The Continuous Droplet Interface Crossing Encapsulation (cDICE) is an easy and robust method for producing, at high yield, monodisperse lipid vesicles with a controlled content as well as capsules with a designed shell. It consists in forcing a droplet through an interface between two imiscible fluids, using an external force such as centrifugation. At high inertia, the droplet entrain fluid that will constitute the shell of the capsule. At low inertia, the presence of amphiphile and the deformable interface interactions lead to monolayers zipping and formation of an amphiphile bilayer around the droplet. We will discuss the physical mechanisms involved in the production of both cDICE vesicles (low droplets inertia) and capsules (at high inertia), and the potential applications of this method. This method founds indeed many applications in biomimetics as it allows to encapsulate various biological solutions (biopolymers, hemoglobin, colloids, polymeric gels, cells. . . ) in membranes that can be composite and/or assymetric, or polymeric, and in the field of microencapsulation.

The Continuous Droplet Interface Crossing Encapsulation (cDICE) is an easy and robust method for producing, at high yield, monodisperse lipid vesicles with a controlled content as well as capsules with a designed shell. It consists in forcing a droplet through an interface between two imiscible fluids, using an external force such as centrifugation. At high inertia, the droplet entrain fluid that will constitute the shell of the capsule. At low inertia, the presence of amphiphile and the deformable interface interactions lead to monolayers zipping and formation of an amphiphile bilayer around the droplet. We will discuss the physical mechanisms involved in the production of both cDICE vesicles (low droplets inertia) and capsules (at high inertia), and the potential applications of this method. This method founds indeed many applications in biomimetics as it allows to encapsulate various biological solutions (biopolymers, hemoglobin, colloids, polymeric gels, cells. . . ) in membranes that can be composite and/or assymetric, or polymeric, and in the field of microencapsulation.

Polyion Complex (PIC) or Complex Coacervate Core (C3M) Micelles [1] have been used as structuring agents to template ordered mesostuctured porous silica materials [2]. PIC micelles assemble by electrostatic complexation of oppositely charged polyelectrolytes, one of them being a double hydrophilic block copolymer (DHBC). Compared to classical structuring agents obtained from amphiphilic molecules, PIC micelles offer several advantages: first, they can be recovered and reused in several mesoporous material synthesis cycles [2]. Secondly, they allow single step preparation of drug loaded porous materials [3]. Finally, tuning the characteristics of the porous material does no longer require the synthesis of new structuring agents: they can be adjusted by playing with the physico-chemical conditions, using a unique polyelectrolyte system. The present work aims at correlating the characteristics of the porous materials and the physico-chemical properties of the PIC micelles.Mesostructured materials have been prepared by condensation of TEOS in the presence of PIC micelles of polyethylene oxide-b-poly(acrylic acid) (POE-b-PAA) copolymer complexed with neomycin (NM) or oligochitosan (OC). TEM, sorption measurements and X-ray diffraction have shown that varying structures and pore sizes can be achieved by simply varying concentration and pH. On the other hand, using osmometry, specific ion potentiometry, elemental analysis and small angle X-ray scattering, the associative phase separation of poly(acrylic acid) in the presence of neomycin has been studied as a model system for the core of the PIC micelles.The hybrid materials obtained right after drying (without calcination) are porous. This is related to the high degree of swelling of the core of the PIC micelles that contains at least 50% of water in weight. The water content in the micelles varies with concentration because it is determined by osmotic equilibrium between the core and the suspending solution. This translates into variation of porous volume and allows fine tuning of the pore size in the hybrid material. These features are preserved after calcination. Finally, the pH of material synthesis has been shown to determine the drug loading: neomycin concentration in the hybrid porous material increases as pH increases.In conclusion, PIC micelles offer numerous advantages and opportunities in the domain of functional ordered mesostructured materials due to the sensitivity of their characteristics to physico-chemical parameters, allowing the reversibility of their assembling in water, the possible delivery of functional molecules and the possibility to control the swelling of PIC micelles core.References: [1] Voets, I. K.; de Keizer, A.; Stuart, M. A. C. Adv. Colloid Interface Sci., 2009, 147-48, 300-318.[2] Baccile, N.; Reboul, J.; Blanc, B.; Coq, B.; Lacroix-Desmazes, P.; In, M.; Gerardin, C. Angew. Chem. Int. Ed., 2008. 47(44), 8433-8437.[3] Molina, E.; Warnant, J.; Mathonnat, M.; Bathfield, M.; In, M.; Laurencin, D.; Jérôme, C.; Lacroix Desmazes, P.; Marcotte, N.; Gérardin, C. Langmuir, 2015. 31, 12839-12844.

