Electrochemical actuation in a nanoporous silicon-polypyrrole hybrid material

Porous silicon provides a scaffold structure to study the confinement related effects of soft matter. We investigate the electro-sorption of electrolyte anions and the electrochemical behaviour of nanoporous silicon in acidic electrolytes. The silicon-electrolyte interface acts as a capacitor which allows the accumulation of electrolyte anions in a chemical double layer by an applied voltage, whose characteristics can be measured by cyclic voltammetry. The surface stresses that are caused to the monolithic porous silicon membrane by such an accumulation lead to a macroscopic strain which can be measured in-situ with a dilatometer.
Furthermore, we investigate the properties of a functional filling of the electrically conductive polymer polypyrrole (PPy) into nanoporus silicon. We successfully demonstrate the filling of PPy into pores of substantial depth by electro-polymerisation. In particular, PPy allows for actoric applications for the hybrid system. Polypyrrole swells when it is exposed to a voltage in an electrolyte, since ions from the electrolyte are inserted into the polymer structure and expelled subsequently. The confinement effect of the pores on the swelling can be studied with dilatometry measurements.