High-energy shape memory polymer could someday help robots flex their muscles

When stretched or deformed, condition memory polymers return to their primary shapes soon after heat or light-weight is used. These elements clearly show good promise for gentle robotics, good biomedical products and deployable area structures, but until now they haven’t been ready to shop sufficient power.

Now, scientists reporting in ACS Central Science have designed a condition memory polymer that merchants almost six times far more power than former versions.

An synthetic muscle mass manufactured of a stretched condition memory polymer contracts on heating, bending a mannequin’s arm. Impression credit history: Adapted from ACS Central Science 2021, DOI: 10.1021/acscentsci.1c00829

Condition memory polymers alternate involving an primary, undeformed point out and a secondary, deformed point out. The deformed point out is designed by stretching the polymer and is held in put by molecular changes, this sort of as dynamic bonding networks or pressure-induced crystallization, that are reversed with heat or light-weight. The polymer then returns to its primary point out through the release of saved entropic power. But it’s been demanding for scientists to make these polymers accomplish power-intense tasks. Zhenan Bao and colleagues wanted to produce a new variety of condition memory polymer that stretches into a steady, remarkably elongated point out, allowing it to release large amounts of power when returning to its primary point out.

The scientists integrated four-,4’-methylene bisphenylurea models into a poly(propylene glycol) polymer backbone. In the polymer’s primary point out, polymer chains were tangled and disordered. Stretching brought on the chains to align and form hydrogen bonds involving urea teams, producing supermolecular structures that stabilized the remarkably elongated point out. Heating brought on the bonds to crack and the polymer to deal to its first, disordered point out.

In tests, the polymer could be stretched up to 5 times its primary duration and shop up to 17.9 J/g power –– almost six times far more power than former condition memory polymers. The workforce shown that the stretched materials could use this power to lift objects 5,000 times its individual excess weight on heating. They also manufactured an synthetic muscle mass by attaching the pre-stretched polymer to the upper and decrease arm of a wood mannequin. When heated, the materials contracted, resulting in the mannequin to bend its arm at the elbow. In addition to its record-substantial power density, the condition memory polymer is also cheap (uncooked elements price tag about $eleven for every lb) and straightforward to make, the scientists say.

Supply: acs.org