Nanoscale brick and mortar strategy for mechanically strong multifunctional composites with extremely high filler-loading

To achieve the best physico-chemical properties of polymer composites, the concentration of fillers should be maximized in many cases. However, at extremely high concentrations of fillers, the discontinuity of the polymer matrix results in poor mechanical properties. To overcome this problem, we propose an efficient protocol to improve the mechanical strength significantly, even at an extremely high concentration of microscale fillers (graphite flakes, 95 wt%). Since the mechanical strength of the polymer composite strongly depends on both the homogeneous distribution of the polymer matrix around microscale fillers and the adhesion between them, we increased the mechanical strength of the composite by the preparation of a hybrid filler decorated with polymer nanoparticles. The decorated polymer nanoparticles eventually turned to the matrix during hot-pressing process like a mortar between bricks. Systematic studies on the mechanical strength as well as electrical and thermal conductivities of the composites revealed that both the precisely controlled size of the polymer nanoparticles and even distribution of them on the hybrid fillers were critical variables to enhance the material's properties above. The newly developed polymer composites with superior physical properties exhibited good electromagnetic interference shielding (EMI shielding effectiveness >80 dB in X-band, thickness ∼ 1.5 mm), making them suitable as electric heaters.