An artificial musculus made of a stretched signifier representation polymer contracts upon heating, bending a mannequin’s arm Adapted from ACS Central Science 2021, DOI: 10.1021/acscentsci.1c00829
A polymer that changes signifier erstwhile heated tin assistance objects 5000 times its ain weight, with imaginable applications for robotics.
Shape-memory polymers flip betwixt their mean state, wherever molecules are flexible and disordered, and their deformed state, wherever the molecules hindrance into chains aft being stretched. Once successful the stretched, deformed state, the polymer tin beryllium unstretched –resuming its ‘normal’ authorities – by applying vigor oregon light.
However, accepted shape-memory polymers bash not store important amounts of vigor portion being stretched – meaning they don’t merchandise overmuch vigor portion unstretching, which limits their usage successful tasks that impact lifting oregon moving objects.
Zhenan Bao astatine Stanford University and her colleagues person present produced a shape-memory polymer that does store and merchandise appreciable amounts of energy. Their polymer has a poly(propylene glycol) backbone to which they added 4-,4’-methylene bisphenylurea units.
When stretched, the polymer chains go physically aligned, and intra- and intermolecular bonds – called hydrogen bonds – signifier betwixt the chains. These assistance the worldly support its highly stretched form. Then, erstwhile heated to 70 °C, the hydrogen bonds interruption and the worldly tin revert to its archetypal unstretched form, releasing vigor from the bonds successful the process.
Those longer fibres let the polymer to beryllium stretched to 5 times its archetypal length, and to store up to 17.9 Joules of vigor per gram successful its stretched signifier – six times astir different signifier representation polymers. “It could beryllium utilized to assistance weight, oregon to assistance to assistance oregon supply further propulsion to idiosyncratic who possibly is having trouble walking,” says Bao.
To show its imaginable uses, the squad turned the worldly into an artificial musculus betwixt the precocious and little limb of a woody mannequin. When the mannequin’s elbow associated was stretched, the polymer stretched too. Then, by applying vigor to the polymer, it contracted again, causing the mannequin’s elbow associated to bend.
“The reliable characteristics, and precocious spot of the worldly connection a caller method for designing joints that are susceptible of lifting aggregate times the worldly weight,” says Jonathan Aitken astatine the University of Sheffield, UK. However, Aitken questions whether the temperatures the polymer needs to beryllium heated to marque it applicable to use.
Bao hopes to adjacent analyse the polymer’s properties to spot if determination is simply a molecular mechanics that tin automatically elongate and shrink erstwhile changing somesthesia naturally.
Journal reference: ACS Central Science, DOI: 10.1021/acscentsci.1c00829
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