title: Perpetually self-propelling chiral single crystals.
abstract: When heated, single crystals of enantiomerically pure D- and L-pyroglutamic acid (PGA) are capable of recurring self-actuation due to rapid release of latent strain during a structural phase transition, while the racemate is mechanically inactive. Contrary to other thermosalient materials, where the effect is accompanied by crystal explosion due to ejection of debris or splintering, the chiral PGA crystals respond to internal strain with unprecedented robustness and can be actuated repeatedly without deterioration. It is demonstrated that this superelasticity is attained due to the low-dimensional hydrogen-bonding network which effectively accrues internal strain to elicit propulsion solely by elastic deformation without disintegration. One of the two polymorphs (β) associated with the thermosalient phase transition undergoes biaxial negative thermal expansion (αa = -54.8(8) × 10(-6) K(-1), αc = -3.62(8) × 10(-6) K(-1)) and exceptionally large uniaxial thermal expansion (αb = 303(1) × 10(-6) K(-1)). This second example of a thermosalient solid with anomalous expansion indicates that the thermosalient effect can be expected for first-order phase transitions in soft crystals devoid of an extended 3D hydrogen-bonding network that undergo strongly anisotropic thermal expansion around the phase transition.
authors.affiliation: New York University Abu Dhabi , P.O. Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: Manas K
authors.initials: MK
authors.lastname: Panda
authors.forename: Tomče
authors.initials: T
authors.lastname: Runčevski
authors.forename: Ahmad
authors.initials: A
authors.lastname: Husain
authors.forename: Robert E
authors.initials: RE
authors.lastname: Dinnebier
authors.forename: Panče
authors.initials: P
authors.lastname: Naumov
mesh_terms: D004548:Elasticity; D006358:Hot Temperature; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D009038:Motion; D044367:Phase Transition; D011761:Pyrrolidonecarboxylic Acid / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D011761:Pyrrolidonecarboxylic Acid