Templated Surface Sol–Gel Synthesis of SiO₂ Nanotubes and SiO₂‐Insulated Metal Nanowires

Abstract

slightly changed after their incorporation in polymer matrices, the optical properties of the resulting composites are, in principle, determined by the properties of the initial CdTe nanocrystals in solution. Therefore, this new synthetic route opens up an alternative method to produce highly fluorescent CdTe±polymer composites with predictable properties. Moreover, the fluorescent microbeads of nanocrystal±polymer composite could find application in biological labeling. [8b] Further attempts are underway to produce micrometer-sized CdTe±PS beads by swelling crosslinked PS beads in a solvent mixture containing OVDAC-coated CdTe and styrene, and followed by the polymerization of composite CdTe nanocrystals in the swollen PS beads. ExperimentalA series of aqueous colloidal CdTe solutions were prepared by adding freshly prepared NaHTe solution to 1.25 10 ±3 N N 2 -saturated CdCl 2 solutions at pH 9.0 in the presence of 3-mercaptocarboxylic acid (MPA) as a stabilizing agent [5,19]. The molar ratio of Cd 2+ /MPA/HTe ± was fixed at 1:2.4:0.5. The resulting mixture was then subjected to reflux that controlled the growth of the CdTe nanocrystals. Octadecyl-p-vinylbenzyldimethylammonium chloride (OVDAC) was synthesized according to the procedure reported by Aoyagi et al. [23] and dissolved in styrene at a concentration of 2 mg mL ±1 . 10 mL of OVDAC styrene solution was added to 20 mL of CdTe aqueous solution under vigorous stirring. The styrene phase was then separated and polymerized in a glass tube in an oil bath at 72~74 C for 30 h using 0.2 wt.-% azobisisobutyronitrile (AIBN) as initiator. Transparent CdTe±polystyrene composites resulted. For more quantitative syntheses, chloroform was used instead of styrene. Powders of the OVDAC-coated CdTe was obtained after evaporation of chloroform and a drying process. Then the composite nanocrystals were redispersed quantitatively (from 0.1 wt.-% to 10 wt.-%) in styrene, which was followed by freeradical polymerization initiated by 0.2 wt.-% AIBN in an oil bath. CdTe±poly-styrene/poly(methyl methacrylate) (PS/PMMA) composites were obtained in a similar way by dispersing CdTe±OVDAC in the mixture of methyl methacrylate and styrene with 10:1 volume ratio. The concentration of AIBN is 0.1 wt.-% in the following polymerization which was realized by a programmed heating process from 50 to 80 C.The relative PL quantum yields of all CdTe samples were estimated using Rohodamine 6G as PL reference [5,19]. For the measurement of PL quantum yield of CdTe in PS composites, composite plates were fabricated using a planar chamber as the polymerizing mode. The concentration of the inorganic nanocrystals in the polymer composites was characterized by thermogravimetric analysis (TGA), which was performed on a Mettler Netzsch STA 449C thermoanalysis instrument (Analyses were carried out under N 2 flow in the range of 30±800 C with heating rate of 20.0 C min ±1 ). For the CdTe±PS composite samples containing 10 wt.-% CdTe±OVDAC composites, the concentration of inorganic CdTe was around 3 wt....

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