# The Direct Piezoelectric Effect in Deep Eutectic Solvents

## TL;DR

This paper shows that deep eutectic solvents can exhibit a piezoelectric effect, similar to ionic liquids, opening new possibilities for material design.

## Contribution

The first observation of the direct piezoelectric effect in deep eutectic solvents, demonstrating its generality beyond ionic liquids.

## Key findings

- Four deep eutectic solvents showed a linear piezoelectric response when force was applied.
- The piezoelectric coefficient (d33) in these solvents is comparable to that in room-temperature ionic liquids.
- The phenomenon suggests that the piezoelectric response can be tuned by selecting appropriate solvent constituents and ratios.

## Abstract

We report the direct piezoelectric response of four deep
eutectic
solvents (DESs): choline chloride:ethylene glycol (ChCl:EG), choline
chloride:glycerol (ChCl:Gly), choline chloride:1,3-propanediol (ChCl:PD),
and choline chloride:urea (ChCl:urea). Measurement of current as a
function of applied force produces a linear relationship from which
the piezoelectric coefficient (d
33) was
determined. The piezoelectric effect has previously been observed
in room-temperature ionic liquids (RTILs), attributable to a pressure-induced
liquid-to-crystalline solid phase transition. The observation of this
phenomenon in DESs is unprecedented and underscores its generality.
The magnitude of d
33 in these DESs is
similar to that for RTILs, suggesting the potential to tune the piezoelectric
response through careful selection of the DES constituents and constituent
ratios.