Exceptional function of nanoporous metal organic framework particles in emulsion stabilisation

A new concept of nanoporous metal organic framework particles stabilising emulsions was investigated. The copper benzenetricarboxylate MOF particles adsorbed at the oil/water interface play an exceptional role in stabilising both oil-in-water and water-in-oil emulsions. © 2013 The Royal Society of Chemistry.

Active stabilisation of single drive dual-parallel Mach-Zehnder modulator for single sideband signal generation

Presented is a study on a single-drive dual-parallel Mach-Zehnder modulator implementation as a single sideband suppressed carrier generator. High values of both extinction ratio and sidemode suppression ratio were obtained at different modulation frequencies over the Cband. In addition, a stabilisation loop had been developed to preserve the single sideband generation over time. © The Institution of Engineering and Technology 2013.

Oxidative degradation and stabilisation of polymers

The aim of this review is to present a coherent treatment of the fundamental aspects of the science that underpins current technological practices, and future advances, in the stabilisation of synthetic organic polymers. Aspects of polymer oxidation are introduced first before discussing the role of antioxidants, with numerous examples, to illustrate their basic mechanisms of action. The state of the art is discussed with particular emphasis on recent development and progress.

Perspectives in stabilisation of polyolefins

Polyolefins, which normally undergo high temperature manufacturing and fabrication operations, are susceptible to oxidation during each stage of their lifecycle. Stabilisers and antioxidants are used to inhibit the oxidative damage that is ultimately responsible for loss of physical properties, embrittlement and premature failure. Environmental awareness and health and safety considerations have spurred intense searches for new approaches to procure improved, safe, and more efficient antioxidants and stabiliser systems for polymers. Current activities have concentrated on two approaches: the first advocates the use of biological (naturally occurring) antioxidants, and the second relies on the use of reactive antioxidants that are chemically attached onto the polymer backbone for greater permanence and safety. Stabilisation of polyolefins through the use of vitamin E and some reactive, non-migratory antioxidants is the subject matter of this chapter.

Role of transglutaminase 1 in stabilisation of intercellular junctions of the vascular endothelium

Microvascular endothelial monolayers from mouse myocardium (MyEnd) cultured for up to 5 days postconfluency became increasingly resistant to various barrier-compromising stimuli such as low extracellular Ca2+ and treatment with the Ca2+ ionophore A23187 and with the actin depolymerising compound cytochalasin D. In contrast, microvascular endothelial monolayers from mouse lung microvessels (PulmEnd) remained sensitive to these conditions during the entire culture period which corresponds to the well-known in vivo sensitivity of the lung microvasculature to Ca2+depletion and cytochalasin D treatment. One molecular difference between pulmonary and myocardial endothelial cells was found to be transglutaminase 1 (TGase1) which is strongly expressed in myocardial endothelial cells but is absent from pulmonary endothelial cells. Resistance of MyEnd cells to barrier-breaking conditions correlated strongly with translocation of TGase1 to intercellular junctions. Simultaneous inhibition of intracellular and extracellular TGase activity by monodansylcadaverine (MDC) strongly weakened barrier properties of MyEnd monolayers, whereas inhibition of extracellular TGases by the membrane-impermeable active site-directed TGase inhibitor R281 did not reduce barrier properties. Weakening of barrier properties could be also induced in MyEnd cells by downregulation of TGase1 expression using RNAi-based gene silencing. These findings suggest that crosslinking activity of intracellular TGase1 at intercellular junctions may play a role in controlling barrier properties of endothelial monolayers.

