Application of static and dynamic enclosures for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux

A static enclosure method was applied to determine the exchange of dimethyl sulfide (DMS) and carbonyl sulfide (OCS) between the surface of Sphagnum peatlands and the atmosphere. Measurements were performed concurrently with dynamic (flow through) enclosure measurements with sulfur-free air used as sweep gas. This latter technique has been used to acquire the majority of available data on the exchange of S gases between the atmosphere and the continental surfaces and has been criticized because it is thought to overestimate the true flux of gases by disrupting natural S gas gradients. DMS emission rates determined by both methods were not statistically different between 4 and >400 nmol m−2 h−1, indicating that previous data on emissions of at least DMS are probably valid. However, the increase in DMS in static enclosures was not linear, indicating the potential for a negative feedback of enclosure DMS concentrations on efflux. The dynamic enclosure method measured positive OCS flux rates (emission) at all sites, while data using static enclosures indicated that OCS was consumed from the atmosphere at these same sites at rates of 3.7 to 55 nmol m−2 h−1. Measurements using both enclosure techniques at a site devoid of vegetation showed that peat was a source of both DMS and OCS. However, the rate of OCS efflux from decomposing peat was more than counterbalanced by OCS consumption by vegetation, including Sphagnum mosses, and net OCS uptake occurred at all sites. We propose that all wetlands are net sinks for OCS.

Lattice Boltzmann study of hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg-Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn-Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage.

Defect evolution and hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

The effects of hydrodynamic interactions on the lamellar ordering process for two-dimensional quenched block copolymers in the presence of extended defects and the topological defect evolutions in lamellar ordering process are numerically investigated by means of a model based on lattice Boltzmann method and self-consistent field theory. By observing the evolution of the average size of domains, it is found that the domain growth is faster with stronger hydrodynamic effects. The morphological patterns formed also appear different. To study the defect evolution, a defect density is defined and is used to explore the defect evolutions in lamellar ordering process. Our simulation results show that the hydrodynamics effects can reduce the density of defects. With our model, the relations between the Flory-Huggins interaction parameter chi, the length of the polymer chains N, and the defect evolutions are studied.

Synthesis and characterization of novel sulfonated poly(arylene ether ketone) copolymers with pendant carboxylic acid groups for proton exchange membranes

A series of novel side-chain-type sulfonated poly(arylene ether ketone)s with pendant carboxylic acid groups copolymers (C-SPAEKs) were synthesized by direct copolymerization of sodium 5,5'-carbonyl-bis(2-fluorobenzenesulfonate), 4,4'-difluorobenzophenone and 4,4'-bis(4-hydroxyphenyl) valeric acid (DPA). The expected structure of the sulfonated copolymers was confirmed by FT-IR and H-1 NMR. Membranes with good thermal and mechanical stability could be obtained by solvent cast process. It should be noted that the proton conductivity of these copolymers with high sulfonation degree (DS > 0.6) was higher than 0.03 S cm(-1) and increased with increasing temperature. At 80 degrees C, the conductivity of C-SPAEK-3 (DS = 0.6) and C-SPAEK-4 (DS = 0.8) reached up to 0.12 and 0.16 S cm-1, respectively, which were higher than that of Nafion 117 (0.10 S cm(-1)).

In situ chlorinating-graft copolymerization on isotactic polypropylene in gas-solid phase

A novel method in situ chlorinating-graft copolymerization (ISCGC) of grafting maleic anhydride (MAH) on isotactic polypropylene (iPP) in gas-solid phase was investigated in this paper. Chlorine (Cl-2) was used as initiator, chlorinating agent and termination agent at the same time during the reaction. The iPP was chlorinated as well as grafted with MAH in the reaction process. The product with chlorine and MAH in the same molecule was named as PP-cg-MAH. Existence of PP-cg-MAH was identified by Fourier transform infrared. Thermal behavior and crystallinity of PP-cg-MAH were analyzed by differential scanning calorimetry, X-ray diffraction and polarizing microscope. Influencing factors for the value of graft degree were also discussed. Compared with conventional peroxide initiated graft method, ISCGC revealed higher MAH graft efficiency (33%), and particularly alleviated degradation of iPP. iPP could be grafted successfully and without changing physical properties dramatically through this method.

