(613c) Effect of the Shape and Relative Size of Building Blocks on the Properties of Hybrid Colloidal Gels

Here, we study colloidal gels based on charge-driven self-assembly between spherical and two-dimensional (2D) nanoparticles. Spherical gelatin polyampholyte nanoparticles (GelNP), with a diameter of around 300 nm, and 1-nm thick negatively charged 2D clays with different aspect ratios varying between 25 to about 3500 were used. The goal is to answer how the relative size of the building blocks can affect the microstructure and macroscopic properties of colloidal gels with asymmetric building blocks. We used synthetic silicate nanoplatelets (Laponite) with size ten times smaller than the GelNP, montmorillonite with a comparable size to the GelNP, and two other synthetic layered silicates with averages sizes that are 7 and 12 times larger than GelNP. Our results show that at a solid content of 5 wt.% and a GelNP/clay weight ratio of 1, gel formation takes place in all systems through charge-driven self-assembly. However, the hybrid gels exhibit distinct microstructures and viscoelasticity by changing the aspect ratio of the 2D building block. While in the case of the GelNP/Laponite system, the transition from liquid-like to solid-like behavior occurs via jamming of the Laponite-patched GelNPs, the bridging between the 2D clay nanosheets by GelNPs is the primary formation mechanism of the hybrid colloidal gel in the systems with high aspect ratio clays. Moreover, storage and loss moduli of the colloidal gels and their structural recovery increase with increasing the size of the clay nanosheets. The anisotropy of the building blocks and their interactions can alter the microstructure and the macroscopic properties of the colloidal gels and can be used to engineer soft materials with tunable properties. Specifically, a fundamental understanding of the self-assembly between spherical and 2D nanoparticles will enable designing injectable gels with controlled elasticity and flow properties for 4D bioprinting.