Transient Grating Experiments on Inorganic–elastomer Nanocomposites

We studied the photo-elastic and photo-thermal response of two new nanocomposites base on a polyurea elastomer mixed with inorganic nanotubes (MoS2) or nanowires (Mo6S2I8). The investigation has been performed using time-resolved laser spectroscopy, transient grating technique (TG), based on short laser pulses. This spectroscopic tool enables the measurement of the thermoelastic response of the nanocomposites covering a very large time window, from nanoseconds to milliseconds, revealing the different dynamic phenomena present in these materials. On the fast timescale (from 1 to 100 ns) the TG signal shows the propagation of a high frequency acoustic wave enabling the measure of its sound velocity and damping time. In the slow time window (from 5 to 100 $\mu$s) the TG signal presents a slow decay due to the thermal diffusion process. As expected, these features are common for both pure polymeric and nanocomposite samples. Surprisingly, the presence of nanotubes or nanowires in the polymeric matrix produces on the intermediate time scale a new dynamic phenomenon in the experimental data, whose origin is not clear.