Thermo-Chemo-Electro-Mechanical Formulation of Saturated Charged Porous Solids

A thermo-chemo-electro-mechanical formulation of quasi-static finite deformation of swelling incompressible porous media is derived from a mixture theory including the volume fraction concept. The model consists of an electrically charged porous solid saturated with an ionic solution. Incompressible deformation is assumed. The mixture as a whole is assumed locally electroneutral. Different constituents following different kinematic paths are defined: solid, fluid, anions, cations and neutral solutes. Balance laws are derived for each constituent and for the mixture as a whole. A Lagrangian form of the second law of thermodynamics for incompressible porous media is used to derive the constitutive restrictions of the medium. The material properties are shown to be contained in one strain energy function and a matrix of frictional tensors. A principle of reversibility results from the constitutive restrictions. Existing theories of swelling media should be evaluated with respect to this principle.     

Exact results for the Kardar-Parisi-Zhang equation with spatially correlated noise

We investigate the Kardar-Parisi-Zhang (KPZ) equation in d spatial dimensions with Gaussian spatially long-range correlated noise -- characterized by its second moment -- by means of dynamic field theory and the renormalization group. Using a stochastic Cole-Hopf transformation we derive exact exponents and scaling functions for the roughening transition and the smooth phase above the lower critical dimension . Below the lower critical dimension, there is a line marking the stability boundary between the short-range and long-range noise fixed points. For , the general structure of the renormalization-group equations fixes the values of the dynamic and roughness exponents exactly, whereas above , one has to rely on some perturbational techniques. We discuss the location of this stability boundary in light of the exact results derived in this paper, and from results known in the literature. In particular, we conjecture that there might be two qualitatively different strong-coupling phases above and below the lower critical dimension, respectively. Received 5 August 1998     

Possibilities and Limitations of Fast Temperature Programming as a Route towards Fast GC

One possible way to speed up a gas chromatographic analysis is the application of fast temperature programming by using resistive heating techniques. With this heating technique programming rates up to 20° per second can be reached. A relative standard deviation of retention times better than 0.2% is obtained. Using fast temperature programming the analysis-times of a mineral oil sample, an industrial oligomer sample, and toxic compounds in diesel fuel have been reduced 5 to 20 times, compared to a standard temperature programmed analysis. In most cases resistive heating cannot be applied to reduce the analysis time of a complex sample. The use of fast temperature programming is preferable to the use of short columns and columns operated at above-optimum carrier gas velocities.     

Sorption Tubes Packed with Polydimethylsiloxane: A New and Promising Technique for the Preconcentration of Volatiles and Semi-Volatiles from Air and Gaseous Samples

This paper is concerned with the determination of volatile and semi-volatile organic components in air and gaseous (headspace) samples, focusing primarily on polar analytes. Samples were analyzed by preconcentration on different (ad)sorbents followed by thermal desorption and analysis by capillary gas chromatography. The performance of a cartridge filled with 100% polydimethylsiloxane (PDMS) particles was compared to that of adsorbents like Tenax TA and Carbotrap 300. Though the PDMS phase is non-polar it showed adequate retention for both polar and non-polar components. The blank runs of the PDMS trap were significantly better than those of most adsorbents and did not deteriorate, as was the case with all the conventional adsorbents investigated. With respect to trapping efficiencies, the PDMS phase performed better for most of the analytes under investigation compared to the adsorbents. For a range of analytes including triethylamine, butanone, diacetyl, nicotine, and acetic acid the PDMS phase performed exceptionally well whereas all adsorbents showed unsatisfactory performance. The packed PDMS traps were employed for the determination of organic acids, PAH's and nitro-PAH's in air and for the analysis of the headspace of cacao and hop.     

Synthesis and characterization of new copolymers of thiophene and vinylene: Poly(thienylenevinylene)s and poly(terthienylenevinylene)s with thioether side chains

Poly[3,4-bis(3-methylbutylthio)thienylenevinylene], poly[3,4-bis-(S)-(2-methylbutylthio)thienylenevinylene], poly[3′,4′-bis(3-methylbutylthio)-2,2′:5′,2″-terthienylene-5,5″-vinylene], and poly{3′,4′-bis-(S)-[2-methylbutylthio]-2,2′:5′,2″-terthienylene-5,5″-vinylene} have been synthesized. The synthesis starts from the thiophene monomers and trimers, which are formylated to give the corresponding dialdehydes. The dialdehydes are reductively polymerized using a McMurry coupling. The polymers are characterized by GPC, optical spectroscopy (FT-IR, UV-vis, circular dichroism spectroscopy and photoluminescence) and by proton and carbon NMR spectroscopy. The polymers are soluble in common organic solvents, such as THF, chloroform, toluene, benzene and 1,2-dichlorobenzene. The solvatochromism and thermochromism of the polymers in solution are investigated, while the optical activity of the polymers is used to investigate the supramolecular aggregation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4629–4639, 1999     

Development and evaluation of an interface for coupled capillary supercritical fluid chromatography/magnetic sector mass spectrometry. Application to thermally unstable and high molecular mass compounds

An interface for coupling supercritical fluid chromatography to a magnetic sector mass spectrometer was developed and evaluated. The interface is based on direct introduction of the mobile phase, carbon dioxide, into the ion-source of the mass spectrometer. The SFC-MS system was optimized with respect to the signal-to-noise ratio. Under optimized conditions, the estimated detection limit for n-pentadecane is approximately 30 ppm. Spectra obtained in the electron-impact ionization mode show a very good similarity with library spectra. The performance of the SFC-MS system was evaluated by the analysis of a number of test mixtures. A sample containing several low molecular mass, thermally unstable compounds, which could neither be analyzed by GC-MS nor by LC-MS, was analyzed. Also for the analysis of high molecular mass compounds, the coupled system showed a good performance.     

A Missing Reaction Step in Dithiobenzoate-Mediated RAFT Polymerization

The debate on the mechanism of dithiobenzoate-mediated RAFT polymerization may be overcome by taking the so-called “missing step” reaction between a highly reactive propagating radical and the three-arm star-shaped product of the combination reaction of an intermediate RAFT radical and a propagating radical into account. The “missing step” reaction transforms a propagating radical and a not overly stable three-arm star species into a resonance-stabilized RAFT intermediate radical and a stable polymer molecule. The enormous driving force behind the “missing step” reaction is estimated via DFT calculations of reaction enthalpies and reaction free enthalpies.