Force and stroke of a hydrogel actuator

Hydrogels that undergo a volume phase transition in response to an
external stimulus are of great interest because of their possible use as
actuator materials. The performance of an actuator material is normally
characterized by its force–stroke curve, but little is known about the
force–stroke behavior of hydrogels. We use the theory of the ideal
elastomeric gel to predict the force–stroke curves of a
temperature-sensitive hydrogel and introduce an experimental method for
measuring the curve. The technique is applied to PNIPAm hydrogels with
low cross-link densities. The maximum force generated by the hydrogel
increases with increasing cross-link density, while the maximum stroke
decreases. The force–stroke curves predicted by the theory of the ideal
elastomeric gel are in very good agreement with the experimental curves.

This paper has appeared in Soft Matter and can be downloaded from:

http://www.seas.harvard.edu/suo/papers/311.pdf