RESUMO
Inspiration for the design of new synthetic polymers can be found in the natural world, where materials often exhibit complex properties that change depending on external stimuli. A new synthetic electroplastic elastomer hydrogel (EPEH) that undergoes changes in mechanical properties in response to both chemical and electrochemical stimuli has been prepared based on these precedents. In addition to having the capability to switch between hard and soft states, the presence of both permanent covalent and dynamic copper-based cross links also allows this stimuli-responsive material to exhibit a striking shape memory capability. The density of temporary cross links and the mechanical properties are controlled by reversible switching between the +1 and +2 oxidation states.
RESUMO
The dawn of the 21st century has brought with it an increasing interest in emulating the adaptive finesse of natural systems by designing materials with on-demand, tunable properties. The creation of such responsive systems could be expected, based on historical precedent, to lead to completely new engineering design paradigms. Using a bioinspired approach of coupling multiple equilibria that operate on different length scales, a material whose bulk mechanical properties can be manipulated by electrical input has been developed. The new macroscale electroplastic elastomer hydrogels can be reversibly cycled through soft and hard states while maintaining a three-dimensional shape by sequential application of oxidative and reductive potentials. This input changes the cross-linking capacity of iron ions within the gel matrix, between a poorly coordinating +2 and a more strongly binding +3 oxidation state. Inclusion of carbon nanotubes in the hydrogel preparation increases conductivity and decreases transition time.
