Polypyrrole nanorods coated on cellulose nanofibers by pickering emulsion as conductive medium for multimodal gel-based sensor

Herein, a new interfacial polymerization of pyrrole (Py) by the oil in water Pickering emulsion was developed to overcome the undesirable polymerization rate and uneven deposition of the polypyrrole (PPy). In this Pickering emulsion, the pyrrole in the oil phase (cyclohexane) was slowly diffused into the water phase and polymerized on the surface of cellulose nanofibers (CNFs), achieving the PPy nanorods (about 100 nm in length, 20 nm in diameter) coated on the CNFs efficiently and uniformly. The PPy@CNF composites were well dispersed in a suspension. Furthermore, the resulting suspension could be applied in the design of the conductive and sensing hydrogel, and the PPy@CNF-PVA-PA hydrogel was assembled by the PPy@CNFs, polyvinyl alcohol (PVA) and phytic acid (PA) with the high conductivity (8.0 S/m), appropriate modulus and decent mechanical properties (460%, 0.42 MPa). The motions of the human mouth, and bending of fingers, wrists, and elbows can be readily monitored and detected by the hydrogel-based sensor. Meanwhile, the detected signal was stable, repeatable and positive correlation to the moving amplitudes. Therefore, the Pickering emulsion as a polymerization strategy blazed a trail in the preparation of the conductive composites, and the resulting hydrogel possessed tremendous potential in the field of touch skins, soft robotics, and flexible sensing devices.Graphical abstract