This paper reports some experimental results on two-phase flows in model two-dimensional porous media. Standard microfluidic techniques are used to fabricate networks of straight microchannels and control the throat size distribution. We analyze both invasion mechanism medium by a nonwetting fluid drainage after percolation for capillary numbers lying between 10(-7) 10(-2). propose crude allowing description observed fingering that captures its scaling properties. is supported numerical...

The dewetting of thin polystyrene films (20--500 nm) on a liquid substrate is studied at time scales that are long compared to the reptation time. It shown kinetics correspond those purely viscous flow and viscosity measured by this technique is, for thickest films, consistent with bulk measurements. Films order coil size then studied. effective these displays large decrease when film thickness $h$ below several radius gyration, ${R}_{g}$. This reduction found depend only ratio $h/{R}_{g}$.

Pattern formation from a silica colloidal suspension that is evaporating has been studied when movement imposed to the contact line. This article focuses on stick-slip regime observed for very low line velocities. A capillary rise experiment specially designed observation and allows us measure pinning force increases during of growing deposit. We report systematic measurements this derive scaling laws velocity line, colloid concentration, evaporation rate are varied. Our analysis supports...

We investigated the rheological properties of suspensions attractive microcapsules, which formed a weak gel at volume fractions ϕ as low 0.1. These measuring 100 μm in diameter, were constructed with droplet positively charged chitosan solution protected by membrane through complexation negatively surfactant. Iso-density matched achieved dispersing these microcapsules silicone oils. Plate-plate rheometry revealed that displayed yield stress ranging from about 0.1 to 3 Pa for increasing 0.5....

The dewetting of ultrathin polystyrene films on a liquid substrate is studied in the vicinity glass transition. This technique leads to measurement extensional creep compliance film. results reported this article show that rubbery plateau value unchanged for as thin 20 nm. Thus, we conclude entanglement density unaffected by surface at scale coil size. These are discussed context previous report reduction viscosity same films. Furthermore, segmental relaxation regime exhibits small...

This paper presents some experimental results on two-phase flows in model two-dimensional (2D) porous media with different wetting properties. Standard microfluidic techniques are used to fabricate the 2D micromodels that consist of a network straight microchannels having heterogeneous sizes. The invasion mechanism is analyzed quantitatively for partial and total conditions, various stable viscosity ratios capillary pressure heterogeneity. For numbers ranging from ${10}^{\ensuremath{-}7}$...

We present an experimental investigation of the drying kinetics seen from inside a sessile droplet laden with colloidal sol silica nanoparticles. use fast, two-color confocal microscopy imaging to quantitatively extract on one hand concentration field rhodamine-tagged nanosol and other velocity mobility large, fluorescein-tagged tracers. By changing initial at which drop dries up, we propose method that yields self-consistent way obtain rheology sol. Based these results, analyse in terms (i)...

We explore the flow of highly shear thinning polymer solutions in straight geometry. The strong variations normal forces close to wall give rise an elastic instability. evidence a periodic motion onset instability, which then evolves towards turbulentlike at higher rates. Strikingly, we point out that this instability induces genuine drag reduction due homogenization viscosity profile by turbulent flow.

Drying experiments with a receding contact line have been performed silica colloidal suspensions and polyacrylamide (PAAm) polymer solutions. The experimental setup allows to control the movement of evaporation flux separately. Deposit thickness as function these two parameters has investigated. different systems exhibit similar behavior: in regime very low capillary numbers deposit scaled by solute volume concentration rate is proportional inverse velocity. Both scaling exponent constant...

This work reports on an experimental study of elastic turbulence in a semi-dilute wormlike micelle system made highly betaine surfactant solution. The temporal evolution both rheological quantities and local flow properties is monitored by combining global rheology, optical visualization, ultrasonic velocimetry. Even at the smallest applied shear rates or stresses, we find that micellar sample develops large Weissenberg (Wi) numbers, leading to undergo transition turbulence....

Pressure-driven flows of high molecular weight polyacrylamide solutions are examined in nanoslits using fluorescence photobleaching. The effective viscosity polymer decreases when the channel height below micron scale. In addition, apparent slippage is characterized macroscopically on similar surfaces. Though can explain qualitatively reduction, a quantitative comparison shows that slip length greatly reduced This result indicates chain migration suppressed confined geometries.

A numerical study of sheared suspensions frictional and frictionless rigid spheres finds that macroscopic friction in granular is nearly independent interparticle contact friction, besides lubrication, the viscous contribution pore fluid negligibly small.

We study flows of hydrolized polyacrylamide solutions in two dimensional porous media made using microfluidics, for which elastic effects are dominant. focus on semi-dilute (0.1%-0.4%) exhibit a strong shear thinning behavior. systematically measure the pressure drop and find that effective permeability is dramatically higher than predicted when Weissenberg number greater about 10. Observations streamlines flow reveal this effect coincides with onset instabilities. Moreover, importantly...

Abstract The rheology of sputum is viewed as a powerful emerging biophysical marker for monitoring muco-obstructive pulmonary diseases such cystic fibrosis (CF) and non-CF bronchiectasis (NCFB). However, there no unified practice to process sputa from collection analysis, which can lead highly variable, sometimes inconsistent results. main objective this study bring light into the handling samples establish standardised robust protocol before rheological measurements. Sputum collected 22 CF...

Tapping mode atomic force microscopy is frequently used to image the surface of soft materials; it also a powerful technique for nanomechanical analysis surfaces. We report here an investigation depth sensing method on polymers. The chosen approach based phase images model filled elastomer material. It leads determination depths hard particles lying under surface. found that tapping can probe interfaces buried up 80 nm polymer. Under given conditions, penetration tip into polymer observed...

Velocity measurement is a key issue when studying flows below the micron scale, due to lack of sensitivity conventional detection techniques. We present an approach based on fluorescence photobleaching evaluate flow velocity at nanoscale by direct visualization. Solutions containing fluorescent dye are injected into nanoslits. A photobleached line, created through laser beam illumination, moves channel fluid flow. The and effective diffusion coefficient calculated from temporal data line...

We use X-ray imaging to study viscous resuspension. In a Taylor-Couette geometry, we shear an initially settled layer of spherical glass particles immersed in Newtonian fluid and measure the local volume fraction profiles. this configuration, steady-state profiles are simply related normal viscosity defined framework suspension balance model. These experiments allow us examine fundamental quantity over wide range fractions, particular, semidilute regime where experimental data sorely...