Interfacial properties of colloid-polymer mixtures

Density functional theory and a virial approach are used to calculate the surface tension and bending rigidity of the interface between demixed fluid phases for a colloid-polymer mixture. The calculated surface tension compares well with results from computers simulations and experiments. The bending rigidity obtained from both theoretical approaches is negative (approximately equal to -0.1k(B)T), its magnitude increases away from the critical point and it is in reasonable agreement with computer simulations.     

Characterization of a microelectromechanical systems-based counter-current flame ionization detector

This work is concerned with the influence of different operating parameters on the response of a counter-current micro flame ionization detector (cc-μFID) with low gas consumption for mobile applications. At cc-μFID flow rates (<10ml/min hydrogen), the response depends mainly on the oxygen flow. At 7.5ml/min hydrogen flow, highest sensitivity (13.7mC/gC) is obtained with the smallest flame chamber and nozzle size, moderate sample gas flow (2.0ml/min), and an oxygen flow above stoichiometry (9.4ml/min, λ=2.5). The largest absolute signal is obtained at increased sample gas flow (8.0ml/min). However, to prevent parting of the micro-flame by the sample gas stream, largest nozzles (smallest outflow velocity) give the best result (4.37nA). Whereas cc-μFID sensitivity is comparable with conventional FID sensitivity, peak-to-peak noise of 1pA is relatively large. Therefore, the minimum detectable carbon mass flow of 1.46×10(-10)gC/s and the minimum detectable methane concentration of 3.43ppm are larger than typical FID detection limits. μGC-μFID experiments show the difference between premixing the sample with the hydrogen or with the oxygen with respect to sensitivity and response factors. Sensitivity is decreased considerably when the column effluent is added to the oxygen instead of to the hydrogen. For hydrogen premixed samples the response factor to butane can be increased up to 0.81 (methane=1), whereas for oxygen premixed samples it is maximally 0.31. This smaller sensitivity to oxygen premixed samples and the larger variation of response factors shows the importance of the hydrogen atom during breakdown of organic molecules to single-carbon fragments before ionization.     

Biosupramolecular nanowires from chlorophyll dyes with exceptional charge-transport properties

Conductive tubes: Self-assembled nanotubes of a bacteriochlorophyll derivative are reminiscent of natural chlorosomal light-harvesting assemblies. After deposition on a substrate that consists of a non-conductive silicon oxide surface (see picture, brown) and contacting the chlorin nanowires to a conductive polymer (yellow), they show exceptional charge-transport properties.     

Selective Modification of Ribosomally Synthesized and Post-Translationally Modified Peptides (RiPPs) through Diels–Alder Cycloadditions on Dehydroalanine Residues

We report the late-stage chemical modification of ribosomally synthesized and post-translationally modified peptides (RIPPs) by Diels–Alder cycloadditions to naturally occurring dehydroalanines. The tail region of the thiopeptide thiostrepton could be modified selectively and efficiently under microwave heating and transition-metal-free conditions. The Diels–Alder adducts were isolated and the different site- and endo/exo isomers were identified by 1D/2D ¹H NMR. Via efficient modification of the thiopeptide nosiheptide and the lanthipeptide nisin Z the generality of the method was established. Minimum inhibitory concentration (MIC) assays of the purified thiostrepton Diels–Alder products against thiostrepton-susceptible strains displayed high activities comparable to that of native thiostrepton. These Diels–Alder products were also subjected successfully to inverse-electron-demand Diels–Alder reactions with a variety of functionalized tetrazines, demonstrating the utility of this method for labeling of RiPPs.     

