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.     

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.     

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.     

Directed synthesis of stable large polyoxomolybdate spheres

Polyoxometalates or POMs, a class of inorganic transition metal-oxide based clusters, have gained significant interest owing to their catalytic, magnetic, and material science applications. All such applications require high surface area POM based materials. However, chemically synthesized POMs are still at most in the range of a few nanometers, with their size and morphology being difficult to control. Hence, there is an immediate need to develop design principles that allow easy control of POM morphology and size on mesoscopic (50-500 nm) length scales. Here, we report a design strategy to meet this need. Our method reported here avoids a complex chemical labyrinth by using a prefabricated cationic 1,2-dioleol-3-trimethylammonium-propane (DOTAP) vesicle as a scaffold/structure directing agent and gluing simple anionic heptamolybdates by electrostatic interaction and hydrogen bonds to form large POM spheres. By this method, complexity in the resulting structure can be deliberately induced either via the scaffold or via the oxometalate. The high degree of control in the matter of the size and morphology of the resulting POM superstructures renders this method attractive from a synthetic standpoint.