Interaction forces between cellulose microspheres and ultrathin cellulose films monitored by colloidal probe microscopy-effect of wet strength agents

Colloidal probe microscopy was employed to study forces between cellulose surfaces upon addition of a series of cationic copolymers in aqueous solution, as model compounds for wet strength agents. The content of quaternary ammonium groups and primary amines was systematically varied in the cationic polymers, to distinguish between the importance of electrostatical and H-bonding effects. Cellulose microspheres were glued at the apex of tipless microfabricated cantilevers and used as colloidal probes. Ultra thin cellulose films and cellulose fibres were employed as model surfaces. The cellulose films of a thickness of about 5 nm were spin-coated from cellulose solution onto silicon substrates. The root-mean-square-roughness (RMS) was 0.3-0.8 nm. The cationic model polymers were compared to Servamine, a polymer employed as standard wet strength resin in papermaking industries. Force versus separation measurements showed a detailed picture of adhesion and contact breaking. Relatively strong adhesion of the order of 0.3 mJ/m(2) was observed with Servamine within a range of approximately 10 nm. At larger distances weak bond breaking and elastic chain pulling were identified. When approaching the surface one to two small jump-in's possibly related to strong binding of Servamine and subsequent attraction could be found in the case of Servamine. In contrast, all the model copolymers showed only a weak adhesion of 8-30 micro/m(2), i.e., an order of magnitude less than that of Servamine and subsequent elastic rupture domains. The contour length, persistence length and characteristic rupture distances were calculated by means of applying the WLC model. Measurements against cellulose fibres obtained from the production process proved the relevance of the model systems.     

High resolution applications of laser-induced breakdown spectroscopy for environmental and forensic applications

Laser-induced breakdown spectroscopy (LIBS) has been used in the elemental analysis for a variety of environmental samples and as a proof of concept for a host of forensic applications. In the first application, LIBS was used for the rapid detection of carbon from a number of different soil types. In this application, a major breakthrough was achieved by using a multivariate analytical approach that has brought us closer towards a “universal calibration curve”. In a second application, it has been demonstrated that LIBS in combination with multivariate analysis can be employed to analyze the chemical composition of annual tree growth rings and correlate them to external parameters such as changes in climate, forest fires, and disturbances involving human activity. The objectives of using this technology in fire scar determinations are: 1) To determine the characteristic spectra of wood exposed to forest fires and 2) To examine the viability of this technique for detecting fire occurrences in stems that did not develop fire scars. These examples demonstrate that LIBS-based techniques are inherently well suited for diverse environmental applications. LIBS was also applied to a variety of proof of concept forensic applications such as the analysis of cremains (human cremation remains) and elemental composition analysis of prosthetic implants.     

Multi-element speciation of metalloproteins in fish tissue using size-exclusion chromatography coupled "on-line" with ICP-isotope dilution-time-of-flight-mass spectrometry

An on-line isotope dilution (ID) method in combination with the coupling of size-exclusion high-performance liquid chromatography (SE-HPLC) to an axial inductively coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) was applied to the quantitative speciation of Cu, Zn and Cd in carp and eel cytosols. Quantitative information on the distribution of essential and toxic metals between the different molecular weight fractions in kidney cytosols of control and Cd exposed carp was obtained with species-unspecific spiking by post-column addition of the enriched isotopes 65Cu, 67Zn and 106Cd. The isotope ratios 63Cu/65Cu, 64Zn/67Zn and 114Cd/106Cd, were monitored by ICP-TOFMS in transient signal mode. The determination of the total cytosolic element concentration was performed by flow injection conventional nebulization ICP-TOFMS. Speciation differences were encountered between control and Cd-stressed carp, indicating that quantitative speciation studies might be useful for ecotoxicological and biomonitoring purposes. Application of this methodology to quantitation of metals associated with metallothioneins (MT) in European eel, sampled at three different sites in Flanders, Belgium was also addressed. A significant increase of the amount of Cd, Cu and Zn bound to hepatic MT was observed with the increase of the total metal and MT concentrations of hepatic eel tissue.     

Electrophilic aromatic chlorination and haloperoxidation of chloride catalyzed by polyfluorinated alcohols: a new manifestation of template catalysis

We have demonstrated that a polyfluorinated alcohol, 2,2,2-trifluoroethanol, solvent enables haloperoxidase type activity and the oxychlorination of arenes (benzene and its alkylated derivatives) without a metal catalyst. The polyfluorinated alcohol has a dual function; it catalyzes electrophilic chlorination of less reactive arenes by several orders of magnitude and oxidation of chloride at lower H+ concentrations. DFT calculations show that a complementary charge template in the transition state explains the catalysis of the electrophilic chlorination.     

Pyrolysis/CVAAS for the determination of mercury in solid environmental samples

Summary A CVAAS method is reported for the determination of mercury in solid environmental materials by pyrolysis and a two-stage amalgamation on gold. Interferences by pyrolysis products are eliminated by a purification section containing a catalytic converter and two specific adsorbers for organic substances. The detection limit of the method is 5 ppb for a 20-mg sample. The reproducibility highly depends on the homogeneity of the materials.

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Pyrolyse/Kaltdampf-Atomabsorption zur Hg-Bestimmung in festen Umweltproben

Zusammenfassung Ein Kaltdampf-Atomabsorptions-Verfahren zur Quecksilberbestimmung in festen Umweltproben durch Pyrolyse und Zwei-Schritt-Amalgamierung auf Gold wurde angegeben. Störungen durch Pyrolyseprodukte lassen sich durch eine Reinigungsvorrichtung beseitigen, die einen katalytischen Konverter und zwei spezifische Absorber für organische Substanzen enthält. Die Nachweisgrenze für eine 20-mg-Probe liegt bei 5 ppb. Die Reproduzierbarkeit der Ergebnisse ist weitgehend von der Homogenität des Materials abhängig.

