Transformation of highly ordered large pore silica mesophases (Fm3m, Im3m and p6mm) in a ternary triblock copolymer-butanol-water system

Exceptional control of the phase behavior of highly ordered large pore mesostructured silica (with the choice of Fm3m, Im3m or p6mm symmetry) is achieved using a triblock copolymer (EO(106)PO(70)EO(106)) and butanol at low acid concentrations.     

Controlled polymerization in mesoporous silica toward the design of organic-inorganic composite nanoporous materials

Free-radical polymerization inside mesoporous silica has been investigated in order to open a route to functional polymer-silica composite materials with well-defined mesoporosity. Various vinyl monomers, such as styrene, chloromethyl styrene, 2-hydroxyethyl methacrylate, and methacrylic acid, were polymerized after impregnation into mesoporous silicas with various structures, which were synthesized using polyalkylene oxide-type block copolymers. The location of the polymers was systematically controlled with detailed structures of the silica framework and the polymerization conditions. Particularly noteworthy is the polymer-silica composite structure obtained by in situ polymerization after the selective adsorption of monomers as a uniform film on silica walls. The analysis of XRD data and the N(2) adsorption isotherms indicates the formation of uniform polymer nanocoating. The resultant polymer-silica composite materials can easily be post-functionalized to incorporate diverse functional groups in high density, due to the open porous structure allowing facile access for the chemical reagent. The fundamental characteristics of the composite materials are substantiated by testing the biomolecule's adsorption capacity and catalytic reactivity. Depending on the structure and composition of polymers, the resultant polymer-silica composite materials exhibit notably distinct adsorption properties toward biomolecules, such as proteins. Furthermore, it is demonstrated that the nanocoatings of polymers deposited on the mesopore walls have remarkably enhanced catalytic activity and selectivity, as compared to that of bulk polymer resins. We believe that, due to facile functionalization and attractive textural properties, the mesoporous polymer-silica composite materials are very useful for applications, such as adsorption, separation, host-guest complexes, and catalysis.     

Immobilizing a Fluorescent Dye Offers Potential to Investigate the Glass/Resin Interface

Silane coupling agents are commonly applied to glass fibers to promote fiber/resin adhesion and enhance durability in composite parts. In this study, a coupling agent multilayer on glass was doped with trace levels of the dimethylaminonitrostilbene (DMANS) fluorophore. The fluorophore was immobilized on the glass surface by tethering the molecule to a triethoxy silane coupling agent, creating the DMANS/silane coupling agent molecule (DMSCA). DMSCA was then diluted with commonly used coupling agents and grafted to a glass microscope coverslip to create a model composite interface. A 53-nm blue shift in fluorescence from the immobilized DMSCA can be followed during cure of an epoxy resin overlayer, giving this technique potential to monitor the properties of the fiber/resin interface during composite processing. Contact angle measurements on these coupling agent layers were similar in the presence or absence of the DMSCA molecule, suggesting that trace levels of the fluorescent probe did not affect the structure of the layer. The immobilized DMSCA molecule behaved similarly to the DMANS precursor in solution. Both showed longer wavelength fluorescence in more polar environments. Copyright 2000 Academic Press.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Electrostatically stabilized metal oxide particle dispersions in carbon dioxide

We report electrostatic stabilization of micrometer-sized TiO(2) particles at long range (several micrometers) in liquid and supercritical CO(2) despite the ultralow dielectric constant, as low as 1.5. The counterions were solubilized in dry reverse micelles, formed with a low-molecular weight cationic perfluoropolyether trimethylammonium acetate surfactant, to prevent ion pairing with the particle surface. Dynamic light scattering and settling velocities indicate a particle diameter of 620-740 nm. The electrophoretic mobility of -2.3 x 10(-8) m(2)/V s indicated a particle charge on the order of -1.7 x 10(-17) C, or 105 elementary negative charges per particle. The balance of particle compression by an electric field versus electrostatic repulsion generated an amorphous arrangement of particles with 5-9 mum spacing, indicating Debye lengths greater than 1 mum. Scattering patterns also indicate that chains of particles may be achieved in CO(2) by dielectrophoresis with alternating fields. The electrostatic stabilization has been achieved by solubilizing a small concentration of counterions in only a small fraction of the reverse micelles in the double layer. Whereas many low-molecular weight surfactants have been shown to form reverse micelles in CO(2), very few polymers are able to stabilize micrometer-sized colloids sterically. Thus, electrostatic stabilization has the potential to expand markedly the domain of colloid science in apolar supercritical fluids.