Concentration core-shell particles

The analysis [47,49] of the scattering intensities reveals a well-defined concentric core-shell particle. The data taken near the match point (filled circles in Fig. 18b) show furthermore that there is a finite contribution to the SAXS-inten-sity at q=0 even near vanishing contrast. This points directly to a polydispersity of the average contrast, mainly caused by the variation of the thickness of the shell [47]. Another important point of this analysis is the interface between the core and the shell. Here the interfacial region between the two immiscible polymers was found to be very small (<4 nm [49]). 

In this way, Lu and coworkers [99] have prepared core-shell particles selective to 2,4-D, via RAFT controlled/living polymerization, to allow growth of uniform MIP shells with adjustable thicknesses (Fig. 13). Moreover, a competitive assay was accomplished between 2,4-D and the structurally related fluorophore 7-car-boxy-4-methylcoumarin (CMMC). A typical competitive curve is obtained in buffered solution. The useful concentration range for the detection of 2,4-D ranged from 50 nM to 20 pM. The detection limit was around 10 nM, making possible its application to real samples. 

On the other hand, when low concentrations of metal are used to cap the semiconductor core we can expect the outer layer to be discontinuous. Such a configuration of core shell particles (i.e. small metal islands deposited on the Ti02 core) provides a favorable geometry for facilitating the interfacial charge transfer under UV irradiation. It should be noted that, a new band appears at 390 nm in the case of Ti02/Au nanoparticles as the transient absorption corresponding to (SCN)2 ... 

As for the linear properties, numerous approaches have been proposed to predict and explain the nonlinear optical response of nanocomposite materials beyond the hypothesis leading to the simple model presented above ( 3.2.2). Especially, Eq. (27) does not hold as soon as metal concentration is large and, a fortiori, reaches the percolation threshold. Several EMT or topological methods have then been developed to account for such regimes and for different types of material morphology, using different calculation methods [38, 81, 83, 88, 96-116]. Let us mention works devoted to ellipsoidal [99, 100, 109] or cylindrical [97] inclusions, effect of a shape distribution [110, 115], core-shell particles [114, 116], layered composites [103], nonlinear inclusions in a nonlinear host medium [88], linear inclusions in a nonlinear host medium [108], percolated media and fractals [101, 104-106, 108]. Attempts to simulate in a nonlinear EMT the influence of temperature have also been reported [107, 113]. 

Equation(19) demonstrates that Rg of a composite particle diverges at the match point and that may become negative as well. This is shown in Fig. 5 for concentric monodisperse core-shell particles the radial electron density of which is given by Fig. 1 whereas the scattering function has already been discussed in conjunction with Fig. 2. Polydispersity of contrast tends to smear out this feature but it should be kept in mind that may change markedly when conducting measurements in the immediate vicinity of the match point. 

Equqtion (51.15) provides the extinction cross section for spherical particles in a dielectric medium. When the particles are coated by a surface layer, the optical properties of both the core and shell materials must be considered. The extinction cross section of a concentric core-shell sphere is given by [144],... 

Figure 4. UVA S/NIR spectrum of (a) imcoated, ZnS-coated, or PbS-coated 0.827 pm PS-CO2 microspheres in EtOH and PbS fihn on glass showing 80 nm red shift and (b) PbS/0.827 pm PS-COa in EK)H at higher concentrations. Oscillations seen in the ZnS spectrum, used to calculate particle size, were not visible for the PbS core-shell particles.

The active micro-reactors described above cannot be recycled because the SiH moieties cannot be renewed. Recyelable micro-networks may be realized in the form of passive miero-reactors which do not actively take part in the reaction but merely provide the confined reaction space. For this purpose hollow micro-networks are synthesized first, a micro-emulsion of linear poly(dimethyl-siloxane) (PDMS) of low molar mass (M = 2000-3000 g/mol) is prepared and the endgroups are deactivated by reaction with methoxytrimethylsilane. Subsequent addition of trimethoxymethyl-silane leads to core-shell particles with the core formed by linear PDMS surrounded by a crosslinked network shell. Due to the extremely small mesh size of the outer network shell the PDMS ehains become topologically trapped and do not diffuse out of the micro-network over periods of several months (Fig. 3). However, if the mesh size of the outer shell is increased by condensation of trimethoxymethylsilane and dimethoxydimethylsilane the linear PDMS chains readily diffuse out of the network core and are removed by ultrafiltration. The remaining empty or hollow micro-network collapses upon drying (Fig. 4). So far, shape-persistent, hollow particles are prepared of approximately 20 nm radius, which may be viewed as structures similar to crosslinked vesicles. At this stage the reactants cannot be concentrated within the micro-network in respect to the continuous phase. 

A series of SBR copolymers were prepared by emulsion polymerisation and an SAN copolymer was polymerised by a semicontinuous process in the presence of SBR to form a core/shell morphology. The effects of initiator concentration, monomer feeding rate, core/shell ratio, and gel fraction of the core on the core/shell particles morphology were studied. Morphology and Tg were characterised by TEM, DSC, and dynamic mechanical spectroscopy. 28 refs. 

The analysis of the scattering curves from the TSL samples leads to the conclusion that the particles have a concentric core-shell structure, in which a core of the first-stage polymer is enclosed in a shell of the... 

For DDMC of core-shell particles, when a low concentration of [E] and [S], the kinetic kl[E][S] may be small, because a Coulomb force between the phosphoric acid from nucleic acids and the diethyl-amino - ethyl (DEAE) group of DEAE-dextran should not be large enough to compare with hydrogen bond in its PIC structure and the hydrophobic force of the graft poly (MMA) for its conformation. That is why Km is much larger than [S], As Km [S ], we have... 

The nanoscale coating of colloid particles with materials of different compositions has been an active area of research in nanoscience and nanotechnology [2]. Deposition of metal nanoparticles on different colloid particles to form core-shell particles has been one of the most effective tools for achieving such composite nanostructures [172]. In particular, a number of studies on such composite structures were concentrated on the fabrication of metal coated latex particles, because of their potential applications in the fields of surface-enhanced I man scattering (SERS), catalysis, biochemistry, and so forth [173]. Conventionally, silver shells on polymer latex were prepared via wet-chemistry methods, which involve the activation of a latex surface by seeds of a different metal, followed by the deposition of the desired metal [174], or the modification of the latex with groups capable of interacting with the metal precursor ions on the latex surface via complex or ion pairs, and subsequent reduction [175]. 

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