Polymer blends in nanoparticles have been studied by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The TEM studies show that blend particles formed from two immiscible polymers by the miniemulsion process exhibit biphasic morphologies. The fact that no core-shell type but Janus-like structures were found indicates that the surface free energies between both polymers and the solution-water interface (including the surfactant molecules) are similar; therefore, the blend morphology and composition of the individual phases are mainly determined by the interaction between the two polymer components. Both the TEM studies and the PL experiments provide strong evidence that phase separation in these particles strictly follows the Flory-Huggins theory. This highlights the applicability of the nanoparticle approach to fabricate blend systems with well-controllable properties and to study structure-property relationships under well-defined conditions.

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Janus nanoparticles with a poly(L-lactide) face and a polystyrene-based face functionalized with amine or carboxylic acid groups were synthesized via two different approaches. In the first approach, the poly(styrene-co-methacrylic acid) or poly-(styrene-co-2-aminoethyl methacrylate) copolymers were generated in situ in miniemulsion droplets before phase separation between the copolymers and the poly(L-lactide) occurred. In the second approach, the copolymers were prepared before the emulsification step. A solution containing the poly(L-lactide) and one of the copolymers was then emulsified, and the solvent was subsequently removed to induce a phase separation between the polymers, yielding a Janus morphology. The density of functional groups (amine or carboxylic acid) could be varied between 0 and 5 groups per nm 2 . Finally, we demonstrated that one face of the Janus nanoparticle could be selectively employed for a chemical reaction. Indeed, silver nanoparticles could be nucleated selectively on the poly(L-lactide) face.

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The function of an organic solar cell relies on making a contact surface between a donor and acceptor material. For an efficient conversion of solar energy, this heterojunction must be...