SM01.02.07 : Redox-Responsive Soft Actuators

4:30 PM–4:45 PM Apr 3, 2018

PCC West, 100 Level, Room 104 AB

Jonathan Barnes1 Angelique Greene1 Mary Danielson1 Kevin Liles1 Abby Delawder1

1, Washington University in St. Louis, St. Louis, Missouri, United States

The development of new actuatable materials that can change their size, shape, and mechanical properties in response to an external stimulus, or multiple stimuli, has gained considerable attention recently. Such functional materials can be applied towards making new functional sensors, self-healing materials, and soft robotics, to name a few examples. The use of redox-active polymers in stimuli-responsive materials is particularly attractive because they can be activated either chemically or electrochemically. My research group has recently developed a new unimolecular redox-responsive macromolecular platform consisting of up to ten 4,4′-bipyridinium (a.k.a. viologen) subunits that are tethered by water-soluble and flexible oligoethylene glycol spacers. Upon chemical reduction of the individual dicationic viologen subunits to the corresponding radical-cations (i.e., V2+ to V+), a decrease in electrostatic repulsion occurs, as well as non-covalent intramolecular recognition between the main-chain radical viologen subunits positioned along the polymer backbone; a combined process which results in the collapse of the redox-active polymer chain. Incorporation of these oligoviologens into a hydrogel network primarily made of polyethylene glycol, followed by chemical reduction, resulted in the reversible contraction of a series of hydrogels down to one-tenth of their original starting volumes, where the majority of contraction occurred during the first 25–45 minutes. My group is now exploring how this process can be controlled by other stimuli. In my presentation, I will discuss the activation of our viologen-based soft actuators using a photoredox-based mechanism, and I will highlight how these materials are capable of lifting weights over defined distances, and therefore performing work as an artificial molecular muscle.