Dynamic Polypyrrole Core–Shell Chemomechanical Actuators

Conducting polymer fabricated oil-in-water (o/w) colloidal particles were developed via a single step of in situ interfacial polymerization of an emulsion phase, exhibiting a unique core–shell structure, where the shell was governed by a thin layer of a polypyrrole (pPy) film at the o/w interface. These core–shell particles afford dynamic actuating shapes and configurations when the pPy at the interface is chemically oxidized into the charged state or, alternatively, it is reduced into the noncharged state. Mechanisms of the particles' volumetric expansion rely on the repulsive interaction resulting from positively charged pPy as well as the insertion of reduced negatively charged oxidant species. Notably, these particles demonstrated the ability to expand up to 400% of their initial dimensions while retaining their structures and can shrink back to their original size. Electrochemical actuation tests also display similar structural changes of pPy particles as those obtained using chemical actuation. Measuring the size of the triggered expansion of pPy particles inside the different poly(ethylene glycol) (PEG) gels allows for the evaluation of the forces generated by the expansion of the particle interfaces. Organic dyes compatible with the core–shell actuating particles could be trapped within the interior of the core–shell structure, demonstrating the prospects for including different functionalities within this material system.