l-Arginine-Catalyzed Synthesis of Nanometric Organosilica Particles through a Waterborne Sol-Gel Process and Their Porous Structure Analysis.

We report an efficient and easy-to-implement waterborne sol-gel process for the synthesis of nanometric organosilica particles. In this process, tetraethyl orthosilicate (TEOS) and 3-(methacryloxy)propyl trimethoxy silane (γ-MPS), employed as silica sources, were heterogeneously delivered in an aqueous solution of l-arginine, a basic amino acid used as a catalyst, from a top organic layer. Co-condensation of TEOS with γ-MPS led to the formation of organosilica particles with diameters between 30 and 230 nm when increasing the γ-MPS content from 0 to 10.1 mol % in the silica source. Nitrogen sorption analyses confirmed the microporous nature of the obtained particles after calcination. The Brunauer-Emmett-Teller (BET) surface areas increased from 27 (before calcination) to 684 m2 g-1 (after calcination) for the organosilica particles containing 10.1 mol % of γ-MPS. Fourier transform infrared spectroscopy and 29Si NMR were employed to analyze the chemical structure of the organosilica spheres and provide insight into the mechanism of particle formation. In the second part, hybrid organosilica particles with a core-shell morphology were synthesized through the combination of Pickering emulsion and the sol-gel process. γ-MPS emulsion droplets stabilized by tiny silica particles (formed in a separate step) were first generated and used as seeds to grow a silica shell on their surface through TEOS addition from the top organic layer. Transmission electron microscopy and pore size analyses of the resulting particles after calcination revealed a unique dual-porosity structure with a mesoporous inner core and a micro/mesoporous silica shell with ink-bottle-type pores.

Silica encapsulation by miniemulsion polymerization: distribution and localization of the silica particles in droplets and latex particles.

The impact of including hydrophobically modified silica on the morphology of miniemulsified monomer mixtures and that of the resulting polymer particles was investigated, with emphasis placed on the distribution and localization of the inorganic phase. Silica nanoparticles with diameters of 20 and 78 nm were first modified with γ-methacryloxypropyl trimethoxysilane (γ-MPS) to favor their dispersion in methyl methacrylate (MMA)/n-butyl acrylate (BuA) and mixtures of varying MMA to BuA weight ratios. The monomer-silica dispersions were then emulsified by ultrasonication, and the resulting silica-loaded droplets were examined using cryo-transmission electron microscopy (cryo-TEM). This represents the first time such silica-loaded nanodroplets were examined in this way. The results of the cryo-TEM show that whereas the silica particles could easily be dispersed in MMA or a mixture of MMA and BuA to produce stable dispersions, the emulsification step promotes the (re)localization of the silica at the oil-water interfaces. It was also shown that not all droplets are equal; some droplets and particles contain no silica whereas others contain many silica particles. After the subsequent polymerization step, the silica was buried inside the latex particles.

Synthesis of SiO2-coated Bi2S3/poly(styrene) nanocomposites by in-situ polymerization.

New nanocomposites containing silica-coated Bi2S3 nanofibers were synthesised by in situ polymerization using two distinct synthetic strategies: emulsion and suspension polymerization. Transmission and scanning electron microscopy of the nanocomposite particles showed that in both cases the Bi2S3/SiO2 nanoparticles were densely coated with poly(styrene). In situ emulsion polymerization afforded nanocomposites in which the nanofibers were coated with polymer spheres whilst suspension polymerization gives rise to a homogeneous polymer layer coat. The morphology of the poly(styrene) coating observed is discussed considering the surface modification of the nanofibers and the polymerization technique involved.

Implementation of a new Cryopad on the diffractometer POLI at MLZ.

A new polarized neutron single crystal diffractometer POLI (Polarization Investigator) has been developed at the Maier-Leibnitz Zentrum, Garching, Germany. After reviewing existing devices, spherical neutron polarimetry has been implemented on POLI as a main experimental technique using a third-generation cryogenic polarization analysis device (Cryopad) built in cooperation between RWTH University and Institut Laue-Langevin. In this report we describe the realization and present the performance of the new Cryopad on POLI. Some improvements in the construction as well as details regarding calibrations of Cryopad and its practical use are discussed. The reliable operation of the new Cryopad on POLI is also demonstrated.

Organic-inorganic nanostructured colloids.

