Core-shell and core-shell-shell nanospheres with different amphiphilicities were synthesized by sequential condensation of trimethoxymethylsilane (T), diethoxydimethylsilane (D), and the functional monomer (chloromethylphenyl)trimethoxysilane (ClBz-T) and mixtures thereof. The condensation was performed in aqueous dispersion in the presence of surfactant. Saturation of reactive surface SiOH groups with monofunctional trimethylsilane monomers prevents interparticle condensation and leads to nanoparticles, which are redispersable in organic solvents. The diameters of the particles range between 20 and 40 nm, depending on the composition. The thickness of the outer, nonfunctionalized shell is determined by asymmetrical flow field-flow fractionation (AF-FFF) and dynamic light scattering (DLS) of the core and core-shell particles, respectively. It varies between 1.5 and 3 nm and is proportional to the volume of added monomer. Incorporating (chloromethylphenyl)siloxane groups in the core and performing a subsequent quaternization reaction of dimethylaminoethanol yield amphiphilic nanospheres with an ionic, hydrophilic core and a hydrophobic outer shell. The amount of ionic moieties is found to be proportional to the amount of functional (chloromethylphenyl)siloxane groups incorporated in the spheres. Additionally, multiple shell topologies were successfully prepared, i.e., particles with a poly(dimethylsiloxane) (PDMS) core, an ionic inner and a hydrophobic outer shell. If linear PDMS chains forming the core are prevented to chemically bind to the inner shell, they may be removed by ultrafiltration, resulting in the formation of hollow spheres.

The loading of amphiphilic poly(organosiloxane) nanoparticles with hydrophilic dyes in organic solvents depends inter alia on the construction of the nanoparticles (core-shell, hollow spheres), on the amphiphilicity, is adjustable by synthesis, and on the method of the phase transfer. For more information see the Communication by M. Maskos et al. on the following pages.

The advantages of asymmetrical flow field-flow fractionation (AF-FFF) for the characterization of aqueous dispersions of spherical polyorganosiloxane nanoparticles are discussed. With AF-FFF it was possible to obtain information about the synthesis, which is based on the hydrolysis and condensation of alkylalkoxysilanes in aqueous dispersion, and the average size of the spherical nanoparticles in the complex mixture in the presence of excess surfactant. The results are compared to measurements performed with dynamic light scattering (DLS). The size of the nanoparticles increases as a function of the amount of added monomer. Particles with radii between 2 and 50 nm are observed. If only the cross-linking monomer methyltrimethoxysilane (T) or a fixed monomer mixture of T and the chain-forming monomer diethoxydimethylsilane (D) is used, the increase in the radius shows a cube dependence on the volume of added monomer as expected. With AF-FFF it is also possible to obtain information on the role of the surfactant, which is needed to stabilize the particles. For spherical nanoparticles that are composed only of the trifunctional T or of a monomer mixture of T and D, it was found that the amount of surfactant needed to stabilize the growing particles is proportional to their surface. In the case of a more complex spherical core−shell architecture it was possible by AF-FFF analysis to obtain information about a secondary nucleation which may take place during the synthesis.

Amphiphilic poly(organosiloxane) nanospheres with different core-shell architectures are employed as passive nanoreactors for the synthesis of noble metal colloids. The amphiphilic poly-(organosiloxane) nanospheres, which have diameters between 15 and 40 nm, possess a hydrophilic interior and a hydrophobic shell. Dispersed in organic solvents such as toluene, it has been achieved to transfer hydrophilic noble metal salts through the solvent into the nanospheres by either liquid-liquid or solidliquid phase transfer. Subsequently, reduction of the noble metal salt with lithium triethylborohydride led to the formation of 2-5 nm sized noble metal colloids. If the network density of the shell of the poly-(organosiloxane) nanospheres is small enough, the colloids are topologically trapped inside the nanospheres and stabilized against aggregation. By employing hydrogen tetrachloroaurate(III), silver nitrate, or palladium(II) chloride, it was possible to synthesize topologically trapped gold, silver, or palladium colloids, respectively. The number, the size, and the stability of the colloids depend mainly on (i) the kind of phase transfer chosen, (ii) the amount of hydrophilic groups in the poly(organosiloxane) nanospheres, and (iii) the architecture of the poly(organosiloxane) nanospheres.

Bis zu 50 % Farbstoff bezogen auf das Eigengewicht nehmen Poly(organosiloxan)‐Nanopartikel mit quartären Ammonium‐Gruppen (Glas 1–3 mit hydrophilem Thymolblau als Modellsubstanz) im Unterschied zu ammoniumfreien Partikeln (Glas 4, 5) auf. Einfluss auf die Beladung haben unter anderem der Aufbau der Nanopartikel (Kern‐Schale, Hohlkugel), die durch die Synthese einstellbare Amphiphilie und die Art des Phasentransfers.