Mechanical anisotropy of graphene nanocomposites induced by graphene alignment during stereolithography 3D printing

Abstract

Stereolithographically 3D-printed graphene-PMMA nanocomposites were previously found to be mechanically stiffer and stronger in the print axis, suggesting that the graphene filler was selectively oriented. Here, using polarized light microscopy, we confirm experimentally for the first time the presence of aligned graphene platelets in these nanocomposites. The alignment appears to be weak, however, as anisotropy of the storage modulus and quasistatic failure strength was only ~ 10% – 30%, about 100 × lower than the maximum anisotropy possible and 10 × smaller than that of other 3D-printed anisotropic composites. The optimal graphene concentration for maximum anisotropy was 0.02wt%– 0.05wt%, as graphene agglomeration at higher concentrations reduced anisotropy and beyond 0.2wt% it prevented 3D printing altogether. Using finite element simulations, which were experimentally verified, it was also shown that the anisotropy of the bulk nanocomposites could be fully imparted to more complex 3D-printed parts such as Octet Truss structures. Graphic abstract: [Figure not available: see fulltext.].