Design and assembly of chain-oriented-crystalline multilayered composite with largely improved mechanical strength

Design and assembly of organic/inorganic multilayered composite consisting of alternatively stacking of stiff inorganic platelets and soft organic polymers have great potential for developing next-generation lightweight high-strength materials. Beyond previous designs about the improvement of inorganic nanoplatelet alignment and inter-platelet bonding, a new design concept of control over the physical aggregation state of organic polymer chains within the multilayered structure for mechanical reinforcement is proposed. Based on a typical assembly system of nanoclay platelets and poly (vinyl alcohol) (PVA), a facile three-step process of gelation, uniaxial pre-stretching and evaporation is developed to construct chain-oriented-crystalline multilayered composite, in which the aggregation state of PVA including chain orientation (from 0.020 to 0.897), crystallinity (from 42.8 to 45.9%) and crystallite orientation (from 0.007 to 0.937%) is regulated successfully. These structural changes bring a 4.1-fold increase in the tensile strength of the multilayered composite because of substantial improvement in the strength of PVA layer that enlarges stress transfer from PVA to nanoclay platelets and leads to a failure mode change from the pull-out of nanoclay1 platelets to their fracture. These findings open an avenue for fabricating lightweight high-strength nanocomposites based on inorganic nanoplatelets and crystalline polymers.