Toughness and Fracture Properties in Nacre-Mimetic Clay/Polymer Nanocomposites

Nacre inspires researchers by combining stiffness with toughness by its unique microstructure of aligned aragonite platelets. This brick-and-mortar structure of reinforcing platelets separated with thin organic matrix has been replicated in numerous mimics that can be divided into two categories: microcomposites with aligned metal oxide microplatelets in polymer matrix, and nanocomposites with self-assembled nanoplatelets-usually clay or graphene oxide-and polymer. While microcomposites have shown exceptional fracture toughness, current fabrication methods have limited nacre-mimetic nanocomposites to thin films where fracture properties remained unexplored. Yet, fracture resistance is the defining property of nacre, therefore centrally important in any mimic. Furthermore, to make use of these properties in applications, bulk materials are required. Here, up to centimeter-thick nacre-mimetic clay/polymer nanocomposites are produced by the lamination of self-assembled films. The aligned clay nanoplatelets are separated by poly(vinyl alcohol) matrix, with 10⁶-10⁷ nanoplatelets on top of each other in the bulk plates. Fracture testing shows crack deflection and a fracture toughness of 3.4 MPa m^1/2, not far from nacre. Flexural tests show high stiffness (25 GPa) and strength (220 MPa) that, despite the hydrophilic constituents, are not substantially affected by exposure to humidity.