The synthesis and applications of organic-inorganic nanostructured colloids and colloidal-based materials are reviewed here. Emphasis is placed on the strategies and synthetic methods developed to organize organic-inorganic architectures. The article begins with a description and a general hierarchical classification of different systems, from inorganic particle synthesis and surface modification to more elaborate nanostructured colloids obtained through in situ encapsulation and/or self-assembly techniques. Ordering of colloids into two- and three-dimensional arrays and their use as templates is also considered. For every system, typical examples are given that highlight the advantages and limitations of the techniques, as are more recent developments. Some properties and applicability of organic-inorganic colloids in catalysis, medicine, and coating technologies are also cited.

Use of silica particles for the formation of organic-inorganic particles by surfactant-free emulsion polymerization.

Polystyrene/silica (PS/SiO(2)) and poly(styrene-co-methyl methacrylate)/SiO(2) composite latex particles were prepared by surfactant-free emulsion polymerization in the presence of a poly(ethylene glycol) monomethylether methacrylate (PEGMA) macromonomer. The resulting composite particles were stabilized by the negatively charged silica particles that adhered to the surface of the latex particles. Different process parameters were investigated in order to optimize the latex stability and maximize the reaction rate. Mixing in such a surfactant-free process is of major importance and is mainly determined by the type of impeller used during the emulsification. The concentrations of PEGMA and silica particles were also optimized in order to improve the interaction between the organic and inorganic phases and ensure a good latex stability. The presence of silica particles on the polymer particle surface was found to affect radical absorption and decrease therefore the reaction rate.

Encapsulation of Inorganic Particles by Dispersion Polymerization in Polar Media.

Following a previous work (Bourgeat-Lami, E., and Lang, J., J. Colloid Interface Sci. 197, 293 (1998)), encapsulation of silica beads has been achieved by dispersion polymerization of styrene in an aqueous ethanol medium using poly(N-vinyl pyrrolidone) as stabilizer. Silica beads, prepared according to the Stöber method, were coated prior to polymerization by grafting 3-(trimethoxysilyl)propyl methacrylate onto the surface. A great number of silica beads per composite particle were previously found using beads that had diameters between 49 and 120 nm. In the present work, larger silica beads with diameters between 191 and 629 nm are investigated. We demonstrate by transmission electron microscopy that, consequently, only a small number of silica beads are contained in the composite particles. By counting the composite particles containing precisely zero, one, two, three, four, and more than four silica beads, it clearly appears that the encapsulation of only one silica bead can be obtained simply by increasing the size of the beads. Under our experimental conditions, the optimal bead diameter for achieving composite particles containing only one silica bead turns out to be around 450 nm. We show that increasing the silica bead size above this value results in an increased number of composite particles without silica beads. In contrast, the number of composite particles with two, three, four, or more than four silica beads increases with decreasing silica bead size. In addition to the above variations in composition of the composite particles, changes in particle shapes were also observed as a function of the size of the silica beads and the styrene concentration in the polymerization medium. Hypotheses concerning these variations are presented. Copyright 1999 Academic Press.

Encapsulation of Inorganic Particles by Dispersion Polymerization in Polar Media

Polymer encapsulation of small silica particles, using dispersion polymerization of styrene in aqueous ethanol medium with poly(N-vinyl pyrrolidone) (PVP) as stabilizer, is described. Silica particles, directly synthesized by the Stober process in an aqueous ethanol medium, are either unreacted (hydrophilic character) or coated with 3-(trimethoxysilyl)propyl methacrylate (MPS) (hydrophobic character), which is grafted at the silica particle surface. When the bare silica particles are used as the seed, there is a strong tendency of the silica beads to cover the surface of the polystyrene particles and obviously encapsulation does not occur. On the contrary, when the silica surface is made hydrophobic by coating, the inorganic particles are entirely contained in the polystyrene particles as evidenced by microscopy techniques (TEM, SEM, AFM). It is shown that some polystyrene chains are then chemically bonded to the silica particles, through the coupling agent MPS, and that only a small amount of bonded polystyrene, compared to the total polystyrene synthesized, is sufficient to obtain encapsulation of the silica particles with the entire amount of polystyrene synthesized during the polymerization. Under our experimental conditions, each polystyrene latex particle contains, on average, 4 to 23 silica beads depending, in particular, on the size of the silica. We believe that it is possible to control the composite particle size and morphology by a convenient choice of the composition of the system. Moreover, this new polymer-encapsulation process could be used to synthesize other organic-inorganic composite particles, using, for example, other monomers or minerals. Copyright 1998 Academic Press. Copyright 1998Academic Press