Polystyrene core-shell particles

Fig. 12 Left. Conventional core-shell particle from classical radical polymerization. Middle-. PolyAA-h-polyBA-h-polystyrene core-shell particles obtained after switching from a BA to a styrene feed in emulsion polymerization using polyAA macroRAFT agent. Right. TEM image of polystyrene domains stained with ruthenium tetroxide. From [110], with permission from the American Chemical Society...

Preparation of Lead Sulfide-Coated Polystyrene Core-Shell Particles... 

S. Gu, J. Onishi, E. Mine, Y. Kobayashi, M. Konno, Preparation of multilayered gold-silica-polystyrene core-shell particles by seeded polymerization,/. Colloid Inter/. Sci. 2004, 279,284-287. 

These 50 50 polybutyl acrylate-polystyrene core-shell particles showed interesting morphological changes upon ageing. All three latexes comprised spherical particles and formed continuous... 

For the characterization of Langmuir films, Fulda and coworkers [75-77] used anionic and cationic core-shell particles prepared by emulsifier-free emulsion polymerization. These particles have several advantages over those used in early publications First, the particles do not contain any stabihzer or emulsifier, which is eventually desorbed upon spreading and disturbs the formation of a particle monolayer at the air-water interface. Second, the preparation is a one-step process leading directly to monodisperse particles 0.2-0.5 jim in diameter. Third, the nature of the shell can be easily varied by using different hydrophilic comonomers. In Table 1, the particles and their characteristic properties are hsted. Most of the studies were carried out using anionic particles with polystyrene as core material and polyacrylic acid in the shell. 

Seeded polymerization using a slight amount of monomer leads to the surface modification without changing particle size. The resulting particles are a kind of core-shell particles or, more exactly, core-skin particles (Fig. 12.2.4C). Seeded polymerization of sugar-units-containing styrene derivative on polystyrene seed particle was carried out to obtain latex particles covered with sugar units (17). A necessary condition for this is that the monomer is more hydrophilic than the seed polymer. If not, the monomer permeates into the seed particle and only a small fraction remains on the... 

Core-shell nanoparticles can also be fabricated using microemulsions. This was performed using a two-stage microemulsion polymerization beginning with a polystyrene seed [62]. Butyl acrylate was then added in a second step to yield a core-shell PS/PBA morphology. The small microlatex led to better mechanical properties than those of similar products produced by emulsion polymerization. Hollow polystyrene particles have also been produced by microemulsion polymerization of MMA in the core with crosslinking of styrene on the shell. After the synthesis of core-shell particles with crosslinked PS shells, the PMMA core was dissolved with methylene chloride [63]. The direct cross-... 

The experimental details of dispersion polymerization with various polymeric dispersants and macromonomers are fairly well established. A basic expression for particle size control has also been derived for the formation of clear-cut core-shell particles based on highly incompatible core-shells such as polystyrene-PVP and polystyrene-PEO. However, results deviate considerably from theory in compatible polymers such as PMMA with PEO macromonomer. The detailed structures of the hairy shells need to be discovered in order to better understand the exact mechanism of their formation and stabilizing function. 

It must be noted that the process of seeded emulsion polymerization does not lead to an equilibrium structure. Hence, the sharp interface between PS and PMMA observed in the above core-shell particles cannot be explained by thermodynamic arguments. A possible mechanism maybe sought in the adsorption of oligo(methylmethacrylate) radicals from the water phase onto the PS-seed particles [45]. The temperature of the seeded emulsion polymerization (80 °C [45]) is well below the glass transition temperature of polystyrene and the adsorbed chains bear a sulfate endgroup. The adsorbed oligomers will therefore remain at the surface of the core particles and in consequence there is no extended interface between PS and PMMA in these. particles. 

Fig. 28 TEM images of (a) the polystyrene latex spheres used as the core and (b) the same particles coated with a thin 25 nm titania shell, (c) SEM image of hollow titania spheres obtained by calcination of the polystyrene/Ti02 core-shell particles at 600°C under ain (d) Eidaiged TEM view of some hollow titania particles showing the small anatase crystallites that compose the sheU. Reproduced from [231] with permission of the American Chemical Society...

The above synthetic strategy leads to easy generation of [R(Ag°)(Cu )] H and [R(Au°)(Pd°)] Cl nanocomposites with their inverted structures. The order of deposition of the bimetallic shells on the polystyrene beads can be altered by the successive immobilization of their corresponding precursors. Matrixes such as [R (Pd°)(Pt°)] Cl and [R(Ag°)(Au°)]+Cl were also synthesized from their corresponding metal chloride precursors. The layer-by-layer deposition technique has been widely used to fabricate core-shell particles because of its convenience to tailor the thickness and composition of the shells. The thickness can be controlled by varying the number of cycles of operation immobilization and subsequent reduction. In this way, we can deposit more than two metals on any kind of charged polystyrene bead. 

Figure 5. Themial gravimetric analysis showing loss of polystyrene from PbS/0.827 pm PS-CO2 core-shell particles.

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