Actuator of double layer film composed of carbon nanotubes and polypyrroles

We fabricate double layer films composed of millimeter-long ‘super-growth’ carbon nanotube (SG-SWNT) and polypyrrole (PPy) by electropolymerization of pyrrole on the SG-SWNT film surface under various conditions. Electrical and mechanical properties as well as morphologies of the obtained double layer films are studied by a four-probe DC current method, stress–strain measurements and scanning electron microscope (SEM) measurements. The growth process of PPy on the SG-SWNT film during electropolymerization is also investigated in detail. SG-SWNT/PPy double layer films show higher electrical conductivities and breaking strengths compared to both SG-SWNT and PPy single layer films. The fracture surface morphologies of the double layer films revealed that very fine fibrous SG-SWNTs came out on the cleavage section of PPy particles. Such a interconnected structure between SG-SWNTs and PPy was supposed to allow a new electrical conductive pass and reinforce the strength of the composite materials. Actuation performances of the SG-SWNT/PPy double layer films were also demonstrated in an aqueous solution. One of the features of this actuator is reversion of displacement direction depending on scan rate range when a relative amount of PPy component is large. This reversion of displacement direction is supposed to be based mainly on volume changes of PPy governed by several factors including ion movement, while volume changes of both SG-SWNT and PPy layers should contribute the actuation behavior.