Experimental study of efficient mixing in a micro-fluidized bed

Micro-fluidized beds represent a novel means of significantly enhancing mixing and mass and heat transfer under the low Reynolds number flows that dominate in microfluidic devices. This study experimentally evaluates the mixing performance of a micro-fluidized bed and the improvements it affords over the equivalent particle-free system. The dye dilution technique coupled with standard top-view image analysis was used to characterize the mixing in a 400×175μm 2 polydimethylsiloxane (PDMS) Y-microchannel. Overall, the micro-fluidized bed provided a mixing effectiveness and energetic efficiency of mixing that were up to three times greater than those of a particle-free channel of the same dimensions. The mixing performance is strongly affected by specific power input and bed voidage. The optimal operating voidage, which corresponds to the energetic efficiency of mixing being maximal, is around 0.77 for the smallest particle-to-channel size ratio considered here 0.121, and appears to increase beyond this with size ratio

Molecular-level understanding of protein adsorption at the interface between water and a strongly interacting uncharged solid surface

Although protein adsorption on solids is of immense relevance, experimental limitations mean there is still a remarkable lack of understanding of the adsorption mechanism, particularly at a molecular level. By subjecting 240+ molecular dynamics simulations of two peptide/water/solid surface systems to statistical analysis, a generalized molecular level mechanism for peptide adsorption has been identified for uncharged surfaces that interact strongly with the solution phase. This mechanism is composed of three phases: (1) biased diffusion of the peptide from the bulk phase toward the surface; (2) anchoring of the peptide to the water/solid interface via interaction of a hydrophilic group with the water adjacent to the surface or a strongly interacting hydrophobic group with the surface; and (3) lockdown of the peptide on the surface via a slow, stepwise and largely sequential adsorption of its residues, which we term 'statistical zippering'. The adsorption mechanism is dictated by the existence of water layers adjacent to the solid and orientational ordering therein. By extending the solid into the solution by ∼8 Å and endowing it with a charged character, the water layers ensure the peptide feels the effect of the solid at a range well beyond the dispersion force that arises from it, thus inducing biased diffusion from afar. The charging of the interface also facilitates anchoring of the peptide near the surface via one of its hydrophilic groups, allowing it time it would otherwise not have to rearrange and lockdown. Finally, the slowness of the lockdown process is dictated by the need for the peptide groups to replace adjacent tightly bound interfacial water. © 2014 American Chemical Society

Modelling of immiscible liquid-liquid systems by Smoothed Particle Hydrodynamics

Immiscible fluid systems are ubiquitous in industry, medicine and nature. Understanding the phase morphologies and intraphase fluid motion is often desirable in many of these situations; for example, this will aid improved design of microfluidic platforms for the production of medicinal formulations. In this paper, we detail a Smoothed Particle Hydrodynamics (SPH) approach that facilitates this understanding. The approach includes surface tension and enforces incompressibility. The approach also allows the consideration of an arbitrary number of immiscible phases of differing viscosities and densities. The nature of the phase morphologies can be arbitrary and change in time, including break-up (which is illustrated) and coalescence. The use of different fluid constitutive models, including non-Newtonian models, is also possible. The validity of the model is demonstrated by applying it to a range of model problems with known solutions, including the Young-Laplace problem, confined droplet deformation under a linear shear field, and a droplet falling under gravity through another quiescent liquid. Results are also presented to illustrate how the SPH model can be used to elucidate the behaviour of immiscible liquid systems

Comparison of RAFT derived poly(vinylpyrolidone) verses Poly(oligoethyleneglycol methacrylate) for the stabilization of glycosylated gold nanoparticles

Carbohydrates dictate many biological processes including infection by pathogens. Glycosylated polymers and nanomaterials which have increased affinity due to the cluster glycoside effect, are therefore useful tools to probe function, but also as prophylactic therapies or diagnostic tools. Here, the effect of polymer structure on the coating of gold nanoparticles is studied in the context of grafting density, buffer stability and in a lectin binding assay. RAFT polymerization is used to generate poly(oligoethyleneglycol methacrylates) and poly(N-vinyl pyrolidones) with a thiol end-group for subsequent immobilization onto the gold. It is observed that poly(oligoethylene glycol methacrylates), despite being widely used particle coatings, lead to low grafting densities which in turn resulted in lower stability in biological buffers. A depression of the cloud point upon nanoparticle immobilization is also seen, which might compromise performance. In comparison poly(vinyl pyrolidones) resulted in stable particles with higher grafting densities due to the compact size of each monomer unit. The higher grafting density also enabled an increase in the number of carbohydrates which can be installed per nanoparticle at the chain ends, and gave increased binding in a lectin recognition assay. These results will guide the development of new nanoparticle biosensors with enhanced specificity, affinity and stabilit

A new VLA/e-MERLIN limit on central images in the gravitational lens system CLASS B1030+074

We present new VLA 22-GHz and e-MERLIN 5-GHz observations of CLASS B1030+074, a two-image strong gravitational lens system whose background source is a compact flat-spectrum radio quasar. In such systems we expect a third image of the background source to form close to the centre of the lensing galaxy. The existence and brightness of such images is important for investigation of the central mass distributions of lensing galaxies, but only one secure detection has been made so far in a galaxy-scale lens system. The noise levels achieved in our new B1030+074 images reach 3 microJy/beam and represent an improvement in central image constraints of nearly an order of magnitude over previous work, with correspondingly better resulting limits on the shape of the central mass profile of the lensing galaxy. Simple models with an isothermal outer power law slope now require either the influence of a central supermassive black hole, or an inner power law slope very close to isothermal, in order to suppress the central image below our detection limit. Using the central mass profiles inferred from light distributions in Virgo galaxies, moved to z=0.5, and matching to the observed Einstein radius, we now find that 45% of such mass profiles should give observable central images, 10% should give central images with a flux density still below our limit, and the remaining systems have extreme demagnification produced by the central SMBH. Further observations of similar objects will therefore allow proper statistical constraints to be placed on the central properties of elliptical galaxies at high redshift.Comment: Accepted by Monthly Notices of the Royal Astronomical Society. 16 pages, 8 figure