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.

Dynamics of anisotropic particles at a fluid interface governs trapping and particles subsequentassembly. Measuring and controlling this viscous dynamics open the way to new materials [1], andapplications [2]. Despite these domains of applications, measurements of the viscous coefficient ofanisotropic particles were mainly restricted to the bulk [3-4] or in quasi-2D confinement between twoglass plates [5]. Here we measure the complete set of viscous coefficients of single micrometricprolate ellipsoids near and trapped at an air-water interface. These coefficients are obtained from theBrownian motion of the particle coupling interferometry and particle tracking. For particles trapped atthe interface we measured anomalously large drags even larger than in the bulk water (ratio of surface/bulk rotational drags rR > 1 in Figure) [6]. Such an intriguing behaviour is discussed in terms ofadditional random forces due to thermally activated fluctuations of the interface and their coupling tothe particle drag through the fluctuation–dissipation theorem.Figure: Rotational viscous-drag ratio rR (surface/bulk) of polystyrene ellipsoidal particles at anair/water interface versus particle’s aspect ratio φ. Inset: mean square angular displacements (MSADs)versus the time lag τ.[1] M. Cavallaro, L. Botto, E. Lewandowski, M. Wang, and K. Stebe, PNAS 108, 20923 (2011).[2] Z. Huang, D. Legendre, and P. Guiraud, Chem. Eng. Sci. 66, 982 (2011).[3] D. Mukhija and M. Solomon, J. Colloid Interface Sci. 314, 98 (2007).[4] T. H. Besseling, M. Hermes, A. Kuijk et al., Journal of Physics: Condensed Matter 27, 194109 (2015).[5] Y. Han, A. Alsayed, M. Nobili, J. Zhang, T. Lubensky, and A. Yodh, Science 314, 626 (2006).[6] G. Boniello, C. Blanc, D. Fedorenko, M. Medfai, N. Ben Mbarek, M. In, M. Gross, A. Stocco, M. Nobili,Nature Materials 14, 908 (2015).

The interface between a liquid and a fluid affects dramatically both the interactions and the motion of colloidal particles. In this talk, the impact of partial wetting dynamics on the motion of passive and active colloids will be presented. First, experimental results on the Brownian dynamics of micrometric spherical silica colloids andpolymeric ellipsoids trapped at a planar air-water interface will be described. Partial wetting defines a contact angle which sets the immersion depth of the colloid. Particle motion is confined in the interfacial plane. For spherical colloids, the contact angle is finely tuned in the range 30°-140° by surface treatments and measured in situ. Translational and rotational diffusion coefficients of colloids trapped at the water interface are obtained by particle tracking video-microscopy. Counter-intuitively, the friction felt by the colloid increases when the contact angle increases; i.e. when particles are less immersed in water and more in air, which has a negligible viscosity. To explain the slowing down of the translational motion for spheres and rotational diffusion for ellipsoids, an extra friction term originating from contact line fluctuations will be introduced.The second part of the talk deals with the motion of isolated active Janus colloids at the surface of water. Spherical catalytic Janus colloids have been prepared coating half surface of silica particles by a thin platinum layer. Immersion depth of the Janus colloids as well as their orientation with respect to the water surface reveal thecomplex wetting properties of Janus particles. The active motion of Janus colloids at the interface in the presence of various concentration of hydrogen peroxide has been studied. The types of trajectories, directional and circular ones observed revealed the effective force and torque induced by the catalytic decomposition of H2O2. At the water surface, active colloids perform more persistent directional motions as compared to the motions performed in the bulk. This has been interpreted as due to the loss of degrees of freedom resulting from the confinement at interfaceand also to the partial wetting conditions that possibly bring new contributions to the rotational friction at interface.