  Because of the flexoelectric effect, dielectric materials usually polarize in
response to a strain gradient. Soft materials are good candidates for
developing large strain gradient because of their good deformability. However,
they always suffer from lower flexoelectric coefficients compared to ceramics.
In this work, a flexoelectric-like effect is introduced to enhance the
effective flexoelectricity of a polydimethylsiloxane (PDMS) bar. The
flexoelectric-like effect is realized by depositing a layer of net charges on
the middle plane of the bar to form an electret. Experiments show that the
enhancement of the flexoelectricity depends on the density of inserted net
charges. It is found that a charged layer with surface potential of -5723V
results in 100 times increase of the material's flexoelectric coefficient. We
also show that the enhancement is proportional to the thickness of electrets.
This work provides a new way of enhancing flexoelectricity in soft materials
and further prompt the application of soft materials in electromechanical
transducers.
