Assembly of latex particles by using emulsion droplets as templates .1. Microstructured hollow spheres

We describe an emulsion-based technique that allows the assembly of colloid particles into microstructured or multicomponent clusters (''supraparticles''). The particles are gathered, assembled, and fixed together in the restricted, colloid-size 2D or 3D space provided by emulsion droplets. The process is carried out by multiple modification of the colloid interactions within the particle/droplet system-''interaction-tailored colloid assembly''. In the first paper of the series we provide a general description of the method. Then we present the data on the assembly of negatively charged (sulfate) or positively charged (amidine) latexes into ordered hollow spherical supraparticles. The following steps are included in the assembly schemes: (1) modification of latex surface charge and properties, so the microspheres are able to adsorb on the droplet surfaces but without homocoagulation; (2) adsorption and structure formation around the emulsion drops (at this stage the interfacial mobility of the particles is of crucial importance); (3) sterical protection of the particle/droplet complexes against coagulation or flocculation; (4) ''binding'' of particles within the assembled microspheres by strong coagulant; (5) extraction of the supraparticles by dissolving the carrier droplets in the surrounding environment. To characterize the electrostatic interactions throughout the assembly stages, we used electrophoretic mobility measurements. The electrophoretic data are in good qualitative agreement with the interaction-tailored assembly scheme. Clues on the other interactions involved are provided by altering the assembly process and using different modifying agents.