Electrostriction of dry films of purple membranes and their piezoelectric effect

Abstract

In this work, we present acousto-electrical measurements performed on dry films of purple membranes (PM) produced in bacteria Halobacterium salinarium. Electrical-to-mechanical coupling in PMs manifests itself as direct and inverse piezoelectric effects. Measurements performed on the samples with different degrees of PM orientation and at various values of the externally applied cross-membrane electric field indicate that piezoelectric phenomena in PMs arise from the electric asymmetry of the membranes, i.e., they originate from electrostriction. Experiments with samples made of oriented PMs shows the value of the intrinsic cross-membrane electric field 10 8 V/m.. Considering piezoelectric properties of PM films revealed by the experiments presented in this study, we can conclude that the films of oriented PM's can (at least, theoretically) be used as electric-to-accoustic (and vice-versa) converter with variable piezoelectric constant. This constant depends on the external DC field, which can be considered as the control parameter. Due to the fact that external illumination also changes cross-membrane field in PM (BR transfers the protons from the internal to the external side of the membrane), the control factor can also be the light.