Description
Two Michigan State University chemists showed that when pressure is applied to an ionic liquid, it releases electricity proportional to the amount of pressure applied, presenting the first observation of the piezoelectric effect in liquids for the first time. In their article published in The Journal of Physical Chemistry Letters, Md. Iqbal Hossain and GJ Blanchard state that the ionic liquids at room temperature, 1-butyl-3-methyl imidazolium bis(trifluoromethyl-sulfonyl)imide (BMIM+TFSI–) and 1 -Hexyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide (HMIM+TFSI–) produced voltage after force application when confined within a cell, of less magnitude than that observed in quartz. "This is the first report of our knowledge on the direct piezoelectric effect in a pure liquid."
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The piezoelectric effect is the phenomenon by which certain materials generate electricity when stretched. On the contrary, when electricity is supplied, the material undergoes a change in shape.
The scientific phenomenon can be better understood with this working example.
In the gas igniter we use to light gas stoves, there is a small piezoelectric crystal, usually quartz or ceramic, sandwiched between two metal plates. When the igniter button is pressed, a small spring-loaded hammer strikes the glass, applying a mechanical force that deforms the structure.
This deformation causes the crystal to generate a voltage difference between the two metal plates which results in a high voltage spark being discharged through a spark gap to ignite the gas.
Therefore, the piezoelectric effect is used here to convert mechanical energy into electrical energy in the form of a spark.
The piezoelectric effect is mainly noticeable in solids due to the presence of a crystalline structure, with atoms or molecules arranged in a uniform pattern.
Until now it was believed, according to the generally accepted theory, that when a crystal is subjected to stress or mechanical pressure, the structure of the lattice deforms causing a change in the positions of the charged particles, thus developing a strain.
Because liquids and vapors do not have a well-defined and ordered crystalline structure, they do not exhibit the piezoelectric effect.
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Now, with the observation of the piezoelectric effect in liquid, the theory behind the phenomenon is being called into question, demanding a better understanding.
Furthermore, experts believe that liquid piezoelectric materials, especially those produced with ionic liquids, could be useful because they are more environmentally friendly than solid materials. They also point out that liquid piezoelectric materials may allow for greater variation in the shape of devices, opening up new design possibilities.
