Nanoparticle Taylor Dispersion Near Charged Surfaces with an Open Boundary.

The dispersive spreading of microscopic particles in shear flows is influenced both by advection and thermal motion. At the nanoscale, interactions between such particles and their confining boundaries become unavoidable. We address the roles of electrostatic repulsion and absorption on the spatial distribution and dispersion of charged nanoparticles in near-surface shear flows, observed under evanescent illumination.

Near-surface rheology and hydrodynamic boundary condition of semi-dilute polymer solutions.

Understanding confined flows of complex fluids requires simultaneous access to the mechanical behaviour of the liquid and the boundary condition at the interfaces. Here, we use evanescent wave microscopy to investigate near-surface flows of semi-dilute, unentangled polyacrylamide solutions. By using both neutral and anionic polymers, we show that monomer charge plays a key role in confined polymer dynamics.

Asymptotic turbulent friction in 2D rough-walled flows.

The friction is the property of wall-bounded flows that sets the pumping cost of a pipeline, the draining capacity of a river, and other variables of practical relevance. For highly turbulent rough-walled pipe flows, depends solely on the roughness length scale , and the - relation may be expressed by the Strickler empirical scaling ∝ Here, we show experimentally that for soap film flows that are the two-dimensional (2D) equivalent of highly turbulent rough-walled pipe flows, ∝ and the - relation is not the same in 2D as in 3D. Our findings are beyond the purview of the standard theory of friction but consistent with a competing theory in which is linked to the turbulent spectrum via the spectral exponent α: In 3D, α = 5/3 and the theory yields ∝ ; in 2D, α = 3 and the theory yields ∝ .

Large variability in the motility of spiroplasmas in media of different viscosities.

Spiroplasmas are bacteria that do not possess flagella and their motility is linked to kink propagation coupled to changes in the cell body helicity. While the motility of bacteria with flagellar motion has been studied extensively, less work has been devoted to the motility of spiroplasmas. We first show that the motility of such bacteria has large variability from individual to individual as well as large fluctuations in time.

Detrimental impact of silica nanoparticles on the nanomechanical properties of Escherichia coli, studied by AFM.

Despite great innovative and technological promises, nanoparticles (NPs) can ultimately exert an antibacterial activity by affecting the cell envelope integrity. This envelope, by conferring the cell its rigidity and protection, is intimately related to the mechanical behavior of the bacterial surface. Depending on their size, surface chemistry, shape, NPs can induce damages to the cell morphology and structure among others, and are therefore expected to alter the overall mechanical properties of bacteria.

Structure of velocity distributions in shock waves in granular gases with extension to molecular gases.

Velocity distributions in normal shock waves obtained in dilute granular flows are studied. These distributions cannot be described by a simple functional shape and are believed to be bimodal. Our results show that these distributions are not strictly bimodal but a trimodal distribution is shown to be sufficient.

Stokes-Einstein diffusion of colloids in nematics.

We report the experimental observation of anisotropic diffusion of polystyrene particles immersed in a lyotropic liquid crystal with two different anchoring conditions. Diffusion is shown to obey the Stokes-Einstein law for particle diameters ranging from 190 nm up to 2 μm. In the case of prolate micelles, the beads diffuse four times faster along the director than in perpendicular directions, D||/D[Symbol: see text] ≈ 4.