The piezoelectric effect due to shear in oriented films of DNA is strongly dependent on the relative humidity at which the films are equilibrated. Below about 60% relative humidity, the sign of the piezoelectric modulus is negative and its magnitude passes through a maximum with increasing temperature. This type of polarization appears to be due to the stress‐induced orientation of dipoles in sugar‐phosphate main chain. Above 75% relative humidity, water molecules are adsorbed by the bases and stabilize the ordered structure of double strand helices. In this crystalline state, the sign of the piezoelectric modulus is positive and its magnitude decreases markedly at about−75°C. This type of polarization appears to be due to the stress‐induced orientation of dipoles in bases attached to the main chain. From comparisons between piezoelectric, elastic, and dielectric measurements, it is concluded that the piezoelectric relaxation observed at−75°C and 75% relative humidity is mainly due to the dielectric relaxation of the bases in the double helix.
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Ando et al. (1976) studied this question.
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