Influence of liquid layers on energy absorption during particle impact

The influence of the thickness of a covering liquid layer and its viscosity as well as the impact velocity on energy loss during the normal impact on a flat steel wall of spherical granules with a liquid layer was studied. Free-fall experiments were performed to obtain the restitution coefficient of elastic-plastic γ- Al2O3 granules by impact on the liquid layer, using aqueous solutions of hydroxypropyl methylcellulose with different concentrations for variation of viscosity （1-300 mPa s）, In the presence of a liquid layer, increase of liquid viscosity decreases the restitution coefficient and the minimum thickness of the liquid layer at which the granule sticks to the wall. The measured restitution coefficients were compared with experiments performed without liquid layer. In contrast to the dry restitution coefficient, due to viscous losses at lower impact velocity, higher energy dissipation was obtained, A rational explanation for the effects obtained was given by results of numerically solved force and energy balances for a granule impact on a liquid layer on the wall. The model takes into account forces acting on the granule including viscous, surface tension, capillary, contact, drag, buoyancy and gravitational forces. Good agreement between simulations and experiments has been achieved.     

Gas–solid interaction force from direct numerical simulation (DNS) of binary systems with extreme diameter ratios

Fluid–particle systems as commonly encountered in chemical, metallurgical and petroleum industries are mostly polydisperse in nature. However, the relations used to describe fluid–particle interactions are originally derived from monodisperse systems, with ad hoc modifications to account for polydispersity. In previous work it was shown that for bidisperse systems with moderate diameter ratios of 1:2 to 1:4, this approach leads to discrepancies, and a correction factor is needed. In this work we demonstrate that this correction factor also holds for more extreme diameter ratios of 1:5, 1:7 and 1:10, although the force on the large particles is slightly overestimated when using the correction factor. The main origin of the correction is that the void surrounding the large particles becomes less in case of a bidisperse mixture, as compared to a monodisperse system with the same volume fraction. We further investigated this discrepancy by calculating the volume per particle by means of Voronoi tessellation.     

Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulklike fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations.     

Soft-landing deposition of radioactive probe atoms on surfaces

We present a method to deposit a wide range of radioactive probe atoms on surfaces, without introducing lattice damage or contaminating the surface with other elements or isotopes. In this method, the probe atoms are mass-separated using an isotope separator, decelerated to 5 eV, and directly deposited on the surface. The method allows for performing hyperfine interactions experiments using trace amounts of radioactive probes located at surfaces and interfaces. The characteristics of the deposition method will be described, with particular attention to the deceleration stage of the isotope separator. The method was tested with perturbed angular correlation (PAC) experiments on the system In on Cu(17,1,1). The results are in agreement with molecular dynamics simulations of the deposition process. New developments, in particular the study of the self-diffusion of Ag atoms on Ag(100) by means of PAC with the ¹¹¹Ag probe, are briefly discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation of synthetic phospholipid ultrasound contrast agents

The echogenic properties of synthetic, phospholipid encapsulated, air-filled microbubbles with various carbon-chain length as ultrasound contrast agents are investigated through the use of a flow-through laboratory ultrasound system. Specifically, we investigate the effect of shell carbon-chain length on the ultrasonic signal for a variety of flow rates. Averaged, integrated backscatter power measurements from the lipid encapsulated agents are benchmarked against those of Albunex (Albunex is a registered trademark of Molecular Biosystems, Inc., San Diego, CA), a commercially available, air-filled protein microbubbles contrast agent, approved for clinical use in echocardiography in the United States by the Food and Drug Administration. We find that the lipid encapsulated agents sustain less damage leading to gas dissolution or particle destruction as compared to Albunex in the slow-flow studies performed. The carbon-chain length of the encapsulating lipid molecule is shown not to observably affect the backscattered amplitude of ultrasound at flow velocities exceeding 7 mm/s.     

Strength and stiffness of a reinforced flexible hose

Flexible hoses, consisting of a rubber tube reinforced by one or more cylindrical braids composed of thin steel wires, are frequently used in hydraulics. They need to be both capable of withstanding high pressures, and rather flexible, two more or less contradictory requirements. In this paper we consider a straight tube with only one steel braid. We calculate stresses and strains resulting from an internal pressure using three models of a tube. Two of these are membrane models, one with elastic steel fibres and the other with inextensible wires. The third one is a thick-walled tube model. In particular, we pay attention to the effect of the so-called neutral angle of the wires. Part of the analysis is non-linear. However, the ultimate numerical evaluation pertains to a linearized theory, i.e. the deformations are small.