Solution processed graphene structures for perovskite solar cells

Organometallic trihalide perovskite light absorber based solar cells have drawn increasing attention because of their recent rapid increase in power conversion efficiency (PCE). These photovoltaic cells have relied significantly on transparent conducting oxide (TCO) electrodes which are costly and brittle. Herein, solution processed transparent conductive graphene films (TCGFs) are utilized, for the first time, as an alternative to traditional TCO electrodes at the electron collecting layer in perovskite solar cells (PSCs). By investigating and optimizing the trade-off between transparency and sheet resistance (Rs) of the graphene films, a PCE of 0.62% is achieved. This PCE is further improved to 0.81% by incorporating graphene structures into both compact and mesoporous TiO2 layers of the solar cell. We anticipate that the present study will lead to further work to develop graphene-based transparent conductive electrodes for future solar cell devices

A new method for reconstruction of the structure of micro-packed beds of spherical particles from desktop X-ray microtomography images. Part A. Initial structure generation and porosity determination

Micro-packed beds (μPBs) are seeing increasing use in the process intensification context (e.g. micro-reactors), in separation and purification, particularly in the pharmaceutical and bio-products sectors, and in analytical chemistry. The structure of the stationary phase and of the void space it defines in such columns is of interest because it strongly influences performance. However, instrumental limitations - in particular the limited resolution of various imaging techniques relative to the particle and void space dimensions - have impeded experimental study of the structure of μPBs. We report here a new method that obviates this issue when the μPBs are composed of particles that may be approximated by monodisperse spheres. It achieves this by identifying in successive cross-sectional images of the bed, the approximate centre and diameter of the particle cross-sections, replacing them with circles, and then assembling them to form the particles by identifying correlations between the successive images. Two important novel aspects of the method proposed here are: it does not require specification of a threshold for binarizing the images, and it preserves the underlying spherical geometry of the packing. The new method is demonstrated through its application to a packing of a near-monodispersed 30.5 μm particles of high sphericity within a 200 μm square cross-section column imaged using a machine capable of 2.28 μm resolution. The porosity obtained was, within statistical uncertainty, the same as that determined via a direct method whilst use of a commonly used automatic thresholding technique yielded a result that was nearly 10% adrift, well beyond the experimental uncertainty. Extension of the method to packings of spherical particles that are less monodisperse or of different regular shapes (e.g. ellipsoids) is also discussed

The effects of activated carbon surface features on the reactive adsorption of carbamazepine and sulfamethoxazole

© 2014 Elsevier Ltd. All rights reserved.Two commercial carbons, coconut shell- and wood-based were chosen to evaluate the mechanisms of carbamazepine (CBZ) and sulfamethoxazole (SMX) adsorption from a low (ppm level) concentration of these pharmaceuticals. The initial sample and those after adsorption were extensively characterized using potentiometric titration, thermal analysis combined with mass spectroscopy, FTIR, and XPS. It was found that not only porosity but also surface chemistry plays an important role in the adsorption process. The results show that extensive surface reactions take place during adsorption and adsorbates undergo significant transformations in the pore system. The ability of carbon surfaces to form superoxide ions results in the oxidation of CBZ and SMX, and their partial decomposition. Surface chemistry also promotes dimerization of the latter species. Moreover, functional groups of CBZ and SMX, mainly amines, react with oxygen groups of the carbon surface. Thus not only microporous carbons with sizes of pores similar to those of adsorbate molecules, but the carbons with large pores, rich in oxygen groups, can efficiently remove these pharmaceuticals following the reactive adsorption mechanism

Free-standing compact cathodes for high volumetric and gravimetric capacity Li–S batteries

Free-standing high performance Li–S battery cathodes are currently attracting significant research efforts. Loose macroporous structures have been proposed by many to improve sulfur utilization and areal capacity. However, their low cathode sulfur densities and high electrolyte fractions lead to low cell volumetric and gravimetric capacities. We report here a compact free-standing Li–S cathode structure that delivers areal, volumetric and gravimetric capacities all exceeding those of typical Li-ion batteries. The cathodes, formed by pressure filtration of the constituents, are composed of highly micro/mesoporous nitrogen-doped carbon nanospheres (NCNSs) embedded in the macropores of a multi-walled carbon nanotube (MWCNT) network to form a dense structure. The MWCNT network facilitates low cathode impedance. The NCNSs maximize sulfur utilization and immobilization. These collectively result in high cathode volumetric capacity (1106 mA h cm−3) and low electrolyte requirement (6 μL mg−1 of sulfur), which together lead to high cell-level gravimetric capacity. Stable long-term cycling at 0.3C (2.5 mA cm−2 for 5 mg cm−2 areal sulfur-loading) has also been achieved, with the areal and volumetric capacities of the best remaining above typical Li-ion values over 270 cycles and the per-cycle capacity fading being only 0.1%. The facile preparation means significant potential for large scale use.CH acknowledges a Postdoctoral Fellowship provided by Loughborough University