Effect of Dispersion on Rheology and 3D Printing of Chitosan-Graphene-Titanium Dioxide Composites

Three-dimensional printing is renowned for its ability to produce complex geometries. By utilizing a pressure-driven additive manufacturing (AM) process called direct ink write (DIW) with polymer composite ink, it is possible to create parts with tailored internal microstructures that enhance surface area and particle-particle adsorption kinetics for water remediation applications. However, DIW of particle-filled systems faces challenges, particularly nozzle clogging. This paper explores the relationship between dispersion of aggregate size, torsional rheology, and the capacity to print relatively highly particle-filled systems. Various characterization methods, including torsional rheology, dynamic light scattering (DLS), and field emission scanning electron microscopy (FESEM) were employed utilizing a chitosan-graphene-titanium dioxide (CS-G-TiO2) polymer composite ink composed of TiO2 nanoparticles (1 wt.% to 25 wt.%), graphene (1 wt.%), and chitosan (5 wt.% to 9 wt.%) to evaluate the effect of ultrasonication techniques (bath vs. probe) on aggregate size. Probe-sonicated dispersions showed a more narrow monodispersed and unimodal aggregate size distribution with a primary average aggregate size of 255 nm. In contrast, bath-sonicated dispersions exhibited a moderately polydispersed, trimodal distribution with modes centered at 90 nm, 295 nm, and 5.6 μm. Non-Newtonian rheological parameters such as yield stress, complex viscosity, storage, and loss moduli were higher for the probe-sonicated CS-G-TiO2 composite ink than for the bath-sonicated CS-G-TiO2 composite ink. This increase is likely attributed to enhanced particle interactions, which allow for greater CS adsorption. These findings offer valuable insights into optimizing formulations for desired rheological properties in DIW printing. The results enable the direct ink writing of intricate geometries with high surface areas and less shape distortion, providing significant insights into processing similar multi-component slurry-based composite inks for DIW.