The key role of processing in tuning nonlinear viscoelastic properties and microwave absorption in CNT-based polymer nanocomposites

Multi-walled carbon nanotube (MWCNT)/polymer nanocomposites exhibit excellent microwave shielding properties by forming interconnected networks of MWCNT in the polymer matrix. However, the final properties of MWCNT-based nanocomposites greatly depend on the quality of MWCNT dispersion, and hence on the mixing technique. In the current work, for the first time, we show the effect of different mixing methods on nonlinear viscoelastic response and electromagnetic interference shielding effectiveness (EMI SE) of MWCNT/polymer nanocomposites. To do this, MWCNT/poly(styrene) (PS) nanocomposites were prepared by two frequently-used approaches, namely, melt mixing and solution mixing. Nonlinear rheological response of the samples reveals higher intra-cycle and inter-cycle viscoelastic nonlinearity for solution-mixed samples. Imaging analysis of the solution-mixed sample showed heterogeneous dispersion with highly interconnected networks of MWCNT in PS matrix. The interconnected network of MWCNT developed by solution mixing leads to significantly enhanced EMI shielding performance over melt-mixed nanocomposites containing big clusters of MWCNT in micro-scale but smaller agglomerates in nano-scale. Hence, an optimum state of dispersion (i.e., heterogeneous dispersion or small agglomerates connected with individual MWCNT) of MWCNT is necessary to achieve maximum EMI shielding performance.