Capturing aerosol droplets with fibers.

Capturing droplets from a stream with a fibrous material is a well-known and well-used process, from coalescence filters to fog harvesting. In this paper, we report experimental measurements of collection efficiency with a model system consisting in an array of vertical nylon fibers. In particular, we report precise measurements over a large range of parameters, and identify the key role played by the drop distribution on the overall collection efficiency. Due to a growth and coalescence process, this drop distribution evolves toward a regular pattern of uniformly distributed drops, and a balance between capillarity and gravity sets an average drop size. Accounting for these effects in a simple inertial impaction model allows predictive and quantitative comparisons with experiments. Drop growth can be suppressed by forming long continuous liquid columns between close fibers; incoming droplets immediately coalesce with these wet columns, and the capture efficiency is increased. In addition, we extend our model to take into account the interactions between fibers.

Wetting of flexible fibre arrays.

Fibrous media are functional and versatile materials, as demonstrated by their ubiquity both in natural systems such as feathers and adhesive pads and in engineered systems from nanotextured surfaces to textile products, where they offer benefits in filtration, insulation, wetting and colouring. The elasticity and high aspect ratios of the fibres allow deformation under capillary forces, which cause mechanical damage, matting self-assembly or colour changes, with many industrial and ecological consequences. Attempts to understand these systems have mostly focused on the wetting of rigid fibres or on elastocapillary effects in planar geometries and on a fibre brush withdrawn from an infinite bath. Here we consider the frequently encountered case of a liquid drop deposited on a flexible fibre array and show that flexibility, fibre geometry and drop volume are the crucial parameters that are necessary to understand the various observations referred to above. We identify the conditions required for a drop to remain compact with minimal spreading or to cause a pair of elastic fibres to coalesce. We find that there is a critical volume of liquid, and, hence, a critical drop size, above which this coalescence does not occur. We also identify a drop size that maximizes liquid capture. For both wetting and deformation of the substrates, we present rules that are deduced from the geometric and material properties of the fibres and the volume of the drop. These ideas are applicable to a wide range of fibrous materials, as we illustrate with examples for feathers, beetle tarsi, sprays and microfabricated systems.

Liquid film coating a fiber as a model system for the formation of bound states in active dispersive-dissipative nonlinear media.

We analyze the coherent-structure interaction and the formation of bound states in active dispersive-dissipative nonlinear media using a viscous film coating a vertical fiber as a prototype. The coherent structures in this case are droplike pulses that dominate the evolution of the film. We study experimentally the interaction dynamics and show evidence for formation of bound states. A theoretical explanation is provided through a coherent-structures theory of a simple model for the flow.

Human immunodeficiency virus type 1 IgA antibody in breast milk and serum.

Breast-feeding plays a potentially significant role in mother to child transmission of human immunodeficiency virus type 1 (HIV-1). The additional transmission risk attributable to breast-feeding and the factors that enhance or inhibit transmission are presently unknown. One mechanism by which breast milk might inhibit HIV-1 transmission is the presence of specific antibodies directed against HIV-1 in breast milk of seropositive mothers. In this study serum and breast milk samples from women in Nairobi, Kenya, were tested to determine the prevalence of HIV-1 IgA antibodies. A Western blot test developed in our laboratory was used to detect anti-HIV-1 immunoglobulin A in serum and anti-HIV-1 secretory IgA (sIgA) in breast milk. Ninety-four percent of 63 HIV-1 seropositive women had anti-HIV-1 IgA in serum and 59% had anti-HIV-1 sIgA in their breast milk. No significant associations with maternal characteristics or serum anti-HIV-1 IgA or IgG banding patterns and the presence of anti-HIV-1 sIgA in breast milk were found. No protective effect of anti-HIV-1 sIgA was seen regarding mother to child transmission; however, further studies are necessary to determine the effect of these antibodies in maternal sera or in breast milk on the efficacy of HIV-1 transmission.

Absolute and convective instabilities of a viscous film flowing down a vertical fiber.

The stability of a viscous film flowing down a vertical fiber under the action of gravity is analyzed both experimentally and theoretically. At large or small film thicknesses, the instability is convective, whereas an absolute instability mode is observed in an intermediate range of film thicknesses for fibers of small enough radius. The onset of the experimental irregular wavy regime corresponds precisely to the theoretical prediction of the threshold of the convective instability.

[Synthesis of functionalized cyanines. Fluorescence properties following complexation of cations]. / Synthèse de cyanines fonctionnalisées. Etude de leurs propriétés de fluorescence en fonction de la complexation de cations.

The ionophoric properties of podands containing dioxazaphosphocane moieties linked by inactive spacers were studied. To increase the detection sensibility of these compounds we introduced a cyanine as spacer. Fluorescence analysis demonstrated the interest of cyanines as active spacers since the complexation by cations as Ca2+ and Mg2+ gives an enhancement of the emission intensity.