Using Ultrasound Wave Propagation to Estimate the Dispersion of Nanostructures in Polymers with Complex Molecular Architectures

One of the key points for the successful development of nanocomposites is to obtain a good dispersion of the nanofillers in the polymer matrix. However, because of complex polymer-polymer and polymer-nanostructure interactions, the estimation of the dispersion is far from trivial. Dynamic rheological functions are mostly used to estimate the quality of dispersion. However, these rheological functions are sensitive to complex molecular architectures such as branching; thus, the accuracy of these rheological functions is limited for nanocomposites obtained using polymer matrices with these molecular architectures. Therefore, an estimation of the dispersion using other approaches needs to be explored. In this work, carbon nanotubes (CNTs) are firstly dispersed in a polyamide matrix by a low-frequency ultrasound-assisted extrusion process (kHz range). Then, high-frequency ultrasound wave propagation (MHz range) is used to estimate the dispersion of CNTs in polyamide matrices with different branching architectures. The quality of dispersion observed through the ultrasonic attenuation coefficient of the material matches with optical microscopy studies, in contrast with results obtained using dynamic rheological functions. Dynamic mechanical deformation induced by high-frequency ultrasound seems to be less sensitive to branching architectures, thus giving a better estimation of the quality of dispersion.