Control of the biofouling bryozoan, Plumatella repens , using pulsed chlorine treatment

Bryozoans are common biofoulers of under-drain filter nozzles in rapid gravity filters in water treatment works. A potential method for controlling bryozoan biofouling is the use of chlorine in backwash water. Repeatedly exposing bryozoan colonies with chlorine for 20 min every 24 h in an experimental setting, to replicate what would occur if the backwash was chlorinated, caused significant reduction in colony growth and size. After 10 days repeated treatment in good conditions for bryozoan propagation, the EC50 (the chlorine concentration required to decrease growth such that treated colonies were half the size of control colonies) was 1.6 ppm (SE 0.3). In sub-optimal conditions for propagation, the impact of chlorine was greater. The majority of colonies treated with 1 ppm and above did not grow or even decreased in size over 5 days. However, a chlorine concentration of 5 ppm was necessary, even in sub-optimal conditions, to ensure all colonies decreased in size over 5 days of treatment; this is too high to be acceptable to water companies due to the risk of carcinogenic by-products. Nevertheless, the observed decline in feeding activity of bryozoans exposed to chlorine levels >1 ppm suggests that repeated backwashing with chlorine may cause colony death over time, especially in sub-optimal conditions. Chlorine backwashes may therefore be an effective long-term control strategy, especially in locations such as rapid gravity filters where it is suggested that upstream processes are likely to create sub-optimal conditions for bryozoan growth

SAXS observation of RCM1 under cyclical shear

A cylinder forming poly(styrene-b-butadiene-b-styrene) triblock copolymer melt is cyclically processed through a capillary at a high shear rate in the Cambridge Multipass Rheometer (MPR). In situ X-ray diffraction experiments enable observation of the effect of the shear on the block copolymer (BCP) nanophase orientation, both during and after processing. Temporal resolution of the X-ray exposures is increased, whilst retaining intensity, by exploiting the cyclical nature of the shear and the material's response to it; short exposures from many cycles, individually having few counts, are added together to produce well resolved X-ray patterns. Orientation of the cylinders reduces during processing, then increases during pauses between processing. The loss of orientation is attributed to the high shear rate deforming the melt faster than the structure can respond, whilst it is believed that melt relaxation, linked to the compressibility of the material, produces much lower shear rates after mechanical processing has ceased, which induces strong orientation of the nanostructure

Engineering orientation in block copolymers for application to prosthetic heart valves

This study demonstrates how the mechanical performance of polymeric material can be enhanced by morphology and phase orientation of block copolymers to achieve desired anisotropic mechanical properties. The material used was a new Kraton block copolymer consisting of styrene-isoprene-butadiene-styrene blocks having cylindrical morphology. We report a method of achieving long range uniaxial as well as biaxial orientation of block copolymer. Each microstructural organization results in a specific mechanical performance, which depends on the direction of the applied deformation. The method of tailoring mechanical properties by engineering microstructure may be successfully utilized to applications requiring anisotropic mechanical response, such as prosthetic heart valves

A SAXS study of flow alignment of thermotropic liquid crystal mixtures

We report on the capillary flow behaviour of thermotropic liquid crystal mixtures containing 4-n-octyl-4'-cyanobiphenyl (8CB) and 4-n-pentyl-4'-cyanobiphenyl (5CB). The liquid crystal mixtures are studied in the Nematic (N) and Smectic (SA) phases at room temperature. Polarised optical microscopy (POM), rheology and simultaneous X-ray diffraction (XRD)/capillary flow experiments are performed to characterise the system. Polarised optical microscopy reveals a dramatic change in optical texture when the 5CB content is increased from 20 to 30% in the mixtures. X-ray diffraction results show that the system goes through a SA-N phase transition, such that the mixtures are smectic for 10-20% 5CB and nematic for 30-90% 5CB. Smectic mixtures flow with the layers aligned along the flow direction (mesogens perpendicular to flow) while nematic mixtures flow with the mesogens aligned in the flow direction. Simultaneous XRD/shear flow experiments show that the SA-N transition is independent of the flow rate in the range 1-6 ml min-1. The correlation length of the liquid crystal order decreases with increasing 5CB content. Rheology is used to prove that the correlation length behaviour is related to a reduction in the viscosity of the mixture

In Situ controlled promotion of catalyst surfaces via NEMCA: the effect of Na on the Pt-catalyzed CO oxidation

Summarization: It was found that the catalytic activity of Pt for CO oxidation can be markedly and reversibly affected by depositing polycrystalline Pt films on β″-Al2O3, a Na+ conductor, and applying external potentials to supply or remove Na to or from the Pt catalyst surface. The change in the rate of CO oxidation is typically 103-105 times larger than the rate of supply or removal of Na. The use of the β″-Al2O3 solid electrolyte supports permits precise in situ control of the Na coverage on the Pt surface. Sodium coverages of 0.02 cause up to 600% steady-state increase in the rate of CO oxidation under CO-rich conditions. The promoting effect is due to enhanced oxygen chemisorption on the Pt surface. Higher (>0.06) Na coverages poison the rate severely and reversibly due to the formation of a CONaPt surface complex. Rate oscillations can be reversibly induced or stopped and their frequency can be controlled by controlling the catalyst potential VWR and average work function eφ.Presented on: Journal of Catalysi