Ultrasound attenuation in polystyrene latexes

The ECAH theory, named after the successive works of Epstein and Carhart and Allegra and Hawley, is a very powerful tool that allows the estimation of the particle size distribution in diluted dispersions from ultrasonic attenuation measurements. However, in the case of low-density contrast systems such as polymer latexes, discrepancies have been reported by various authors between the predicted and experimental data at the lower frequencies (below 20 MHz). To elucidate the reasons for such a mismatch, the role of the intrinsic attenuation of the polymer is investigated in this work. A new method for measuring the intrinsic attenuations using a commercial unit is developed and applied to polystyrene in the frequency range 1-120 MHz. A linear relationship between the sound attenuation and the frequency is obtained, which differs significantly from the previous data in the literature. With the use of these values for the intrinsic attenuation, it has been found that the predictions of the attenuation spectra in polystyrene latexes given by the ECAH model are in good agreement with the experimental data.