Water-responsive materials undergo reversible shape changes upon varying humidity levels. These mechanically robust yet flexible structures can exert substantial forces and hold promise as efficient actuators for energy harvesting, adaptive materials and soft robotics. Here we demonstrate that energy transfer during evaporation-induced actuation of nanoporous tripeptide crystals results from the strengthening of water hydrogen bonding that drives the contraction of the pores. The seamless integration of mobile and structurally bound water inside these pores with a supramolecular network that contains readily deformable aromatic domains translates dehydration-induced mechanical stresses through the crystal lattice, suggesting a general mechanism of efficient water-responsive actuation. The observed strengthening of water bonding complements the accepted understanding of capillary-force-induced reversible contraction for this class of materials. These minimalistic peptide crystals are much simpler in composition compared to natural water-responsive materials, and the insights provided here can be applied more generally for the design of high-energy molecular actuators.
Bibliographical noteFunding Information:
This work was supported in part by the Office of Naval Research (ONR; N00014-18-1-2492), the Air Force Office of Scientific Research (AFOSR; FA9550-19-1-0111), the National Science Foundation (NSF; CHE-1808143), the EPSRC-funded ARCHIE-WeSt High Performance Computer (www.archie-west.ac.uk) for computational resources via EPSRC grant no. EP/K000586/1 and the CUNY/Strathclyde partnership. We acknowledge that the powder X-ray diffraction and DVS experiments were carried out in the CMAC National Facility, housed within the University of Strathclyde’s Technology and Innovation Centre, and funded with a UKRPIF (UK Research Partnership Institute Fund) capital award, SFC ref. H13054, from the Higher Education Funding Council for England (HEFCE). C.T.H. acknowledges the support of the National Science Foundation (NSF) Chemistry Research Instrumentation and Facilities Program (CHE-0840277) and Materials Research Science and Engineering Center (MRSEC) Program (DMR-1420073).
© 2020, The Author(s), under exclusive licence to Springer Nature Limited.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering