A holographic microscopy method using several illuminations beams with a NA=0.5 aperture objective is proposed to image blood microcirculation in zebrafish larvae. Recent achievements in 3D imaging of blood flow are presented.

A versatile and eco-compatible preparation route of functional ordered mesoporous materials will be described. It relies on the use of assemblies of hydrophilic diblock copolymers, in place of classical amphiphilic templates, as new structuring and functionalizing agents for the direct synthesis, at room temperature and in water, of polymer-functionalized mesoporous silica.The new structuring agents are dynamic PolyIon electrostatic Complex (PIC) micelles formed between double-hydrophilic-block-copolymers (DHBC) (constituted of a neutral block and an ionizable one) and an oppositely charged homopolyelectrolyte, which can be considered as an auxiliary of micellization of DHBC polymers.The different advantages of using PIC micelles are the following: due to their sensitivity to physicochemical parameters, PIC micelles allowed obtaining various hybrid mesostructures (cubic, 2D-hexagonal, lamellar...) by simply adjusting the material synthesis conditions using a unique DHBC/homopolyelectrolyte system. This is a consequence of the adjustable composition and water content of the polyion complex phase. The micellization process, which can be controlled by pH or ionic strength, is reversible in water and this allowed the recovery and recycling of the porogen polymers.Very interestingly, the use of PIC micelles permitted the direct preparation of polymer-functionalized mesopores. This was possible due to the easy dissociation of the polyion complex within the pores, selectively releasing the auxiliary of micellization while the DHBC remained for functionalizing the pores. This new method ensures an homogeneous functionalization of the mesopores, a control of the functional polymer chain lengths and a sufficient mesoporous volume. Moreover, the properties of the functional chains could be varied (acid, basic, metal-complexing...). Finally, this preparation route was extended to bio-functional hybrid mesophases useful as drug delivery systems [3] The direct formation of drug-loaded polymer-functionalized mesoporous materials was developed by using drug-polymer complex micelles as structuring agents ; this was shown with antibiotics exhibiting a pH-triggered release. Furthermore, studies are currently under way to estimate the catalytic performances of the new functional materials.

Double hydrophilic block copolymers (DHBC) in the presence of multivalent oppositely charged ions form polyion complexes (PIC) in the micellar form. We use PIC micelles as an ecofriendly structuring agents for templating ordered mesoporous materials [1,2] : after concomittant micellization and silica condensation, the porosity of the final material is revealed by simple elution in water and the polyions can be recycled in successive synthesis batches. Various mesoporous silica materials have been obtained from cubic to lamellar, although lyotropic behavior of PIC micelles on their own has seldom been reported if ever. Moreover, the control over the structure of the final material is not solely determined by the asymmetry ratio of the diblock copolymer : a single PIC system yields different mesostructured silica materials depending on the physico-chemical conditions. In an attempt to address the relation between the mesoporous material structure and the lyotropic behavior of these new templating agents, our attention was brought to the role of water which is actually a prominent constituent of PIC micelles.PIC micelles of PEO-b-PAA/oligoamines have been studied. The water content of the core of the micelles has been addressed by establishing the complete phase diagram of the polyelectrolyte complex PAA/oligoamine in its coacervate form. It amounts to 50%, varies non-monotonously with concentration and can be tuned by ionic strength, pH. Shape transition and phase transition are revealed by swelling laws of the correlation peak position obtained from X-ray scattering. From light scattering and osmometry we establish the equation of state  of a PEO-b-PAA/oligoamine electrostatic complex. Its lyotropic behavior is characterized by a transition of shape of the micelles at =0.16 and a transition to lamellar phase at =0.30 corresponding to various levels of deswelling of the corona and of the core.This study evidences the high compressibility of the core of the micelles as opposed to the core of amphiphilic copolymer micelles. This feature probably explains why lyotropic behavior of PIC micelles is less rich than the one of amphiphilic micelles. But it also brings versatility in the use of PIC micelles as templating agents for mesoporous materials.

Upon pH stimulus, double hydrophilic block copolymers form polyion complexes (PIC) in the micellar form. We used PIC micelles as ecofriendly templates for the synthesis of ordered mesoporous materials. The porosity of the final material is revealed by simple inversion of the pH stimulus. Various mesoporous silica materials have been obtained from cubic to lamellar.The control over the structure of the final material is expected to relate to the lyotropic behavior just as observed when micelles of amphiphilic molecules are used as template. However such lyotropic behavior has never been reported for PIC micelles. Moreover the same PIC leads to different structured silica materials depending on the physico-chemical conditions.Using X-rays and light scattering, optical microscopy and osmometry, we establish the equation of state (osmotic pressure vs volume fraction) of a PEO-b-PAA/oligoamine electrostatic complex. Its lyotropic behavior is characterized by a transition of shape at 0.16 w/w and a transition to a lamellar phase at 0.30w/w. The water content of the core of the micelles is addressed from the complete phase diagram of the polyelectrolyte complex in its coacervate form and explains why a single complex leads to porous material of different structure.

