The Piezoelectric Effect in Liquids

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Context:

For the first time, scientists have reported evidence of the piezoelectric effect in liquids.

Relevance:

GS III: Science and Technology

Dimensions of the Article:

The effect has been known for 143 years and in this time has been observed only in solids.
The new finding challenges the theory that describes this effect as well as opens the door to previously unanticipated applications in electronic and mechanical systems.
The effect was found in pure 1-butyl-3-methyl imidazolium bis(trifluoromethyl-sulfonyl)imide and 1-hexyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide — both ionic liquids (liquids which are made of ions instead of molecules) at room temperature.

In the piezoelectric effect, a body develops an electric current when it is squeezed.
Quartz is the most famous piezoelectric crystal; it is used in analog wristwatches and clocks. Such crystals are also used in other instruments where converting mechanical stress to a current is useful.
Quartz is silicon dioxide (SiO2). The quartz crystal consists of silicon and oxygen atoms at the four vertices of a three-sided pyramid; each oxygen atom is shared by two pyramids.
These pyramids repeat themselves to form the crystal.
The effective charge of each pyramid is located slightly away from the centre.
When a mechanical stress is applied, that is when the crystal is squeezed, the position of the charge is pushed further from the centre, giving rise to a small voltage. This is the source of the effect.

Lack of Organized Structure: The piezoelectric effect is expected to occur in solids because they have an organized structure, which allows them to maintain a stable shape under pressure. Liquids, on the other hand, do not have such a structure and take the shape of the container they are in.
Non-Compressible: Hooke’s law, which explains the linear relationship between force and compression, is not clear when the body being squeezed is not very compressible.
Inconsistency with Current Model: The observation of the piezoelectric effect in ionic liquids appears to be inconsistent with the current model, which requires “persistent” order within the material.
Existence of Organization: The discovery of the piezoelectric effect in ionic liquids suggests that there is some manner of organization within these liquids that is not seen in “normal” liquids.
Molecular-Level Response: Normal and ionic liquids of the kind tested in the study respond very differently at the molecular level when an electric charge is imposed on them.

More Accessible Applications: According to the paper, the discovery opens the door to applications that were previously not accessible with solid-state materials. This could lead to the development of new technologies that were not possible before.
Recyclability and Environmental Benefits: Room-temperature ionic liquids are more readily recyclable and pose fewer environmental issues than many currently used piezoelectric materials.
Dynamic Focusing Abilities: The inverse piezoelectric effect displayed by the liquids could be used to control how they bend light passing through them by passing different currents through them. This could lead to the development of vials of these liquids that act as lenses with dynamic focusing abilities.
Better Understanding of Behaviour: Having a theory to explain the liquids’ behavior could reveal why they behave the way they do, which could lead to the development of newer and better applications.

-Source: The Hindu