Self-assembly of covalently bonded nano-silicates with controllable modulus and thermal stability

Modified vermiculites (MVMTs) that self-assembled into fiber or nacre-like structures were fabricated by covalent bonding with hexamethylene adipamide (HA) during in situ polymerization. Unlike previous researches where self-assembled silicates have been fabricated via physical interactions, covalent bonding of vermiculites demonstrated in this research provided substantially higher mechanical properties and thermal resistance to the assembled materials. In addition, the shape and size of the self-assembled structures could be controlled by varying the amount of coupling agent and the modulus of the fiber-like assemblies could be controlled by heating. X-ray Photon Spectroscopy proved the covalent attachment of the HA onto vermiculites. At low concentrations (11%) of coupling agent, the MVMTs self-assembled into fiber like structure and into nacre-like structures at a coupling agent concentration of 17% thereby enabling us to control the shape and size of the self-assemblies. Atomic force microscope measurements showed that the elastic modulus of the self-assemblies were about 17-18 GPa, compared to the modulus of 0.3 and 1.5 GPa for the pure polymer and unmodified clay, respectively. The ability to covalently bond and control the self-assemblies and the resulting high performance properties of the self-assemblies could be useful to develop materials for various applications.