Preparation of porous thin-film polymethylsiloxane microparticles in a W/O emulsion system

Porous thin-film polymethylsiloxane microparticles have been prepared successfully from octyltrichlorosilane and methyltrichlorosilane in (water/oil) W/O emulsion systems by using several oil phases and changing the amount of the silanes or of the surfactant Span 60. Hollow microspheres of various shell thicknesses (120-180 nm) and high surface area were prepared by using four types of nonpolar solvents as the oil phase of the W/O emulsion system. The diameter of the spheres can also be controlled (1-1.6 mu m) by using different oil phases. The results of thermal analysis, nitrogen adsorption isotherm, infrared spectra and X-ray diffraction data showed that hollow microspheres of amorphous polymethylsiloxane with high surface area (360-385 m(2)g(-1)) can be obtained by heating the spheres in air at 673 K; the polymethylsiloxane microspheres become nonporous silica particles after calcination at 873 K for 3 h. Cup-shape microparticles of polymethylsiloxane with nano-order thickness (20-120 nm) were prepared by reducing the amount of silanes in the mixture. Small hollow particles were prepared by replacing a portion of the octyltrichlorosilane with Span 60.ArticlePOLYMER JOURNAL. 47(6): 449-455 (2015)journal articl

Magnetic Rattle-Type Core–Shell Particles Containing Iron Compounds with Acid Tolerance by Dense Silica

Magnetic rattle-type particles, comprising magnetite or metallic iron in nonporous dense hollow silica microspheres, were fabricated by using sol–gel reactions of alkylsilyl trichlorides around droplets of aqueous iron nitrate solution in a water-in-oil emulsion. After evaporation of water within the silica capsules to leave iron salts, calcination of the dried sample was conducted to transform into a hematite (α-Fe₂O₃) core and porous hollow silica shell by losing alkyl groups of polyalkylsiloxane. Hydrogen gas penetrated through the silica shell and reduced hematite to magnetite (Fe₃O₄) at 310 °C and metallic iron (α-Fe) at 450 and 500 °C. The reduction at 310 °C resulted in largest magnetization at 12 kOe among the present magnetic particles. The core magnetic compounds were enclosed by a dense silica shell, which was transformed from porous silica by annealing in nitrogen at 700 °C. Because the magnetic particles were encapsulated by the dense silica shell, the magnetism was shown even after immersion in 1 M HCl for a longer period. Acidity was successfully imparted on this magnetic capsule by anchoring sulfonic groups covalently for its use as magnetically collectable solid acid