Counterion exchange at the surface of polyelectrolyte multilayer film for wettability modulation

Counterions present at the surface of polyelectrolyte multilayers (PEMs) were utilized for modulation of surface wettability via ion exchange. The PEM film was dipped in aqueous solutions of different anions, respectively, and the water contact angle of the surface varied from about 10 degrees to 120 degrees, depending on the hydration characteristics of the anion. The ion exchange mechanism was verified by X-ray photoelectron spectroscopy. The process was rapid and reversible. Ionic strength of the polyelectrolyte solution used for preparing the PEMs was found to be crucial to the surface wetting properties and the reversibility and kinetics of the process, and the effects were correlated to the surface density of the excess charge and counterion. This work provides a general, facile and rapid approach of surface property modulation.

Synthesis and gas permeability of novel fluorinated poly(phenylene-co-naphthalimide)s

A new class of high-performance polymers [poly(phenylene-co-naphthalimide)s] was prepared through the Ni(0) catalytic coupling of N-(4-chloro-2-trifluromethylphenyl)-5-chloro-1,8-naphthalimide and 2,5-dichlorobenzophenone. The resulting copolymers exhibited high molecular weights (high inherent viscosities) and a combination of desirable properties such as good solubility in dipolar aprotic solvents, film-forming capability, and mechanical properties. The glass-transition temperatures of the copolymers ranged from 320 to 403 degrees C and increased as the content of the naphthalimide moiety increased. Tough polymer films, obtained via casting from N-methylpyrrolidone solutions, had tensile strengths of 64-107 MPa and tensile moduli of 3.4-4.7 GPa. The gas permeability coefficients of the copolymers were measured for H-2, CO2, O-2, CH4, and N-2. They showed oxygen permeability coefficients and permeability selectivity of oxygen to nitrogen (permeability coefficient for O-2/permeability coefficient for N-2) in the ranges of 1.39-4.31 and 4.92-5.38 barrer, respectively.

Effects of acetic acid on product selectivity in gas phase oxidative dehydrogenation of cyclohexane

The effect of adding acetic acid on the product distribution in gas phase oxidative dehydrogenation of cyclohexane over alpha(1)-VOPO4 catalyst was investigated. The role of acetic acid in the reaction process was put forward. The proposed mechanism is that acetic acid take precedence of cyclohexane adsorbing on the active sites of alpha(1)-VOPO4 catalyst to form isolated active site. Thus, cyclohexene species can desorb quickly from the active sites, avoiding its deep oxidation dehydrogenation. Almost 100% selectivity to cyclohexene could be obtained when the molar ratio of acetic acid to cyclohexane was 12.9:1 at 450 degrees C, the conversion of cyclohexane was 6.9%.

Application of modified Nafion membrane to the sulfur dioxide gas electrochemical sensor

The electrochemical SO2 sensor worked at the fixed potential and prepared with Nafion membrane as the solid electrolyte was studied. It v as observed that after Nafion membrane, was treated with H2SO4, the water-preserving ability of the membrane was increased. In turn, the performance of the sensor became stable. After lifetime test for 4 months, the performance of the sensor deceased slightly, Thus this kind of sensor may become a gas sensor for the practical application.

Preparation and gas sensitivity of octa-n-butoxy-2,3-naphthalocyanine copper(II) Langmuir-Blodgett film

The formation process of monolayer of octa-n-butoxy-2,3-naphthalocyanine copper ( I), [CuNc(OBu)(8)], on water subphase was studied. Its multilayers were successifully deposited on the hydrophilic substrates by Z-type deposition mode using LB technique. Stable solid film with a limiting molecular area of 0.74 nm(2) and a collapse pressure of 55 mN/m were formed. The LB film structure was characterized by IR and electronic absorption spectra. Macrocycle of CuNc (OBu)(8) molecules have a face-to-face arrangement in the multilayers. These films have good sensitivities to vapor of alcohols, with the following sequence of sensitivities: i-PrOH>EtOH>MeOH. The response time and recovery time of the LB films to vapor of MeOH, EtOH and i-PrOH[volume fraction (1-5) X 10(-5)] were within 2 and 5 seconds respectively, while those of the LB films to ammonia(1 X 10(-4)) were 30-60 seconds and 4-5 minutes respectively.

