An invisible bend sensor based on porous crosslinked polyelectrolyte film

This paper reports the fabrication and electromechanical characterization of a thin porous polyelectrolyte film and its application in an invisible bending transducer. The porous film consists of 10 bilayers of polycation and polyanion that are adsorbed using electrostatic self-assembly (ESA). Such porous film can be thermally crosslinked. The size of the pores on top surface is adjustable and can be covered up by a type of Na+-montmorillonite nanosheet whose size is comparable to those of the pores. As a result, the sealed top surface can be coated by metal for an electrode. After such polymeric film is integrated into a sandwich structure that was designed for a bend sensor, it can perform as an ultrathin piece of elastomer. It is found that the bending of the substrate resulted in the increasing of the current. It is hypothesized that the tunneling current through the thin polymeric film changes when the film is compressed by bending. Finite element simulation corroborates the existence of strain concentration especially near two ends of the polymer film and the shoulder of the bottom electrode.