In some cases water droplets can completely wet microstructured superhydrophobic surfaces. The dynamics of this rapid process is analyzed by ultrahigh-speed imaging. Depending on the scales of the microstructure, the wetting fronts propagate smoothly and circularly or-more interestingly -in a stepwise manner, leading to a growing square-shaped wetted area: entering a new row perpendicular to the direction of front propagation takes milliseconds, whereas once this has happened, the row itself fills in microseconds (''zipping''). Numerical simulations confirm this view and are in quantitative agreement with the experiments.

We employ micro-particle image velocimetry (µ-PIV) to investigate laminar micro-flows in hydrophobic microstructured channels, in particular the slip length. These microchannels consist of longitudinal micro-grooves, which can trap air and prompt a shear-free boundary condition and thus slippage enhancement. Our measurements reveal an increase of the slip length when the width of the micro-grooves is enlarged. The result of the slip length is smaller than the analytical prediction by Philip et al. [1] for an infinitely large and textured channel comprised of alternating shear-free and no-slip boundary conditions. The smaller slip length (as compared to the prediction) can be attributed to the confinement of the microchannel and the bending of the meniscus (liquid-gas interface). Our experimental studies suggest that the curvature of the meniscus plays an important role in microflows over hydrophobic micro-ridges.

We experimentally study the dynamics of water in the Cassie-Baxter state to Wenzel state transition on surfaces decorated with assemblies of micrometer-size square pillars arranged on a square lattice. The transition on the micro-patterned superhydrophobic polymer surfaces is followed with a high-speed camera. Detailed analysis of the movement of the liquid during this transition reveals the wetting front velocity dependence on the geometry and material properties. We show that a decrease in gap size as well as an increase in pillar height and intrinsic material hydrophobicity result in a lower front velocity. Scaling arguments based on balancing surface forces and viscous dissipation allow us to derive a relation with which we can rescale all experimentally measured front velocities, obtained for various pattern geometries and materials, on one single curve.

The incorporation characteristics of three simple tetraarylporphyrins into bilayers of dioctadecyldimethylam monium surfactants was studied by UV-vis, fluorescence, and EPR spectroscopy. The porphyrins used are tetraphenylporphyrin (TPP), tetrakis(4-(hexadecyloxy)phenyl)porphyrin (THPP), and tris(4-(hexadecyloxy)-phenyl)(4-methylpyridinium)porphyrin tosylate (TrHPyP). At low porphyrin to surfactant molar ratios (<5 x 10"4) the porphyrins show a strong fluorescence. Increasing this ratio to 5 X 10~3 causes a change in the UV-vis spectra and a decrease of the fluorescence intensity. Time-resolved fluorescence measurements indicated that the latter is due to the formation of non-fluorescent porphyrin aggregates. The spectral characteristics of the porphyrin aggregates are discussed in terms of the formation of different types of aggregates. The location of the porphyrins within the bilayers was investigated by fluorescence quenching experiments using iodide, 9( 10)-bromooctadecanoic acid, and 16-bromohexadecanoic acid. These experiments suggest that THPP is located in the middle of the bilayer and TrHPyP near the aqueous interface. For the parent compound TPP no well-defined position was found. EPR spectroscopy on cast films of dioctadecyldimethylammonium surfactants with the copper derivatives of the porphyrins incorporated (porphyrin-to-surfactant ratio = 5 x 10~3) revealed a clear anisotropic distribution of the latter molecules in the cast bilayers. The angles between the porphyrin normals and the bilayer normal were determined by comparison of experiment with simulated spectra. In the case of THPP and TrHPyP these angles agree very well with an arrangement in which the long porphyrin axis lies parallel to the bilayer surface. The arrangement of TPP aggregates could not be established.

Drops deposited on rough and hydrophobic surfaces can stay suspended with gas pockets underneath the liquid, then showing very low hydrodynamic resistance. When this superhydrophobic state breaks down, the subsequent wetting process can show different dynamical properties. A suitable choice of the geometry can make the wetting front propagate in a stepwise manner leading to square-shaped wetted area: the front propagation is slow and the patterned surface fills by rows through a zipping mechanism. The multiple time scale scenario of this wetting process is experimentally characterized and compared to numerical simulations.

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A total of 351 women who gave birth in the Paddington and North Kensington Health District were studied in order to establish a factual basis for recording height and shoe size as indicators of pelvic adequacy. Because only 19 women had radiological pelvimetry assessment, type of delivery and length of labour were used as proxy measures of disproportion. Of the 57 women with a shoe size <4;, 21% were delivered by caesarean section compared with 10% of the group with shoe size between 4; and 6 and only 1% of the group with shoe size 36;. Similar relations with height were not generally found. The data were further examined using logistic regression models of the expected percentages of mothers having an adverse delivery. The models confirmed and extended the more simple analysis.

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