H/D exchange reaction of cyclopropane derivatives in the ion system of CD3OD

The fragmentation properties of the product ions [M + 1](+), [M + 2](+) and [M + 3](+) formed by ion-molecule reaction of four cyclopropane derivatives with the ion system of CD3OD were investigated by using collision-induced dissocation technique. The experiment results indicated that the product ions were produced via the H/D exchange reaction between reactants and reactive reagent ions of CD3OD. There are two exchangable hydrogen atoms on the ring of compounds 1 and 2, and only one for compound 3 and 4.

Sites of protonation and unimolecular fragmentation of protonated N-hydroxyphthalimide in the gas phase

The low energy collision-induced dissociation, linked scan techniques and isotopic labeling experiment were used to investigate the unimolecular fragmentation of protonated N-hydroxyphthalimide under electron impact and chemical ionization conditions. It was found that this compound shows an unusual reactivity towards protonation. Two possible sites of protonation have been proposed to explain the corresponding fragmentation processes, one is that the protonation takes place on the oxygen atom of hydroxyl group, resulting in the loss of water and the other is the formation of an intermediary proton-bound complex in the fragmentation process, giving rise to the fragment ions of m/z 133 and m/z 135. The results show both cases are coexistence in the fragmentations of protonated N-hydroxyphthalimide, and the unimolecular fragmentation pathways are available.

Structure of [C8H7](+) and intramolecular proton transfer reactions in 3-phenyl-1-butyn-3-ol by MS/MS technique

The electron impact mass spectrum (EIMS) of 3-phenyl-1-butyn-3-ol was reported in this paper. Collision-induced dissociation (CID) was used to study the gas phase ion structure of [C8H7](+) formed by the fragmentation of ionized 3-phenyl-1-butyn-3-ol, and that it has the same structure as m/z 103 ions generated by cinnamic acid and alpha-methylstyrene. Deuterium labelling, metastable ion (MI) and CID experimental results indicate the formation of m/z 103 ion resulting from molecular ion of 3-phenyl-1-butyn-3-ol, which is a stepwise procedure via twice proton transfers, rather than concerted process during the successive elimination of methyl radical and neutral carbon monoxide accompanying hydrogen transfer. Moreover, in order to rationalized these fragmentation processes, the bimolecular proton bound complex between benzyne and acetylene intermediate has been proposed.

The transfer of chloride ion across an anion exchange membrane

The transfer of chloride ions into a low resistance anion exchange membrane (AEM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectra. In all cases, concentration polarization of Cl- ions is exterior to the membrane. It controls the flux and produces the limiting currents: either steady state or transient (peak type) current. In CV experiments, when the size of the holes in the membrane was much smaller than the distance between membrane holes, the Cl- anion transfer showed steady state voltammetric behavior. Each hole in the membrane can be regarded as a microelectrode and the membrane was equivalent to a microelectrode array in this condition. When the hole in the membrane was large or the distance between membrane holes was small, the CV curve of the Cl- anion transfer across the membrane showed a peak shape, which was attributed to linear diffusion. In AC impedance measurement, the impedance spectrum of the membrane system was composed of two semicircles at low DC bias, corresponding to the bulk characteristics of the membrane and the kinetic process of ion transfer, respectively. The bulk membrane resistance increases with increasing DC bias and only one semicircle was observed at higher DC bias. The parameters related to kinetic and membrane properties were discussed.

Probe beam deflection study of the ion exchange between Prussian blue film or indium hexacyanoferrate film and electrolyte solutions

Probe beam deflection(PBD) technique together with electrochemical techniques such as cyclic voltammetry was used to study the ion exchange in prussian blue(PB) film and its analogue indium hexacyanoferrate (InHCF) chemically modified electrodes, The ion exchange mechanism of PB was verified as following: K2Fe2+FeI(CN)(6)(-e--K+)reversible arrow(+e-+K+)KFe(3+)Fe(I)(CN)(6)(-xe--xK+)reversible arrow(+xe-+xK+) [Fe3+FeI(CN)(6)](x)[KFe3+FeI(CN)(6)](1-x) where on reduction in contact with an acidic KCl electrolyte, H+ enter PB film before K+. Both the cations and anions participate concurrently in the redox process of InHCF, meanwhile K+ ion plays a major role in the whole charge transfer process of this film with increasing radii of anions.