Multiwalled carbon nanotube microspheres from layer-by-layer assembly and calcination

Multiwalled carbon nanotube (MWNT) microspheres were fabricated by layer-by-layer (LBL) assembling of modified MWNTs and poly(diallyldimethylammonium chloride) (PDDA) via electrostatic interactions on poly(methacrylic acid) (PMAA) microspheres and subsequent calcination. The MWNT/PDDA film growth on planar substrates monitored by scanning electron microscopy (SEM) and UV-vis spectrophotometry demonstrated the success of uniform LBL assembly. SEM observations of the stepwise increase in MWNT thickness on PMAA microspheres with the increase of LBL cycle number indicated the efficiency of the spherical assembly. Upon calcination of the (MWNT/PDDA)/PMAA microspheres in air at 400 degrees C for 2 h to remove the PMAA templates, the resulting MWNTs exhibited microsphere morphology with diameters that are half those of their precursors. Transmission electron microscopic images revealed that the MWNT microspheres were not solid, but loose and porous. It is proposed that the MWNT layers shrink during the calcination and form such microsphere structure due to the van der Waals attractions between the nanotubes.