Une configuration de microscopie holographique qui utilise trois faisceaux d'illumination est proposée. Elle permet d'imager en 3D la positions des globules rouges en mouvement à partir d'un hologramme, ainsi que la structure 3D des vaisseaux sanguins perfusé à partir d'une séquence d'hologrammes.

The complete understanding of the mechanism driving colloid-polyelectrolyte complexation still represents a fundamental problem of great interest in soft matter. Polyelectrolyte adsorption onto oppositely charged surfaces represents the core of this problem and a number of theoretical studies, using different approaches, have been published on this subject.During the past few decades, colloid-multivalent ion complexation has been investigated by using either model systems, such as solid hard colloids, soft colloids of biological interests, or hydrophilic globular proteins6. In all cases two distinct but intimately related phenomena accompany and drive the self-assembly, i.e. charge-inversion and reentrant condensation.Although these phenomena have been observed in a variety of polyelectrolyte-colloid mixtures in different conditions, in all previously reported works the charge density on the colloid surface was fixed, or, at least, it could not be changed without changing the ionic strength or the pH of the suspending medium. Thermoresponsive microgels, whose synthesis is initiated by charged groups and is equivalent to an end-group functionalization, are characterized by a thermodynamic volume phase transition (VPT) that gives the opportunity to tune finely the adsorption of polyelectrolytes simply by changing temperature. Indeed, by controlling the particle volume, the VPT affects dramatically the microgel charge density and hence the polyelectrolyte adsorption.We investigated the complexation of thermoresponsive anionic poly(Nisopropylacrylamide) (PNiPAM) microgels and cationic -polylysine (epsilon-PLL) chains. By combining electrophoresis, light scattering, transmission electron microscopy (TEM) and dielectric spectroscopy (DS) we studied the adsorption of epsilon-PLL onto the microgel networks and its effect on the stability of the suspensions. We show that the volume phase transition (VPT) of the microgels triggers a large polyion adsorption. Two interesting phenomena with unique features occur: a temperature-dependent microgel overcharging and a complex reentrant condensation. The latter may occur at fixed polyion concentration, when temperature is raised above the VPT of microgels, or by increasing the number density of polycations at fixed temperature. TEM and DS measurements unambiguously show that short PLL chains adsorb onto microgels and act as electrostatic glue above the VPT. By performing thermal cycles, we further show that polyion-induced clustering is a quasi-reversible process: within the time of our experiments large clusters form above the VPT and partially re-dissolve as the mixtures are cooled down.Finally we give a proof that the observed phenomenology is purely electrostatic in nature: an increase of the ionic strength gives rise to the polyion desorption from the microgel outer shell. By showing that the VPT of thermoresponsive ionic microgels can be employed to trigger polyion adsorption and tune reentrant microgel condensation, our work lays the foundation for a groundbreaking strategy to tune electroadsorption ruled by temperature and that can be employed in a variety of fields spanning wastewater and soil remediation, nanoencapsulation of small charged nanoparticles, and selective drug delivery.

By combining rheology, light scattering, small angle X-ray scattering and simulations we explore the glassy dynamics of soft colloids using microgels and charged particles interacting by steric and screened Coulomb interactions, respectively. In the supercooled regime, the structural relaxation time (SRT) of both systems grows steeply with volume fraction, reminiscent of the behavior of colloidal hard sphere systems [1]. This suggests that softness has no impact on the growth of the SRT on approaching the glass transition, as confirmed by computer simulations. We show that the onset of a finite yield-stress, occurring within the supercooled regime, systematically corresponds to a minimum of the stretching exponent characterizing the decay of the two-time intensity autocorrelation function.Softness becomes relevant only at very large packing fractions, when the system falls out of equilibrium. In this non-equilibrium regime, the SRT depends surprisingly weakly on packing fraction and time correlation functions exhibit compressed exponential decays consistent with internal stress-driven relaxation. The transition to this novel regime coincides with the onset of an anomalous decrease of local order with increasing density, reminiscent of the reentrant glass transition predicted theoretically in ultrasoft systems [2,3], and corresponds to a weakening of the volume fraction dependence of the plateau modulus of the suspensions. We propose that these peculiar dynamics result from a competition between the non-equilibrium aging dynamics of the glassy state and the tendency of soft systems to refluidize at high packing fractions.