Polyelectrolyte Brush Amplified Electroactuation of
Microcantilevers
Feng Zhou1, P. Maarten Biesheuvel1*,
Eun-Young Choi1 Wenmiao Shu1, Rosa
Poetes2, Ullrich Steiner2 and Wilhelm T S
Huck1*
1 Melville Laboratory for Polymer Synthesis, University of
Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
2 Department of Physics, Cavendish Laboratory, J J Thomson
Avenue, Cambridge, CB3 0HE, UK
We demonstrate how polyelectrolyte brushes can be used in the
electroactuation of cantilevers. By applying an alternating
positive and negative bias to a polyelectrolyte brush-covered
cantilever, significant surface stresses are generated, which are
several orders of magnitude larger compared to those obtained in
DNA hybridization. Changing the sign of the applied bias did not
reverse the deflection of the cantilever, but led to expansive
stresses at the brush-covered side of the cantilever in both
cases. We developed a theory based on a simplified
polyelectrolyte brush model to describe the state of the brushes
under positive and negative bias, and coupled this model to
Stoney's equation for cantilever bending. This theory
confirms that a bias in either direction should lead to expansive
stresses, with stresses at negative potential which are
significantly larger than for a positive bias. Our work opens new
possibilities for studying the behavior of polymer brushes under
electrical bias. In future work, we will explore the dynamics of
the system in more detail, since preliminary results indicate
that the cantilever actuation shows a complex time dependent
response. The electroactuation demonstrated here has potential
applications in microfluidic devices, where the ability to
actuate without changing the chemical environment is strongly
preferred.
References
F. Zhou, P. M. Biesheuvel, E.-Y. Choi, W. Shu, R. Poetes, U.
Steiner, W. T. S. Huck, Nano Letters, 2008, 8, 725
