1,745 research outputs found
Drainage of a nanoconfined simple fluid: rate effects on squeeze-out dynamics
We investigate the effect of loading rate on drainage in molecularly thin
films of a simple fluid made of quasi-spherical molecules
(octamethylcyclotetrasiloxane, OMCTS). We find that (i) rapidly confined OMCTS
retains its tendency to organize into layers parallel to the confining
surfaces, and (ii) flow resistance in such layered films can be described by
bulklike viscous forces if one accounts for the existence of one monolayer
immobilized on each surfaces. The latter result is fully consistent with the
recent work of Becker and Mugele, who reached a similar conclusion by analyzing
the dynamics of squeeze-out fronts in OMCTS [T. Becker and F. Mugele, Phys.
Rev. Lett. {\bf 91} 166104(2003)]. Furthermore, we show that the confinement
rate controls the nature of the thinning transitions: layer-by-layer expulsion
of molecules in metastable, slowly confined films proceeds by a
nucleation/growth mechanism, whereas deeply and rapidly quenched films are
unstable and undergo thinning transitions akin to spinodal decomposition
Dynamic surface decoupling in a sheared polymer melt
We propose that several mechanisms contribute to friction in a polymer melt
adsorbed at a structured surface. The first one is the well known
disentanglement of bulk polymer chains from the surface layer. However, if the
surface is ideal at the atomic scale, the adsorbed parts of polymer chains can
move along the equipotential lines of the surface potential. This gives rise to
a strong slippage of the melt. For high shear rates chains partially desorb.
However, the friction force on adsorbed chains increases, resulting in
quasi-stick boundary conditions. We propose that the adsorbed layers can be
efficiently used to adjust the friction force between the polymer melt and the
surface
Low Friction Flows of Liquids at Nanopatterned Interfaces
With the recent important development of microfluidic systems,
miniaturization of flow devices has become a real challenge. Microchannels,
however, are characterized by a large surface to volume ratio, so that surface
properties strongly affect flow resistance in submicrometric devices. We
present here results showing that the concerted effect of wetting . properties
and surface roughness may considerably reduce friction of the fluid past the
boundaries. The slippage of the fluid at the channel boundaries is shown to be
drastically increased by using surfaces that are patterned at the nanometer
scale. This effect occurs in the regime where the surface pattern is partially
dewetted, in the spirit of the 'superhydrophobic' effects that have been
recently discovered at the macroscopic scales. Our results show for the first
time that, in contrast to the common belief, surface friction may be reduced by
surface roughness. They also open the possibility of a controlled realization
of the 'nanobubbles' that have long been suspected to play a role in
interfacial slippag
Equilibrium Simulation of the Slip Coefficient in Nanoscale Pores
Accurate prediction of interfacial slip in nanoscale channels is required by
many microfluidic applications. Existing hydrodynamic solutions based on
Maxwellian boundary conditions include an empirical parameter that depends on
material properties and pore dimensions. This paper presents a derivation of a
new expression for the slip coefficient that is not based on the assumptions
concerning the details of solid-fluid collisions and whose parameters are
obtainable from \textit{equilibrium} simulation. The results for the slip
coefficient and flow rates are in good agreement with non-equilibrium molecular
dynamics simulation.Comment: 11 pages, 4 figures, submitted to Phys Rev Let
Boundary induced non linearities at small Reynolds Numbers
We investigate the influence of boundary slip velocity in Newtonian fluids at
finite Reynolds numbers. Numerical simulations with Lattice Boltzmann method
(LBM) and Finite Differences method (FDM) are performed to quantify the effect
of heterogeneous boundary conditions on the integral and local properties of
the flow. Non linear effects are induced by the non homogeneity of the boundary
condition and change the symmetry properties of the flow inducing an overall
mean flow reduction. To explain the observed drag modification, reciprocal
relations for stationary ensembles are used, predicting a reduction of the mean
flow rate from the creeping flow to be proportional to the fourth power of the
friction Reynolds number. Both numerical schemes are then validated within the
theoretical predictions and reveal a pronounced numerical efficiency of the LBM
with respect to FDM.Comment: 29 pages, 10 figure
Diffusion in pores and its dependence on boundary conditions
We study the influence of the boundary conditions at the solid liquid
interface on diffusion in a confined fluid. Using an hydrodynamic approach, we
compute numerical estimates for the diffusion of a particle confined between
two planes. Partial slip is shown to significantly influence the diffusion
coefficient near a wall. Analytical expressions are derived in the low and high
confinement limits, and are in good agreement with numerical results. These
calculations indicate that diffusion of tagged particles could be used as a
sensitive probe of the solid-liquid boundary conditions.Comment: soumis \`a J.Phys. Cond. Matt. special issue on "Diffusion in
Liquids, Polymers, Biophysics and Chemical Dynamics
Nonequilibrium molecular dynamics simulation of rapid directional solidification
We present the results of non-equilibrium molecular dynamics simulations for
the growth of a solid binary alloy from its liquid phase. The regime of high
pulling velocities, , for which there is a progressive transition from
solute segregation to solute trapping, is considered. In the segregation
regime, we recover the exponential form of the concentration profile within the
liquid phase. Solute trapping is shown to settle in progressively as is
increased and our results are in good agreement with the theoretical
predictions of Aziz [J. Appl. Phys. {\bf 53}, 1158 (1981)]. In addition, the
fluid advection velocity is shown to remain directly proportional to , even
at the highest velocities considered here (ms).Comment: Submitted to Phys. Rev.
Nintedanib in patients with idiopathic pulmonary fibrosis: Combined evidence from the TOMORROW and INPULSISÂź trials
AbstractBackground and purposeThe Phase II TOMORROW trial and two Phase III INPULSISÂź trials investigated the efficacy and safety of nintedanib versus placebo in patients with idiopathic pulmonary fibrosis (IPF). To obtain an overall estimate of the treatment effect of nintedanib 150 mg twice daily (bid), pooled and meta-analyses of data from these three trials were conducted.MethodsPooled and meta-analyses were conducted for annual rate of decline in forced vital capacity (FVC), time to first acute exacerbation, change from baseline in St George's Respiratory Questionnaire (SGRQ) total score and mortality over 52 weeks.Results1231 patients (nintedanib n = 723, placebo n = 508) were included in the pooled analysis. Adjusted annual rate of decline in FVC was â112.4 mL/year with nintedanib and â223.3 mL/year with placebo (difference: 110.9 mL/year [95% CI: 78.5, 143.3]; p < 0.0001). The hazard ratio for time to first acute exacerbation was 0.53 (95% CI: 0.34, 0.83; p = 0.0047). Adjusted mean change from baseline in SGRQ score at week 52 was 2.92 with nintedanib and 4.97 with placebo (difference: â2.05 [95% CI: â3.59, â0.50]; p = 0.0095). Hazard ratios for time to all-cause and on-treatment mortality were 0.70 (95% CI: 0.46, 1.08; p = 0.0954) and 0.57 (95% CI: 0.34, 0.97; p = 0.0274), respectively, in favour of nintedanib. The meta-analysis was generally consistent with the pooled analysis. Diarrhoea was the most frequent adverse event in the nintedanib group (61.5% of patients treated with nintedanib versus 17.9% of patients treated with placebo).ConclusionNintedanib has a beneficial effect on slowing disease progression in patients with IPF
- âŠ