39 research outputs found
Differential Dynamic Microscopy to characterize Brownian motion and bacteria motility
We have developed a lab work module where we teach undergraduate students how
to quantify the dynamics of a suspension of microscopic particles, measuring
and analyzing the motion of those particles at the individual level or as a
group. Differential Dynamic Microscopy (DDM) is a relatively recent technique
that precisely does that and constitutes an alternative method to more
classical techniques such as dynamics light scattering (DLS) or video particle
tracking (VPT). DDM consists in imaging a particle dispersion with a standard
light microscope and a camera. The image analysis requires the students to code
and relies on digital Fourier transform to obtain the intermediate scattering
function, an autocorrelation function that characterizes the dynamics of the
dispersion. We first illustrate DDM on the textbook case of colloids where we
measure the diffusion coefficient. Then we show that DDM is a pertinent tool to
characterize biologic systems such as motile bacteria i.e.bacteria that can
self propel, where we not only determine the diffusion coefficient but also the
velocity and the fraction of motile bacteria. Finally, so that our paper can be
used as a tutorial to the DDM technique, we have joined to this article movies
of the colloidal and bacterial suspensions and the DDM algorithm in both Matlab
and Python to analyze the movies
Poly(ionic liquid)s with controlled architectures and their use in the making of ionogels with high conductivity and tunable rheological properties
International audienceWe describe the preparation as well as the electrochemical and mechanical properties of a series of novel well-defined poly(ionic liquids) (PILs) featuring a finely tuned cross-linking ratio. We generate a variety of such PILs with various cationic moieties and cross-linking ratios starting from a common polymeric platform. Mixing those polymers with an appropriate ionic-liquid leads to ionogel electrolytes exhibiting good ionic conductivities (up to 1.2 mS cm−1 at 298 K), high electrochemical stability (up to 6 V) and a yield-stress fluid mechanical behavior, which enables their use as solid electrolytes. We demonstrate that depending on the cationic moieties, this ability to be solid at rest and reversibly fluid when sheared is obtained by two different mechanisms