A large body of experimental work on the microstructure and dynamics of simplifiedindustrial nanocomposites made of disordered silica filler in a styrene-butadiene matrixby solid-phase mixing is regrouped and critically discussed in this feature article. Recentresults encompass systems with varying polymer mass, grafting functionality, and fillercontent. They have been obtained by simulation-based structural modelling of nanoparticleaggregate size and mass deduced from small-angle scattering and transmission electronmicroscopy. Our model has been validated by independent swelling experiments.Comparison of structurally-close nanocomposites of widely different chain mass led tothe identification of a unique structure-determining parameter, the grafting density, aswell as to a unified picture of aggregate formation mechanisms in complex nanocompositesduring mixing. In addition, low-field proton NMR allowed for the characterization ofdynamically slowed-down (‘glassy’) polymer layers, which were shown not to dominatethe rheological response, unlike the structural contribution. Finally, broadband dielectricspectroscopy was used in an innovative manner to identify filler percolation – also identifiedby rheology – via dynamics along filler surfaces.

To investigate the interplay between microscopic dynamics and macroscopic rheology insoft matter, we couple a stress-controlled-rheometer equipped with a Couette cell to a lightscattering setup in the imaging geometry, which allows us to measure both the deformationfield and the microscopic dynamics. To validate our setup, we test two model systems. For anelastic solid sample, we recover the expected deformation field within 1 μm. For a pure viscousfluid seeded with tracer particles, we measure the velocity profile and the dynamics of thetracers, both during shear and at rest. The velocity profile is acquired over a gap of 5 mm witha temporal and spatial resolution of 1 s and 100 μm, respectively. At rest, the tracer dynamicshave the expected diffusive behavior. Under shear, the microscopic dynamics corrected for theaverage drift due to solid rotation scale with the local shear rate, demonstrating that our setupcaptures correctly the relative motion of the tracers due to the affine deformation.

Janus colloidal particles show remarkable properties in terms of surface activity, self-assembly and wetting. Moreover they can perform autonomous motion if they can chemically react with the liquid in which they are immersed. In order to understand the self-propelled motion of catalytic Janus colloids at the air-water interface, wetting and the orientation of the catalytic surface are important properties to be investigated. Wetting plays a central role in active motion since it determines the contact between fuel and catalytic surface as well as the efficiency of transduction of chemical reaction into motion. Active motion is not expected to occur either when the catalytic face is completely out of the aqueous phase or when the Janus boundaries are parallel to the interfacial plane. The design of a Janus colloid possessing two hydrophilic faces is required to allow the catalytic face to react with the fuel (e.g. H2O2 for Platinum) in water and to permit some rotational freedom of the Janus colloid in order to generate propulsion parallel to the interfacial plane.Here, we discuss some theoretical aspects that should be accounted when studying Janus colloids at the surface of water. The free energy of ideal Janus colloidal particles at the interface is modeled as a function of the immersion depth and the particle orientation. Analytical expressions of the energy profiles are established. Energetic aspects are then discussed in relation to the particle ability to rotate at the interface. By introducing contact angle hysteresis we describe how the effects of contact line pinning modifies the scenario described in the ideal case. Experimental observations of the contact angle hysteresis of Janus colloids at the interface reveal the effect of pinning; and orientations of silica particles half covered with a platinum layer at the interface do not comply with the ideal scenarios. Experimental observations suggest that Janus colloids at the fluid interface behave as kinetically driven system, where the contact line motion over defects decorating the Janus faces rules the orientation and rotational diffusion of the particle.

The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces. MHz frequency ultrasound was applied normal to the interface at relatively low ultrasonic pressures (< 0.6 MPa), and the amplitudes of surface fluctuations have been measured by light reflectivity and ellipsometry. We found a dramatic enhancement of surface roughness, roughly linear with intensity, with vertical displacements of the interface as high as 50-100 nm. As a consequence, the effective contact area between two fluids can be increased by ultrasound. This result has a clear impact for enhancing interface based processes such as mass or heat transfer.

Microvessel blood flow imaging techniques are widely used in biomedical research and clinical diagnostics where many diseases have a vascular etiology or involvement. For testing purposes, zebrafish embryo provides an ideal animal model to achieve high-resolution imaging of superficial and deeply localized vessels. Moreover, the study of the formation of a closed circulatory system in vertebrates is a topic of recent interest in biophysics. However, most of the existing techniques are invasive due to the use of a contrast agent for imaging purposes. Recent developments in Digital Holography and Laser Doppler Holography techniques can be considered to alleviate this issue. Laser Doppler holography and transmission microscopy can be coupled to analyze blood flow in fish embryos by adapting a laser Doppler holographic setup to a standard bio-microscope: the two beams of the holographic interferometer (illumination of the object and reference), whose frequency offset is controlled, were addressed to the microscope by optical fibers. Multimodal acquisition and analysis of the data is made by acting on the frequency offset of the two beams, and on the location of the Fourier space filtered zone. In this work, we show that it is possible to select the signal of moving scatterers, and to image Red Blood Cells (RBCs) and blood vessels. Individual RBCs are imaged, and movies showing the RBC motion are obtained. Microsc. Res. Tech., 2016. © 2016 Wiley Periodicals, Inc.

We investigate the nucleation and propagation of cracks in self-assembled viscoelastic fluids, which are made of surfactant micellesreversibly linked by telechelic polymers. The morphology of the micelles can be continuously tuned, from spherical to rodlike towormlike, thus producing transient double networks when the micelles are sufficiently long and entangled and transient singlenetworks otherwise. For a single network, we show that cracks nucleate when the sample deformation rate involved is comparable tothe relaxation time scale of the network. For a double network, by contrast, significant rearrangements of the micelles occuras a crack nucleates and propagates. We show that birefringence develops at the crack tip over a finite length, ξ, whichcorresponds to the length scale over which micelle alignment occurs. We find that ξ is larger for slower cracks, suggesting anincrease of ductility.

An original technique that combines digital holography, dual illumination of the sample and cleaning algorithm 3D reconstruction is proposed. It uses a standard transmission microscopy setup coupled with a digital holography detection. The technique is 4D, since it allows to determine, at each time step, the 3D locations (x, y, z) of many moving objects that scatter the dual illumination beam. The technique has been validated by imaging the microcirculation of blood in a fish larvae sample (the moving objects are thus red blood cells RBCs). Videos showing in 4D the moving RBCs superimposed with the perfused blood vessels are obtained.