Effect of reinforcements mechanical properties on the performance of anisotropic colloidal crystal composites

Abstract Overcoming the conventional trade‐off between strength and toughness is the long‐term goal in structural materials. One way to break this trade‐off is to get inspiration from biological materials in which delicately tailored microstructures elicit unusual properties. For example, by manipulating the packing of mineralized building blocks over centimeter scale and their interfaces, nacre triggers process zone toughening, a toughening mechanism that increases its toughness well beyond its constituents and even leads to pseudo plastic macroscopic behavior. Anisotropic colloidal crystal composites, in which monodispersed silica rods are assembled into densely packed and ordered microstructure, are an excellent way to study the emergence and potency of this process zone toughening. In this study, we investigate whether the mechanical properties of the silica rods can be improved by heat treating the mineral building blocks and its effect on the toughening mechanisms. After heat treatment at different temperatures from 600 to 1300°C, silica rods treated at 600°C were found to maintain the original shape and to enable the assembly of anisotropic colloidal crystal composites with an 80% volume fraction of minerals. The flexural strength and modulus of individual rods were determined as 1.4 ± 0.5 and 20.9 ± 10.7 GPa, respectively, using a scanning electron microscopy in situ micro‐bending test. We compare Young's modulus, strength, and toughness values of the colloidal crystal composites obtained before and after heat treatment through nanoindentation and three‐point bending tests. Our findings show that heat treatment effectively increases the maximum strength by 40%, doubles Young's modulus and toughness while maintaining the damage delocalization toughening mechanism over millimeters.