Deformable hollow hybrid silica/siloxane colloids by emulsion templating.

A procedure to obtain hollow colloidal particles has been developed using an emulsion templating technique. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysilane monomer and incorporated in a solid shell using tetraethoxysilane. Hollow shells were obtained by exchange of the core. The formation of the oil droplets was investigated using static light scattering and 29Si solution NMR, and the hollow shells were characterized by electron microscopy and static light scattering. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis and 29Si solid state NMR, revealing that the shells consist of a hybrid cross-linked network of silica and siloxane units. Confocal microscopy was used to show that the shells are permeable to small dye molecules. The thickness of the coating can be easily varied from a few nanometers upward. Depending on the ratio of shell thickness to particle radius, three types of hollow shells can be distinguished depending on the way in which they buckle upon drying. We designate them as microspheres, microcapsules, and microballoons. As a result of their monodispersity, these particles can be used for making 3D-ordered materials.