The Atomic Force Microscope tip was used to progressively abrade the surface of non-cutted starch granules embedded in the endosperm protein matrix in grain sections from wheat near-isogenic lines differing in the puroindoline b gene and thus hardness. In the hard near-isogenic wheat lines, starch granules exhibited two distinct profiles corresponding either to abrasion in the surrounding protein layer or the starch granule. An additional profile, only identified in soft lines, revealed a marked stop in the abrasion at the protein-starch transition similar to a lipid interface playing a lubricant role. It was related to the presence of both wild-type puroindolines, already suggested to act at the starch-protein interface through their association with polar lipids.This study revealed, for the first time, in situ differences in the nano-mechanical properties at the starch-protein interface in the endosperm of wheat grains depending on the puroindoline allelic status.

Directed and true self-assembly mechanisms in nematic liquid crystal colloids rely on specific interactions between microparticles and the topological defects of the matrix. Most ordered structures formed in thin nematic cells are thus based on elastic multipoles consisting of a particle and nearby defects. Here, we report, for the first time to our knowledge, the existence of giant elastic dipoles arising from particles dispersed in free nematic liquid crystal films. We discuss the role of capillarity and film thickness on the dimensions of the dipoles and explain their main features with a simple 2D model. Coupling of capillarity with nematic elasticity could offer ways to tune finely the spatial organization of complex colloidal systems.

We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft–hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star–polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid–polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft–hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures.

An holographic microscopy reconstruction method compatible with high numerical aperture microscope objective (MO) up to NA=1.4 is proposed. After off axis and reference field curvature corrections, and after selection of the +1 grating order holographic image, a phase mask that transforms the optical elements of the holographic setup into an afocal device is applied in the camera plane. The reconstruction is then made by the angular spectrum method. The field is first propagated in the image half space from the camera to the afocal image of the MO optimal plane (plane for which MO has been designed) by using a quadratic kernel. The field is then propagated from the MO optimal plane to the object with the exact kernel. Calibration of the reconstruction is made by imaging a calibrated object like an USAF resolution target for different positions along z. Once the calibration is done, the reconstruction can be made with an object located in any plane z. The reconstruction method has been validated experimentally with an USAF target imaged with a NA=1.4 microscope objective. Near-optimal resolution is obtained over an extended range (±50 µm) of z locations.

Heterodyne holography is a variant of phase shifting holography in which reference and signal arms are controlled by acousto optic modulators. In this review paper, we will briefy describe the method and its properties, and we will illustrate its advantages in experimental applications.

We study the destabilization mechanism of thin liquid sheets expanding in air and show that dilute oil-in-water emulsion-based sheets disintegrate through the nucleation and growth of holes that perforate the sheet. The velocity and thickness fields of the sheet outside the holes are not perturbed by holes and hole opening follows a Taylor-Culick law. We find that a pre-hole, which widens and thins out the sheet with time, systematically precedes the hole nucleation. The growth dynamics of the pre-hole follows the law theoretically predicted for a liquid spreading on another liquid of higher surface tension due to Marangoni stresses. Classical Marangoni spreading experiments quantitatively corroborate our findings.

The clogging of porous media by colloidal particles is a complex process which relies on many different physical phenomena. The formation and the structure of a clog results from the interplay between hydrodynamics (flow rate and pore geometry) and the DLVO forces (particle–particle and particle–wall). In order to get a better understanding of this process, we study the clogging of a microfluidic filter, at the single pore level, and determine the influence of each relevant parameter separately. We show that in order to form stable clogs, colloidal particles have to pile up over a length in the flow direction roughly equal to the width of the pore. We found that there are two clogging regimes, which depend on the applied pressure. In the first one, at low pressures, the length of the clog within the pore and the number of particles that pass through the pore prior to clogging are constant. In the second one, for higher pressures, both quantities increase with the pressure. We also show that a higher ionic strength accelerates the clog formation, keeping constant the length of the clog