Encapsulated silica particles

Choi, H.-H., Park, J., and Singh, R.K., Nanosized titania encapsulated silica particles using an aqueous TiC solution, Appl. Surf. Sci., 240, 7, 2005. 

Nemati F, Saeedirad R (2013) Nano-FCjO, encapsulated-silica particles bearing sulfonic acid groups as a magnetically separable catalyst for green and efficient synthesis of functionalized pyrimido[4,5-6]quinolines and indeno fused pyrido[2,3-[Pg.160]

As in the case of graphite-supported catalysts, some metal particles were also encapsulated by the deposited carbon (Fig. 4). However, the amount of encapsulated metal was much less. Differences in the nature of encapsulation were observed. Almost all encapsulated metal particles on silica-supported catalysts were found inside the tubules (Fig. 4(a)). The probable mechanism of this encapsulation was precisely described elsewhere[21 ]. We supposed that they were catalytic particles that became inactive after introduction into the tubules during the growth process. On the other hand, the formation of graphite layers around the metal in the case of graphite-supported catalysts can be explained on the basis of... 

Ow et al. (2005) developed an improved method of incorporating fluorescent molecules into silica particles using a modified Stober synthesis, which resulted in both enhanced fluorescence and photostability of the encapsulated dyes. In this two-stage procedure, reactive organic dyes... 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

Also, here, the effect of the adsorption layer of HPC on encapsulation of silica particles in polymerization of styrene in the presence of silica particles has been investigated. Encapsulation is promoted greatly by the existence of the adsorption layer on the silica particles, and the dense adsorption layer formed at the LCST makes composite polystyrene latices with silica particles in the core (7.). This type of examination is entirely new in polymer adsorption studies and we believe that this work will contribute not only to new colloid and interface science, but also to industrial technology. 

It was apparent that the dense adsorption layer of HPC which was formed on the silica particles at the LCST plays a part in the preparation of new composite polymer latices, i.e. polystyrene latices with silica particles in the core. Figures 10 and 11 show the electron micrographs of the final silica-polystyrene composite which resulted from seeded emulsion polymerization using as seed bare silica particles, and HPC-coated silica particles,respectively. As may be seen from Fig.10, when the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of silica particles, and indeed new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were generated. This indicated that the dense adsorption layer of HPC formed at the LCST plays a role as a binder between the silica surface and the styrene molecules. 

All these results indicate that the dense adsorption layer of HPC formed on silica particles at the LCST plays a very important role in the area of particle encapsulation. 

Sol-gel microencapsulation in silica particles shares the versatility of the sol-gel molecular encapsulation process, with further unique advantages. Sol-gel controlled release formulations are often more stable, potent and tolerable than currently available formulations. The benefits of microencapsulation can be customized to deliver the maximum set of benefits for each active ingredient. Overall, these new and stable combinations of active pharmaceutical ingredients (APIs) result in improved efficacy and usability. 

FIGURE 4.5 Chromatograms of a-phenylethanol enantiomers nsing (a) SFC and (b) open tubular column GC. Conditions (a) 12 cmx250 p.m ID capillary packed with 5-p.m porous (300 A) silica particles encapsulated with fS-CD polymethylsiloxane (10% w/w) and end-capped with HMDS, 30°C, 140 atm, CO2, FID, 10 cmxl2 p.m ID restrictor, (b) 25 mx250 p.m ID cyano-deactivated capillary cross-linked with fi-CD polymethylsiloxane (0.25 xm df) 130°C He FID. (Reprinted from Wu, N. et al. 2000. J. Microcol. Sep. 12 454-461. With permission.)... 

Figure 10 Size-dependence of the melting point and diffusion coefficient of silica-encapsulated gold particles. The dotted curve is calculated by the equation of Buffat and Borel. The bulk melting temperature of An is indicated by the double arrow as (oo). The solid curve (right-hand side axis) is a calculated An self-diffusion coefficient. (From Ref. 146.)...

Another type of dendrimer, that has been used to encapsulate Au32 particles is hydroxyl-terminated fifth-generation dendrimers (G5-PAMAM). The particles were adsorbed on silica (0.3wt.% Au),108 and after washing and removal of the dendrimer under oxygen at 573 K, followed by reduction under hydrogen at 573 K, the supported gold particles were even larger than above (14.5 nm), probably because silica is not a support that easily leads to small particles. 

Silica nanoparticles are also hydrophilic and have therefore to be functionalized prior to encapsulation. Without functionalization, the negatively charged silica particles can be used as Pickering stabilizers, leading to hybrid nanoparticles with silica located on the surface of the nanoparticles (see Fig. 13a) [100]. 

Besides styrene, MMA, BA, or their copolymers, and also less commonly used polymers such as poly(styrenesulfonic acid) (PSSA), poly (hydroxyethylmethacrylate) (PHEMA), poly(aminoethylmethacrylate) PAEMA [111], polyethylene (PE) [112], or polyamides [113], were used for the encapsulation of the silica, as reported in the literature. Polyethylene [112] could also be obtained as encapsulating polymer if a nickel-based catalyst which is dispersed in the aqueous continuous phase is used. Here, lentil-shaped hybrid particles with semicrystalline polyethylene or isotropic hybrid particles with amorphous polyethylene are detected. Silica/polyamide hybrid nanoparticles were synthesized by miniemulsifying a dispersion consisting of 3-aminopropyl triethoxysilane (APS) modified silica particles and sebacoylchloride [113] in an aqueous continuous phase where hexamethylene diamine is dropwise added. 

The immense versatility of the sol-gel process in liquid phase enables control on the size, porosity, surface area, morphology (full or core-shell particle), and hydrophilic-lipophilic balance of the encapsulating silica cage. Not only the conditions of the process can be controlled... 

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