Mechanistic insights of evaporation-induced actuation in supramolecular crystals

Piotrowska, Roxana and Hesketh, Travis and Wang, Haozhen and Martin, Alan R. G. and Bowering, Deborah and Zhang, Chunqiu and Hu, Chunhua T. and McPhee, Scott A. and Wang, Tong and Park, Yaewon and Singla, Pulkit and McGlone, Thomas and Florence, Alastair and Tuttle, Tell and Ulijn, Rein V. and Chen, Xi (2020) Mechanistic insights of evaporation-induced actuation in supramolecular crystals. Nature Materials, n/a. n/a. ISSN 1476-1122

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    Abstract

    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.