Rheology: A sensitive technique to probe the nanofiller organization in polymer nanocomposites

Rheology was shown to be an efficient technique to probe the nanocomposite microstructure. Above the percolation threshold, the dispersed (nano)fillers form a 3D-network in the polymer matrix. The rheology allows to characterize the mechanical response of the filler network in a molten/fluid polymer matrix. Under oscillatory solicitation, in the linear viscoelastic regime, the signature at low frequency of the filler network is a constant plateau, which translates in the presence of an apparent yield stress on the viscosity curve (Figure 1). Fitting the viscosity curve with a Carreau-Yasuda low with a yield stress allows to determine the apparent yield stress. This yield stress was shown to be correlated to the dispersion state of the nanofiller and used as a descriptor of the nanocomposite microstructure at the nanoscale [1-2].It is now clear that the nanocomposite microstructure needs to be characterized at different scales. At the macroscale, SEM observations, for example, can be used to quantify the fraction of remaining agglomerates. Rheology can used to characterize the dispersion at a nanoscale. It is always interesting to couple complementary techniques to characterize the dispersion state, for example X-rays to characterize the intercalation distance between platelets in clay, TEM for a very local characterization, or dielectric measurements to determine the electrical conductivity… depending on the aimed property.Descriptors of the microstructure are very useful to put numbers to characterize the dispersion state. They can be used to quantify the effect of processing parameters during a mixing step or in next processing steps (injection…) on the microstructure [3-5], to detect the matrix degradation during the process [6]. The relationship between the microstructure descriptors and process parameters can allow to determine optimal processing conditions [7], keeping in mind the microstructure or property to be reached.The filler network is however highly sensitive to any flow, pressure and easily destroyed. Due to nanofiller interactions, the network can build-up again. These systems present a thixotropic character. Following the evolution of the moduli with time can be a good way to determine the dynamics of the network reconstruction [8-9]. The effect of the temperature on the network dynamics raises the question on the applicability of the time-temperature superposition principle. We showed that this superposition is only possible if the probed microstructure is the same. [8]The present poster will give an overview different information on the nanocomposite microstructure which can be accessed from the rheological characterization.References[1]W. Lertwimolnum, B. Vergnes, Polymer 2005, vol 46(10), 3462-3472 DOI[2]B. Vergnes, International Polymer Processing, 2011, vol 26, 229-232[3]W. Lertwimolnum, B. Vergnes, Polymer Engineering and Science 2006, vol 46, 314-323DOI[4]W. Lertwimolnum, B. Vergnes, Polymer Engineering and Science 2007, vol 47, 2100-2109 DOI[5]T. Domenech,, E. Peuvrel-Disdier, B. Vergnes, Composites Science and Technology 2013, vol 75, 7-14, DOI[6] G. Normand, E. Peuvrel-Disdier, B. Vergnes, Int. Polymer Processing, 2016, vol XXXI, 4, 508-516[7]G. Normand, E. Peuvrel-Disdier, B. Vergnes, Int. Polymer Processing, 2017, vol XXXII, 1, 129-137[8]R. Zouari, T. Domenech, B. Vergnes, E. Peuvrel-Disdier, Journal of Rheology 2012, vol 56, 725-742 HAL, DOI[9]T. Domenech,, R. Zouari, B. Vergnes, E. Peuvrel-Disdier, Macromolecules 2014, vol 47 (10), 3417–3427, DO