Magnetorheology in an aging, yield stress matrix fluid

Field-induced static and dynamic yield stresses are explored for magnetorheological (MR) suspensions in an aging, yield stress matrix fluid composed of an aqueous dispersion of Laponite® clay. Using a custom-built magnetorheometry fixture, the MR response is studied for magnetic field strengths up to 1 T and magnetic particle concentrations up to 30 v%. The yield stress of the matrix fluid, which serves to inhibit sedimentation of dispersed carbonyl iron magnetic microparticles, is found to have a negligible effect on the field-induced static yield stress for sufficient applied fields, and good agreement is observed between field-induced static and dynamic yield stresses for all but the lowest field strengths and particle concentrations. These results, which generally imply a dominance of inter-particle dipolar interactions over the matrix fluid yield stress, are analyzed by considering a dimensionless magnetic yield parameter that quantifies the balance of stresses on particles. By characterizing the applied magnetic field in terms of the average particle magnetization, a rheological master curve is generated for the field-induced static yield stress that indicates a concentration–magnetization superposition. The results presented herein will provide guidance to formulators of MR fluids and designers of MR devices who require a field-induced static yield stress and a dispersion that is essentially indefinitely stable to sedimentation.Petroleum Research Fund (ACS-PRF Grant No. 49956-ND9)American Chemical Society (ACS-PRF Grant No. 49956-ND9

Apocalyptic public health: exploring discourses of fatness in childhood ‘obesity’ policy

Recent‘ obesity’ preventions focus heavily on children, widely regarded as the future of society. The National Child Measurement Programme (NCMP) is a flagship government programme in England that annually measures the Body Mass Index (BMI) of children in Reception (aged 4–5) and Year 6 (aged 10 –11) in order to identify ‘at risk’ children and offer advice to parents. Using Foucauldian discourse analysis this study explore show discourses within the programme construct fatness. The NCMP materials contain three key interrelated themes (concerning the hidden threat of ‘obesity’, the burden of ‘obesity’, and bodies that pose a greater risk) that combine to construct a ‘grotesque discourse’ of apocalyptic public health. ‘Obesity’ is constructed as a social and economic catastrophe where certain bodies pose a greater threat than others. We argue that this discourse has the potential to change health service policy in markedly regressive ways that will disproportionately impact working-class, Black, Asian, and mixed race families

Understanding polyethylene surface functionalization by an atmospheric <tex>He/O_{2}$</tex> plasma through combined experiments and simulations

International audienceHigh density polyethylene surfaces were exposed to the atmospheric post-discharge of a radiofrequency plasma torch supplied in helium and oxygen. Dynamic water contact angle measurements were performed to evaluate changes in surface hydrophilicity and angle resolved x-ray photoelectron spectroscopy was carried out to identify the functional groups responsible for wettability changes and to study their subsurface depth profiles, up to 9 nm in depth. The reactions leading to the formation of C–O, C=O and O–C=O groups were simulated by molecular dynamics. These simulations demonstrate that impinging oxygen atoms do not react immediately upon impact but rather remain at or close to the surface before eventually reacting. The simulations also explain the release of gaseous species in the ambient environment as well as the ejection of low molecular weight oxidized materials from the surface

Preparation and characterization of thin organosilicon films deposited on SPR chip

International audienceThe paper reports on the preparation and characterization of organosilicon thin polymer films deposited on glass slides coated with 5 nm adhesion layer of titanium and 50 nm of gold. The polymer was obtained by the decomposition of 1,1,3,3-tetramethyldisiloxane precursor (TMDSO) premixed with oxygen induced in a N2 plasma afterglow using remote plasma-enhanced chemical vapor deposition (PECVD) technique. The film thickness was controlled by laser interferometry and was 9 nm. The chemical stability of the gold substrate coated with the organosilicon polymer film (p-TMDSO) was studied in different acidic and basic solutions (pH 1–14). While the gold/polymer interface showed a high stability in acidic media, the film was almost completely removed in basic solutions. The resulting surfaces were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), water contact angle measurements, cyclic voltammetry, and surface plasmon resonance (SPR)