Polypyrrole containers grown on oil microdroplets: encapsulation of fluorescent dyes

Polypyrrole microcapsules were synthesized by the chemical deposition of the polymer onto mineral oil droplets adsorbed onto glass or quartz substrates. The droplets act as a kind of a template that directs the polymer growth into the form of three-dimensional containers. The polymer is deposited on both the surface of oil droplets and the glass or quartz substrate entrapping the oil content. The dissolution of chemical species in oil prior to polymer deposition permits the encapsulation of these species within the cavities of the containers. This phenomenon was demonstrated through the entrapment of the fluorescent dyes, pyrene and perylene, within the polymeric capsules. It was shown that the entrapped molecules can be released from the capsules by controlling the hydration of the polymer, which in turn changes the permeability of the oil content through the polypyrrole shells. The polymer growth and encapsulation phenomena were investigated with a range of complementary physicochemical techniques, including microscopic (AFM, SEM, and confocal microscopy) and spectroscopic (steady-state fluorescence and UV-vis absorption) methods. In particular, the use of optical methods was possible due to the deposition of the capsules on transparent substrates (glass, quartz). As a consequence, the optical information on the interior of the capsules was accessible, for example, dye concentration and local polarity.