Involvement of tissue transglutaminase in the stabilisation of biomaterial/tissue interfaces important in medical devices

Tissue transglutaminase (tTG) has recently been established as a novel cell surface adhesion protein that binds with high affinity to fibronectin in the pericellular matrix. In this study, we have made use of this property to enhance the biocompatibility of poly(epsilon-caprolactone) (PCL), a biomaterial currently used in bone repair. Poly(epsilon-caprolactone) discs were first coated with fibronectin and then tTG. The surface localisation of the two proteins was confirmed using ELISA and the tTG shown to be active on the surface by incorporation of biotin cadaverine into the fibronectin coating. When human osteoblasts (HOBs) were seeded onto the coated polymer surfaces in serum free medium, the surface coated with fibronectin and then tTG showed an increase in the spreading of the cells as compared to the surface coated with fibronectin alone, when analysed using environmental scanning electron microscopy. The presence of tTG had no effect on HOB cell differentiation when analysed by determining alkaline phosphatase activity. The use of tTG as a novel adhesion protein in this way may therefore have considerable potential in forming a stable tissue/biomaterial interface for application in medical devices.

Learning from mother nature:exploiting a biological antioxidant for the melt stabilisation of polymers

An overview of the antioxidant role of the biologically active form of vitamin E, α-tocopherol, in polyolefins is discussed. The effect of the vitamin antioxidant on the melt and colour stability of polyethylene (PE) and polypropylene (PP) is highlighted. It is shown that tocopherol is a highly effective antioxidant that results in superior melt stabilisation of polyolefins particularly when used at much lower concentration than that needed for conventional synthetic hindered phenol processing stabilisers. As with other hindered phenols,α-tocopherol imparts also some colour to the polymer but this is shown to be reduced drastically in the presence of other antioxidants, such as phosphites, or other additives, such as polyhydric alcohols.

Low frequency dielectric spectroscopy of bitumen binders as an indicator of adhesion potential to quartz aggregates using Portland cement

The purpose of this investigation was to interpret the bitumen-aggregate adhesion based on the dielectric spectroscopic response of individual material components utilizing their dielectric constants, refractive indices and average tangent of the dielectric loss angle (average loss tangent). Dielectric spectroscopy of bitumen binders at room temperature was performed in the frequency range of 0.01–1000 Hz. Dielectric spectroscopy is an experimental method for characterizing the dielectric permittivity of a material as a function of frequency. Adhesion data has been determined using the Rolling bottle method. The results show that the magnitude of the average tangent of the dielectric loss angle (average loss tangent) depends on bitumen type. The average loss tangent in the frequency range 0.01–1 Hz is introduced as a potential indicator for predicting polarizability and, thereby, adhesion potential of bitumen binders to quartz aggregates when using Portland cement. In order to obtain acceptable adhesion of 70/100 penetration grade bitumen binders and quartz aggregates when using Portland cement, it is suggested that the binder have an average tan δ > 0.035 in the frequency range 0.01–1 Hz.

Stabilisation and characterisation of peroxide-crosslinked high density polyethylene

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CO-stabilisation mechanisms of nanoparticles and surfactants in Pickering emulsions produced by membrane emulsification

Two different membrane emulsification methods were used to study mechanisms for co-stabilisation of emulsions, by either electrostatic or steric stabilised nanoparticles with anionic, cationic or non-ionic surfactants. The experimental results demonstrated the existence of two distinct co-stabilisation mechanisms that arise from interactions of the nanoparticles and surfactant molecules. When significant interaction is not involved, independent competitive adsorption of nanoparticles and surfactant molecules occurs spontaneously to stabilise droplets in formation. The adsorption/desorption equilibrium between surfactant molecules determines the longevity of the droplet stability. When the surfactant molecule reacts with the nanoparticle surface, the resultant surface modification appears to generate faster wetting kinetics for nanoparticles at the oil/water interface and yields enhanced stabilisation. The paper discusses the implications of controlling these interactions for emulsion production membrane systems.

Thermal stability of porous sol-gel phosphosilicates and their surface area stabilisation by lanthanum addition

The thermal stability of porous sol-gel phosphosilicates was studied by comparing the textural features upon calcination between 400 and 550 °C. A significant loss of surface area and pore volume were observed; the first is due to thermal coarsening of the nanoparticles, and the pore volume reduction was ascribed to sintering of the most external nanoparticles producing less void volume. Lanthanum addition was investigated as thermal stabilizer. For the mesoporous phosphosilicate composition, lanthanum addition enhanced the surface area, showing a 45% and 50% improvement with respect to the La-free counterpart; the effect was much less visible for the macroporous composition.