Sign reversal of piezoelectric polarization of hydrated native collagenous and cellulosic fibers by addition of ions

Complex piezoelectric constants of native collagenous and cellulosic fibers, which take highly oriented and ordered microfibrilar structures, have been measured at 10 Hz between −150 and 50°C. We have found that piezoelectric polarization of both hydrated fibers, which contain many ions, steeply decrease around −60°C and subsequently exhibit the sign reversal around −40°C. These temperatures are found to agree with that at which bound water between the microfibrils begin to get mobile. The steep decrease and sign reversal of the piezoelectric polarization may be explained by actions of ions that reside in piezoelectric and nonpiezoelectric regions of such ordered structures.