Nonlinearity parameters of polymers

Two types of acoustic nonlinearity parameters for solids are discussed. The results of measurements of these parameters for three polymers-PMMA, polystyrene, and polysulfone-are presented. A recently developed technique using piezoelectric transducers directly bonded to the specimens allows the measurements of fundamental and second harmonics generated in solids, and thereby the determination of a nonlinearity parameter β₃, which is the ratio of a linear combination of second- and third-order elastic coefficients to the second-order elastic coefficient. The second nonlinearity parameter, B/A, is determined from the temperature and pressure derivatives of the sound velocity. The results from the two techniques are shown to be consistent. Using these nonlinearity parameters, the authors discuss the interchain interactions in polymeric solids and the characterization of polymers