EAGER: TORSIONAL PIEZOELECTRICITY IN CHIRAL SOLIDS

NON-TECHNICAL ABSTRACT

This project will investigate the twisting behavior of biological molecules. Many biological molecules are chiral—like our left and right hands, they exist in two mirror-image forms that are chemically identical but structurally distinct. DNA, with its helical shape is chiral.

Amino acids, and sugars, all have “right-handed” and “left-handed” versions; as do screws, Slinkys, and springs. In principle, objects with this kind of mirror asymmetry can produce a voltage when we twist them, or twist when we apply a voltage. The catch?

It works best when the chiral objects are very small, on the scale of molecules. This project will exploit the electric potential of common biological molecules to create cheap, abundant power sources and microscopic motors. Through publications, demonstrations, and interactive presentations, the team will share the exciting properties of chiral molecules with the scientific community, K-12 students, and the science-curious public.

TECHNICAL ABSTRACT

This project will explore how solids made of randomly-oriented chiral molecules act as torsional piezoelectrics, generating voltage in response to a twist and twisting in response to a voltage. The majority of biological molecules are chiral, allowing for a range of cheap, abundant materials to explore for power related applications . Because the symmetry breaking arises from the molecular chirality rather than crystallinity, even amorphous and polycrystalline solids made of chiral molecules can, in principle, exhibit torsional piezoelectricity.

Arguments based only on mirror symmetry indicate that non-zero components of the piezoelectric tensor exist and must switch sign for chiral enantiomers This two-year project will study both left- and right-handed enantiomers of at least three different molecules to establish a general relationship between chirality and torsional piezo-electricity. Amorphous and crystalline solids of chiral molecules will be fabricated via melting with fast and slow cooling, and sintering.

The direct piezoelectric effect will be measured by subjecting the solids to torsional stresses in a variety of geometries and measuring the resulting voltage. The inverse effect will be obtained by subjecting the solid to different voltage configurations and measuring the motion using optical methods. The intellectual merits of this project include the elucidation of novel piezoelectric symmetry breaking mechanisms that may result in functional materials as well as torsional piezoelectric mechanisms for biological energy transfer/mechano-sensing.

This work will also provide the community with new insights into the general theory of piezoelectricity in the context of chiral solids.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.