     

The use of magnetic fields in vertical Bridgman/Gradient Freeze-type crystal growth

This paper outlines advanced vertical Bridgman/Gradient Freeze techniques with flow control using magnetic fields developed for the growth of semiconductor crystals. Low-temperature flow modelling, as well as laboratory-scaled crystal growth under the influence of rotating, travelling, and static magnetic fields are presented. Experimental and numerical flow modelling demonstrate the potential of the magnetic fields to establish a well-defined flow for tailoring heat and mass transfer in the melt during growth. The results of the growth experiments are discussed with a focus on the influence of a rotating field on the segregation of dopants, the influence of a travelling field on the temperature field and thermal stresses, and the potential of rotating and static fields for a stabilization of the melt flow.     

High‐Field Pulsed EPR Spectroscopy for the Speciation of the Reduced [PV2Mo10O40]6− Polyoxometalate Catalyst Used in Electron‐Transfer Oxidations

An in‐depth spectroscopic EPR investigation of a key intermediate, formally notated as [PV^IVV^VMo₁₀O₄₀]^6? and formed in known electron‐transfer and electron‐transfer/oxygen‐transfer reactions catalyzed by H₅PV₂Mo₁₀O₄₀, has been carried out. Pulsed EPR spectroscopy have been utilized: specifically, W‐band electron–electron double resonance (ELDOR)‐detected NMR and two‐dimensional (2D) hyperfine sub‐level correlation (HYSCORE) measurements, which resolved ⁹⁵Mo and ¹⁷O hyperfine interactions, and electron–nuclear double resonance (ENDOR), which gave the weak ⁵¹V and ³¹P interactions. In this way, two paramagnetic species related to [PV^IVV^VMo₁₀O₄₀]^6? were identified. The first species (30–35 %) has a vanadyl (VO²⁺)‐like EPR spectrum and is not situated within the polyoxometalate cluster. Here the VO²⁺ was suggested to be supported on the Keggin cluster and can be represented as an ion pair, [PV^VMo₁₀O₃₉]^8?[V^IVO²⁺]. This species originates from the parent H₅PV₂Mo₁₀O₄₀ in which the vanadium atoms are nearest neighbors and it is suggested that this isomer is more likely to be reactive in electron‐transfer/oxygen‐transfer reaction oxidation reactions. In the second (70–65 %) species, the V^IV remains embedded within the polyoxometalate framework and originates from reduction of distal H₅PV₂Mo₁₀O₄₀ isomers to yield an intact cluster, [PV^IVV^VMo₁₀O₄₀]^6?.     

Modelling of material and structural inhomogeneities in timber structures

The numerical simulation of timber structures by means of FEM has been an object of recent research. Most of the material models developed so far are based on idealized assumptions by disregarding inhomogeneities. Here, models to capture structural inhomogeneities in terms of branches and knots and the resulting deviation in grain course in a three-dimensional FE analysis are presented. Besides, naturally varying material properties referred to as material inhomogeneities have to be considered in the structural analysis. Due to the insufficient experimental data, the uncertainty model fuzziness is applied. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Titanium phosphonate porous materials constructed from dendritic tetraphosphonates

An organic-inorganic hybrid material, TPPhA-Ti, was constructed by non-hydrolytic condensation of a dendritic tetrakis-1,3,5,7-(4-phosphonatophenyl)adamantane precursor and titanium(IV) isopropoxide. One preparative pathway yielded insoluble materials with a Ti/P ratio of approximately 1 which was confirmed by a combination of FT-IR, TGA, and EDS measurements. N2 sorption experiments showed that TPPhA-Ti is a porous solid (micropores approximately 13 A; mesopores approximately 38 A) with a high surface area, approximately 550 m2 g(-1). The structure and morphology of the TPPhA-Ti as investigated by transmission and scanning electron microscopy showed a layered-type material. Additional X-ray diffraction data suggest a paracrystalline material; an optimization of possible molecular arrangements of TPPhA-Ti was simulated that was in agreement with the experimental data. A second preparative pathway yielded a Ti oxide-phosphonate with a Ti/P ratio of approximately 3.4. Both TEM and SEM revealed that hollow nanospheres were formed with diameters of approximately 180-300 nm.     

Molecularly smooth cellulose surfaces for adhesion studies

Cellulose is deposited on silicon wafer surfaces via spin coating from a solution of cellulose in dimethylacetamide (+7% lithium chloride). The resulting cellulose layers were analyzed by ellipsometry, AFM, FTIR, ICP-MS, X-ray reflectivity, and contact angle measurements. For cellulose concentrations below 0.07 wt% the wafer surfaces are covered with a network of cellulose fibrils. For concentrations between 0.07 and 0.5 wt%, closed films with thicknesses between 1.5 and approximately 10 nm are obtained. These films are molecularly smooth (rms roughness<2 nm). Higher concentrations result in thicker films with significantly rougher surfaces (rms roughness>2 nm). The cellulose layers were used to investigate cellulose/cellulose adhesion and their modification by polyelectrolytes. To this end the sticking behavior of cellulose beads was analyzed. It is demonstrated that the sticking of the beads depends on the type, amount, and adsorption symmetry of adsorbed polyelectrolyte. Low, incomplete polyelectrolyte coverage always enhances sticking, whereas for high coverage the symmetry of the polyelectrolyte coating is very important. In this case, sticking (adhesion) is enhanced if only one surface is covered with polyelectrolyte prior to contact. If both surfaces were fully covered with polyelectrolytes before contact, sticking (adhesion) is decreased.