Emulsions Stabilized with Alumina-Functionalized Mesoporous Silica Particles.

Alumina-functionalized ordered mesoporous silica SBA-15 particles have been proposed to stabilize Pickering emulsions. Functionalization of SBA-15 particles have been performed by depositing alumina using a two-step synthesis (first, silica condensation, followed by alumina precipitation). Three different Al to Si ratios have been prepared. The calcined materials have been characterized by TEM, SEM, XRD, N2 physisorption, and zeta potential, in order to determine key physicochemical properties, and the alumina localization. The emulsifying and stabilizing properties of the calcined particles have been evaluated for water/toluene-based Pickering emulsions.

Hybrid Core-Shell Nanoparticles by "Plug and Play" Self-Assembly.

Supramolecular hybrid functional nanoparticles (NPs) can be obtained via the colloidal tectonics approach provided that multiple interactive molecular tectons are used. Herein, the programmable synthesis of novel hybrid core-shell nanoparticles via the following sequential steps is reported: (i) complexation of 1-decanol by the ß-cyclodextrin (ß-CD), (ii) spontaneous self-assembly into CD NPs, (iii) adsorption of polyoxometalate anions, PW12 O40 3- , on the polar neutral interface of the CD NPs. Such an approach paves the way for the design of novel and original materials and systems.

Dense covalent attachment of magnetic iron oxide nanoparticles onto silica particles using a diazonium salt chemistry approach.

We demonstrate that the reaction of amino modified particles with tert-butylnitrite can provide diazonium surface functionality which itself is highly reactive with iron oxide nanoparticles in basic media. Using this strategy we synthesize a magnetic hybrid material with dense covalent attachment of magnetic iron oxide nanoparticles on the silica surface. This simple and versatile functionalization procedure has a wide variety of potential applications in surface science and materials research.

Fine tuning of emission through the engineering of colloidal crystals.

We describe the preparation and characterization of photonic colloidal crystals from silica spheres with incorporated luminescent [Mo(6)Br(14)](2-) cluster units. These structures exhibit strong angle-dependent luminescent properties. The incorporation of one or several planar defects in the periodic structures gives rise to the creation of a passband in the stopband. In the energy range of this passband, an increase of the emission intensity has been found.

Nonaqueous sol-gel chemistry applied to atomic layer deposition: tuning of photonic band gap properties of silica opals.

Combining both electromagnetic simulations and experiments, it is shown that the photonic pseudo band gap (PPBG) exhibited by a silica opal can be fully controlled by Atomic Layer Deposition (ALD) of titania into the pores of the silica spheres constituting the opal. Different types of opals were assembled by the Langmuir-Blodgett technique: homogeneous closed packed structures set up of, respectively, 260 and 285 nm silica spheres, as well as opal heterostructures consisting of a monolayer of 430 nm silica spheres embedded within 10 layers of 280 nm silica spheres. For the stepwise infiltration of the opals with titania, titanium isopropoxide and acetic acid were used as metal and oxygen sources, in accordance with a recently published non-aqueous approach to ALD. A shift of the direct PPBG, its disappearance, and the subsequent appearance and shifting of the inverse PPBG are observed as the opal is progressively filled. The close agreement between simulated and experimental results is striking, and promising in terms of predicting the properties of advanced photonic materials. Moreover, this work demonstrates that the ALD process is rather robust and can be applied to the coating of complex nanostructures.

Multiresponsive hybrid microgels and hollow capsules with a layered structure.

Various stimuli-responsive composite particles with a high control of their internal structure and their corresponding hollow capsules are synthesized and characterized by photon correlation spectroscopy, TEM, and AFM. Core-shell particles with a silica core and a thermoresponsive shell are obtained by polymerization of N-isopropylacrylamide (NIPAM) in the presence of silica seeds grafted with a high density of gamma-methacryloxypropyltrimethoxysilane (MPS). The influence of the synthesis conditions is studied. The shell thickness increases when the monomer concentration increases in a limited range where uniform composite particles with a single core are obtained. At constant monomer concentration, the shell thickness does not depend on the size of the silica seeds, but the presence of free unbound microgels is observed when the silica surface area decreases. A range of particle diameters and shell thicknesses is thus obtained, which can lead to the corresponding hollow capsules by exposure to hydrofluoric acid solution. The volume phase transition temperature of these materials can be easily tuned by replacing the NIPAM monomer by another N-alkylacrylamide derivative. However, the incorporation of comonomers such as acrylic acid (AA) and a phenylboronic acid (PBA) derivative inhibits the formation of core-shell structures. In order to get pH or glucose responsiveness, these functional groups can be incorporated in the outer shell of a core-double shell structure, with pNIPAM as intermediate shell. pH-responsive and glucose-responsive composite particles are obtained by this method with a high control of their internal structure.

Pickering emulsions with stimulable particles: from highly- to weakly-covered interfaces.

We study oil-in-water emulsions stabilised by pH-sensitive colloidal silica or latex particles. Depending on the composition of the continuous phase, the same type of particles and the same emulsification process lead to emulsions characterised either by large drops densely covered by the particles, or to small droplets which are weakly covered. The two kinetically stable states can be tuned reversibly by using pH or salinity as compositional stimuli. We examine the emulsions' behaviour in these two limiting cases and we discuss the possible mechanisms allowing stabilisation, especially in the case of low surface coverage.