Ludox silica nanoparticles

Fig. 10 TEM images (scale bars. 100 nm) of (a) PMMA latex armored with Ludox silica nanoparticles. Multilayered nanocomposite polymer colloids with (b) a hairy outer layer of polyacrylonitrile, and (c) a soft shell of poly(n-butyl acrylate). Reproduced from [66] with permission of American Chemical Society...

Chiral phospholipid molecules aggregate spontaneously to form tubes with diameters of 500 nm and lengths of 50-100 pm. Diacetylenic phosphatidylcholine structures were first coated in 1993 by Baral and Schoen [72] with silica nanoparticles. The tubule dispersion was mixed with Ludox (a silica sol with a particle diameter of 10-15 nm and negative surface charge at pH 8.2) and allowed to stand for up to 9 days, during which time a white precipitate formed. TEM analysis of the collected precipitate showed a film with a thickness of about 50 nm, composed of silica particles, on the hollow cylindrical templates. The adsorption of the nanoparticles to the headgroups of the phospholipid is believed... 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

Ma and Dai [121] reported the synthesis of polystyrene latexes armored with silica nanoparticles (10-15nm in diameter, PA-ST silica sol, Nissan Chemicals) via solids-stabilized emulsion polymerization. They used VA-086, 2,2 -azobis [2-methyl-lV-(2-hydroxyethyl)propionamide], as nonionic initiator. Whereas we found that Pickering emulsion polymerization of styrene using Ludox TM-40 and a low flux of radicals generated from potassium persulfate did not result in an armored latex, the hydroxyethyl groups probably enhance the wettability of the surface of the latex particles to promote silica adhesion. This was confirmed by a... 

In our laboratory, we have recently conducted gelation studies of silica nanopardcles in microgravity during the STS-95 space shuttle mission (28). Stable silica nanoparticle dispersions may be form either by polymerization of silicic acids in an aqueous system or through hydrolysis and condensation of silicon alkoxides (the sol-gel or Stober route). Comparison of small-angle x-ray scattering (SAXS) measurements of Ludox, a commercial aqueous silicate with acid- and base-catalyzed alkoxides shows that only aqueous silicate sols are uniform, whereas alkoxides generate fractal particles. As Brinker and Scherer point out (29), these results illustrate that sols derived from aqueous silicates are... 

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