Metastability of a Periodic Network of Threads: Shapes of a Knitted Fabric.

Knitted fabrics are metamaterials with remarkable mechanical properties, such as extreme deformability and multiple history-dependent rest shapes. This Letter shows that those properties may stem from a continuous set of metastable states for a fabric free of external forces. This is evidenced through experiments, numerical simulations, and analytical developments.

Effect of Surface Chemistry on the Electrical Double Layer in a Long-Chain Ionic Liquid.

Room temperature ionic liquids (ILs) can create a strong accumulation of charges at solid interfaces by forming a very thin and dense electrical double layer (EDL). The structure of this EDL has important consequences in numerous applications involving ILs, for example, in supercapacitors, sensors, and lubricants, by impacting the interfacial capacitance, the charge carrier density of semiconductors, as well as the frictional properties of the interfaces. We have studied the interfacial structure of a long chain imidazolium-based IL (1-octyl-3-methylimidazolium dicyanamide) on several substrates: mica, silica, silicon, and molybdenum disulfide (MoS), using atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulations.

Apparent Non-Newtonian Behavior of Ionic Liquids.

A significant viscosity variation with the shear rate has been observed for several ionic liquids in rheometry experiments above a critical shear rate. Depending on the liquid and the rheological conditions, both viscosity increase and decrease have been reported. So far, these variations have been interpreted as a signature of a non-Newtonian behavior.

Capillary force on a tilted cylinder: Atomic Force Microscope (AFM) measurements.

Hypothesis: The capillary force in situations where the liquid meniscus is asymmetric, such as the one around a tilted object, has been hitherto barely investigated even though these situations are very common in practice. In particular, the capillary force exerted on a tilted object may depend on the dipping angle i.

Experiments: We investigate experimentally the capillary force that applies on a tilted cylinder as a function of its dipping angle i, using a home-built tilting Atomic Force Microscope (AFM) with custom made probes.

Functionalized AFM probes for force spectroscopy: eigenmode shapes and stiffness calibration through thermal noise measurements.

The functionalization of an atomic force microscope (AFM) cantilever with a colloidal bead is a widely used technique when the geometry between the probe and the sample must be controlled, particularly in force spectroscopy. But some questions remain: how does a bead glued at the end of a cantilever influence its mechanical response? And more importantly for quantitative measurements, can we still determine the stiffness of the AFM probe with traditional techniques?In this paper, the influence of the colloidal mass loading on the eigenmode shape and resonant frequency is investigated by measuring the thermal noise on rectangular AFM microcantilevers with and without beads attached at their extremities. The experiments are performed with a home-made ultra-sensitive AFM, based on differential interferometry.

Why can artificial membranes be fabricated so rapidly in microfluidics?

Droplet interface bilayers are a convenient tool to produce and explore lipid membrane properties. We discuss why their formation time in microfluidics can be three to six orders of magnitude faster compared to conventional bulk settings.

Hydrodynamic interaction between a spherical particle and an elastic surface: a gentle probe for soft thin Films.

We study the hydrodynamic interaction between a sphere and an elastic surface at a nanoscale with a dynamic surface force apparatus. We show that the interplay between viscous forces and elastic deformations leads to very rich scaling properties of the force response, providing a unique signature of the surface elastic behavior. These properties are illustrated on three different examples: a thick elastomer, a thin elastomer film, and a layer of micrometric bubbles.

Nanohydrodynamics: the intrinsic flow boundary condition on smooth surfaces.

A dynamic surface force apparatus is used to determine the intrinsic flow boundary condition of two simple liquids, water and dodecane, on various smooth surfaces. We demonstrate the impact of experimental errors and data analysis on the accuracy of slip length determination. In all systems investigated, the dissipation is described by a well-defined boundary condition accounting for a whole range of separation, film thickness, and shear rate.

High friction on a bubble mattress.

Reducing the friction of liquid flows on solid surfaces has become an important issue with the development of microfluidics systems, and more generally for the manipulation of fluids at small scales. To achieve high slippage of liquids at walls, the use of gas as a lubricant--such as microbubbles trapped in superhydrophobic surfaces--has been suggested. The effect of microbubbles on the effective boundary condition has been investigated in a number of theoretical studies, which basically show that on flat composite interfaces the magnitude of the slippage is proportional to the periodicity of the gaseous patterns.