Magnetic polystyrene particles

Fig. 19 TEM image of raspberry-like magnetic polystyrene particles. Reprinted from [160] with permission...

Mori and Kawaguchi reported the preparation of magnetic polystyrene particles containing 30 wt% of magnetite. Magnetic polystyrene particles of 300 nm were produced and easily separated when persulphate, KPS or APS initiator was used. Conversely, due to high colloidal stability, the latex prepared by oil-soluble initiator (for instance AIBN) was not easy to separate, and the magnetite nanoparticles were located on the surface of the polystyrene latex. A mixture of initiators resulted in intermediate properties compared to individual systems [170]. 

Figure 2.16 Transmission electron micrograph of magnetic polystyrene particles.

FIGURE 6.1 (a) TEM micrographs of magnetic polystyrene particles (R0039, Merck). The small magnetic... 

The magnetic polystyrene latex particles with diameter of 120 nm were covered by PNIPA gel layer. The mPS latex prepared according to the procedure described previously was strongly stirred at 60 °C and kept under N2 atmosphere for 1 h. Then, 0.05 g APS and 0.5 mL 1 M NIPA solution were added to the mPS latex and the reaction mixture was stirred at 60 °C for more than 1 h. Then, 0.5 mL 1 M NIPA solution and 0.36 mL 0.1 M BA solution were added. After 2 h, 0.5 mL 1 M NIPA solution and 0.36 mL 0.1 M BA solution were added again to the mixture. This mixture was stirred 60 °C for more than 2 h under N2 atmosphere. Figure 9 shows the structure of the core-shell microsphere in dry state. 

Ramtrez LP, Landfester K (2003) Magnetic polystyrene nanoparticles with a high magnetite content obtained by miniemulsion processes. Macromol Chem Phys 204 22-31 Landfester K, Ramirez LP (2003) Encapsulated magnetite particles for biomedical application. J Phys Condens Matter 15 S1345-S1361... 

Using miniemulsion polymerization, Gu et al. reported the synthesis of magnetic polystyrene latex and carboxylated magnetic polymer latex [173, 174]. In the lat-ter,carboxyl end groups were provided on the surface of the latex directly from the initiator 4,4-azobis (4-cyanopentanoic acid) (ACPA). The average size of the final magnetic particle was 250 nm. 

Figure 46 (a) Micrograph of polystyrene-based magnetic monodisperse particles the particle diameter is 2.8 imi. (b) The particles are subjected to an external magnetic field. (From Ref. 86.)... 

Recently, membranes with SP nanoparticles have been introduced which operate on a slightly different principle, as illustrated in Fig. 13.7. The membranes contain an ordered array of stimuli-responsive core-shell type magnetic polystyrene latex particles. The particles change their size in response to external stimuli, acting as on-off switches or permeability valves , regulating the permeation through membrane channels. 

FIGURE 6.5 Normalized I q) curve for a stable sample of a superparamagnetic polystyrene particle suspension. The experimental data are shown as points (O). The continuous curve (-) was calculated according to Mie s theory for polystyrene particles of the same size without any magnetic content. The dashed line (—) was calculated according to the RGD theory. 

The kinetics of the reaction of solid sodium iodide with 1-bromooctane were studied with a 95 % RS graft of polyethylene oxide) 6-mer methyl ether on 3 % CL polystyrene as catalyst (51)176). The rates were approximately first order in 1-bromooctane and independent of the amount of excess sodium iodide. The rates varied with the amount of the solid catalyst used, but there was not enough data to establish the exact functional dependence. All experiments employed powdered sodium iodide, magnetic stirring, and 75-150 pm catalyst beads. Thus the variables stirring speed and particle size, which normally are affected by mass transfer and intraparticle diffusion, were not studied. Yanagida 177) favors a mechanism of transfer of the sodium iodide by dissolution in the solvent (benzene) and diffusion to the catalyst particle... 

Fig. 37 Linear chain formation of DNA-coated paramagnetic polystyrene colloids with the different self-protection schemes displayed in Fig. 33. By using an external magnetic field, DNA-functionalized particles were brought together into linear chains, after which the temperature was lowered below the association temperature for beads, and the field turned off. (a) Representative microscopy picture of the resulting chain structures immediately after switching off the magnetic field, (b-d) Chains after 1 h at the specified temperature for particles functionalized with sticky end sequences able to form both loops and hairpins (b, c) or only loops (d). The degree of aggregation of chains in (d) is intermediate between the unprotected, branched chains in (b) and the perfectly linear, protected chains in (c). Adapted with permission from [157]...

Monodispersed polystyrene sols are used as calibration standards for electron microscopes, light scattering photometers, Coulter counters, particle sieves, etc. Monodispersed silica is used for antireflection lens coatings. Monodispersity (even at a modest level) can usefully be exploited in photographic film, magnetic devices, pharmaceutical preparations and catalysis. 

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