copolymer vesicles, indicating that the technique used in this study can be an alternative method to synthesize multilamellar micelles.

Effect of binary block-selective solvents on self-assembly of ABA triblock copolymer in dilute solution

We have studied the self-assembly of the ABA triblock copolymer (P4VP-b-PS-b-P4VP) in dilute solution by using binary block-selective solvents, that is, water and methanol. The triblock copolymer was first dissolved in dioxane to form a homogeneous solution. Subsequently, a given volume of selective solvent was added slowly to the solution to induce self-assembly of the copolymer. It was found that the copolymer (P4VP(43)-b-PS366-b-P4VP(43)) tended to form spherical aggregate or bilayer structure when we used methanol or water as the single selective solvent, respectively.

Rhythmic Growth-Induced Ring-Banded Spherulites with Radial Periodic Variation of Thicknesses Grown from Poly(epsilon-caprolactone) Solution with Constant Concentration

Birefringent ring-banded spherulites with radial periodic variation of thicknesses were grown from poly(epsilon-caprolactone) (PCL) solutions under conditions for which the Solution concentration was held constant during the whole development of the morphology. The as-grown ring-banded spherulites were investigated by optical (OM) and atomic force (AFM) microscopies, by transmission electron microscopy (TEM) of samples sectioned parallel to the plane of film, and also by electron diffraction (ED) and grazing incidence X-ray diffraction (GIXD) techniques.

Effect of the nature of annealing solvent on the morphology of diblock copolymer blend thin films

The morphologies and structures for the thin film of blend systems consisting of two asymmetric polystyrene-block-polybutadiene (SB) diblock copolymers induced by annealing in the vapor of different solvents, namely, cyclohexane, benzene, and heptane, which have different selectivity or preferential affinity for a certain block, were investigated by tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results revealed that even a slight preferential affinity of good solvent for one block would strongly alter the morphology of the blend thin film.

Sensitive, Label-Free Protein Assay Using 1-ethyl-3-methylimidazolium Tetrafluoroborate Supported Microchip Electrophoresis with Laser-Induced Fluorescence Detection

Based on the dimer-monomer equilibrium movement of the fluorescent dye Pyronin Y (PY), a rapid, simple, highly sensitive, label-free method for protein detection was developed by microchip electrophoresis with LIF detection. PY formed a nonfluorescent dimer induced by the premicellar aggregation of an anionic surfactant, SDS, however, the fluorescence intensity of the system increased dramatically when proteins such as BSA, bovine hemoglobin, cytochrome c, and trypsin were added to the solution due to the transition of dimer to fluorescent monomer. Furthermore, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)) instead of PBS was applied as running buffers in microchip electrophoresis.

Square lamellar structure having phase-separated microdomain in H-shaped block copolymer thin film

The morphology of a H-shaped block copolymer (poly(ethylene glycol) backbone and polystyrene branches (PS)(2)PEG(PS)(2)) in a thin film has been investigated. A peculiar square lamella that has a phase-separated microdomain at its surface is obtained after spin coating. The experimental temperature plays a critical role in the lamellar formation. The copolymer first self-assembles into square lamellar micelles with an incomplete crystalline core due to the crystallizability of PEG.

Fabrication of fibril like aggregates by self-assembly of block copolymer mixtures via interpolymer hydrogen bonding

This paper describes the formation of fibril like aggregates from the self-assembly of block copolymer mixture (polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and polystyrene-b-poly(acrylic acid) (PS-b-PAA)) via interpolymer hydrogen bonding in nonselective solvent. The hydrogen bonding between P4VP and PAA in chloroform leads to the formation of complex. When all the pyridine units in P4VP were all hydrogen bonded to acrylic acid in PAA, the formed complex is insoluble, resulting in the formation of spherical micellar aggregates and nanorods.

Polymer Crystallization Influenced by Initial Orientation of Cylindrical Diblock Copolymers in Thin Films

The effect of the initial states (disordered perpendicular cylinder structure vs. parallel cylinder structure) on the crystallization of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) thin films during cyclohexane annealing was investigated. The cylindrical domains perpendicular or parallel to the surface were obtained by controlling the film thickness. During solvent annealing, for the film with the perpendicular cylinders, the ordering degree of cylinders was increased.

Ring-shaped morphology in H-shaped block copolymer thin films

The formation of ring-shaped structures in an H-shaped block copolymer [a poly(ethylene glycol) backbone with polystyrene branches, i.e., (PS)(2)PEG(PS)(2)] thin film was investigated when it was annealed in saturated PEG-selective acetonitrile vapor. Our results clearly indicate that ring formation is determined by the initial morphology of the spin-coated film, the solvent vapor selectivity and the environmental temperature of the solvent-annealing process. Only the films with the initial core-shell cylindrical structure in strongly PEG-selective acetonitrile vapor could form the ring-shaped structures.