The dynamics of fluid flow at the interface between elastic solids with rough surfaces depends sensitively on the area of real contact, in particular close to the percolation threshold, where an irregular network of narrow flow channels prevails. In this paper, numerical simulation and experimental results for the contact between elastic solids with isotropic and anisotropic surface roughness are compared with the predictions of a theory based on the Persson contact mechanics theory and the Bruggeman effective medium theory. The theory predictions are in good agreement with the experimental and numerical simulation results and the (small) deviation can be understood as a finite-size effect. The fluid squeeze-out at the interface between elastic solids with randomly rough surfaces is studied. We present results for such high contact pressures that the area of real contact percolates, giving rise to sealed-off domains with pressurized fluid at the interface. The theoretical predictions are compared to experimental data for a simple model system (a rubber block squeezed against a flat glass plate), and for prefilled syringes, where the rubber plunger stopper is lubricated by a high-viscosity silicon oil to ensure functionality of the delivery device. For the latter system we compare the breakloose (or static) friction, as a function of the time of stationary contact, to the theory prediction.

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A central paradigm that underpins our understanding of the interaction of proteins with solid surfaces is that protein adsorption leads to changes in secondary structure. The bound proteins tend to denature, and these non-native, adsorbed structures are likely stabilized through the loss of α-helices with the concomitant formation of intermolecular β-sheets. The goal of this work is to critically assess the impact this behavior has on protein desorption, where irreversible conformational changes might lead to protein aggregation or result in other forms of instability. The adsorption, desorption, and structural transitions of lysozyme are examined on fumed silica nanoparticles as a function of the amount of protein adsorbed. Surprisingly, the data indicate not only that adsorption is reversible but also that protein desorption is predictable in a coverage-dependent manner. Additionally, there is evidence of a two-state model which involves exchange between a native-like dissolved state and a highly perturbed adsorbed state. Since the in situ circular dichroism (CD) derived secondary structures of the adsorbed proteins are essentially unaffected by changes in surface coverage, these results are not consistent with previous claims that surface-induced denaturation is coverage dependent. Inspired by results from homopolymer adsorption experiments, we speculate that more local descriptors, such as the number of amino acids per chain that are physically adsorbed on the surface, likely control the desorption process.

A model for Si, SiCH, Si O 2 , SiOCH, and porous SiOCH etch rate calculation in inductively coupled fluorocarbon plasma with a pulsed bias: Importance of the fluorocarbon layer This study is dedicated to an analysis of the etch mechanisms of SiOCH, SiO 2 and SiCH in fluorocarbon plasmas. The etching of these materials is performed on blanket wafers in a magnetically enhanced reactive ion etcher reactor using fluorocarbon based chemistry (CF 4 /N 2 /Ar). After partial etching, the Fourier transform infrared spectroscopy and mercury probe measurement indicate that the remaining substrate of SiOCH is not altered by the reactive plasma. A decrease in the etch rate of SiOCH, SiO 2 and SiCH is observed either with increasing Ar dilution or polymerizing gas addition as CH 2 F 2 and C 4 F 6 . X-ray photoelectron spectroscopy analysis of the surface after partial etching shows that the thickness of the fluorocarbon layer formed at the film surface and its composition play a key role in controlling etch rate and selectivity of SiOCH, SiO 2 and SiCH. The etch rate of these materials is getting lower when the fluorocarbon layer thickness increases and also when its fluorine concentration decreases. The fluorocarbon layer thickness and composition depend on the plasma chemistry but also on the concentration and nature of impurities ͑C and H͒ in the etched materials. Etch rates are presented and discussed with respect to plasma parameters and material composition in terms of etching mechanisms.

We present experimental data for the static or breakloose friction for lubricated elastomer contacts, as a function of the time of stationary contact. Due to fluid squeeze-out from the asperity contact regions, the breakloose friction force increases continuously with the time of stationary contact. We consider three different cases: (a) PDMS rubber balls against flat smooth glass surfaces, (b) PDMS cylinder ribs against different substrates (glass, smooth and rough PMMA and an inert polymer) and (c) application to syringes. Due to differences in the surface roughness and contact pressures the three systems exhibit very different time dependences of the breakloose friction. In case (a) for rough surfaces the dry contact area A is a small fraction of the nominal contact area A0, and the fluid squeeze-out is fast. In case (b) the dry contact area is close to the nominal contact area, A/A0 ≈ 1, and fluid squeeze-out is very slow due to percolation of the contact area. In this case, remarkably, different fluids with very different viscosities, ranging from 0.005 Pa s (water–glycerol mixture) to 1.48 Pa s (glycerol), give very similar breakloose friction forces as a function of the time of stationary contact. In case (c) the contact pressure and the surface roughness are larger than in case (b), and the squeeze-out is very slow so that even after a very long time the area of real contact is below the percolation threshold. For all cases (a)–(c), the increase in the breakloose friction is mainly due to the increase in the area of real contact with increasing time, because of the fluid squeeze-out and dewetting.