5. Conclusions
Surface modification of the BaTiO3 particles with aminosilane
led to a higher piezoelectric coefficient for solvent cast composite
films, attributed to a better polarization of BaTiO3. Different decay
kinetics of the piezoelectric coefficient with time after poling were
observed for both solvent cast and compression molded composites
made with pristine versus modified particles. In addition to
the polarization of the ceramic particles and of the polymer matrix,
other effects, such as the formation of electrets or space charges,
which may also be influenced by the poling conditions, are suspected
to contribute to the rapid decay of the piezoelectric
response of the composites after poling. Characteristic times span
from only few hours in the case of composites made with pristine
BaTiO3 to more than one week when modified powders were used.
It is thus recommended, when studying the electromechanical
response of polymer–ceramic composites, to take into account that
the time needed to achieve a stable d33value after poling may differ
depending on the properties of the polymer–ceramic interface and