Study on the electromechanical properties of polyimide composites containing TiO ₂ nanotubes and carbon nanotubes

New polyimide composite membranes were prepared by physical incorporation of different amounts of TiO₂ nanotubes (TNTs) and carbon nanotubes (CNTs) into a poly(amic acid) solution, followed by film casting and thermal imidization. The poly(amic acid) was synthesized by polycondensation reaction of 4,4′-(1,3-phenylenedioxy)dianiline with 4,4′-oxydiphthalic anhydride, in N-methyl-2-pyrrolidone as solvent. TNTs having outer diameters of approximately 10–12 nm and length of several hundred of nanometers were obtained by hydrothermal method. Their surface was modified by treating with 3-aminopropyltriethoxysilane to enhance organic–inorganic compatibility and to avoid agglomeration. A study of microelectromechanical properties of these membranes was performed. The influence of filler content on nanometric displacements when an electric voltage is applied on the membrane surface was determined. Also, theoretical aspects on the combined effects thermal and electrostrictive actuation are presented. The longitudinal microactuation included only electrothermal effect. The microactuation including electrostrictive effect as well as electrothermal effect was remarkable to the small electric field intensity and to small temperature domain.