Metallic muscles: enhanced strain and electrolyte-free actuation

PhD ceremony: Mr. E. Detsi, 14.30 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Metallic muscles: enhanced strain and electrolyte-free actuation

Promotor(s): prof. J.T.H.M. de Hosson, prof. P.R. Onck

Faculty: Mathematics and Natural Sciences

Recently, a new class of artificial muscles made of nanoporous metals has emerged. Metallic muscles, as they are called, operate at low voltages, i.e. ~1V compared to e.g. piezoceramics that require more than 100 V. However, metallic muscles suffer from some drawbacks caused by the liquid medium (electrolyte) that they need to work.

(1) The low electrical conductivity of the liquid restricts the speed of the muscle.

(2) Metallic muscles undergo corrosion due to chemical reactions that take place in the liquid when a voltage is applied.

(3) Wet environments are not suitable for practical applications.

Rather, a dry environment is preferable. In this thesis, we design nanoporous gold with a new morphology consisting of a two-microscopic length scale structure; and we exploit the deformation mode in this new structure to significantly improve the strain amplitude in metallic muscles, up to ~60 times higher than in nanoporous metals with the standard uniform microstructure. To tackle the problems mentioned above in (1), (2) and (3), we replace the liquid medium by a polymer. Metallic muscles used in combination with a polymer move above 1400 times faster than in a liquid electrolyte.

An interesting multifunctional artificial muscle results when this nanoporous metal/polymer composite is used in an electrolyte: when an electrical voltage is applied to this composite material, the nanoporous metal changes its size while in the meantime the polymer changes its color. The work presented in this thesis is expected to stimulate a further development of metallic muscles towards applications.