Colloidal particle reaction and aggregation control in the Electrohydrodynamic 3D printing technology

The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. In this process, which is based on the formation of Taylor jet from a metallic ink, the investigation of particles reaction and aggregate formation in ink during printing is of great importance. In this paper, a new Finite Element model based on particle tracing in fluids is presented that couples the different physics that govern an EHD phenomenon. Vortex flow caused by boundary shear stress was observed in the ink jet; which was more like the Marangoni phenomenon in a stationary drop. By experimentally validating the presented model with the help of PIV technique, the effects of important parameters (volume fraction, number and size of particles, zeta potential, viscosity, voltage application rate) on aggregate formation were studied based on the DLVO theory. In general, any change of parameters that leads to the increase of volume fraction also boosts the amount of formed aggregates. No interaction effect was observed between the parameters of volume fraction, particle radius and number of particles. It was demonstrated that the DLVO theory by itself is not sufficient for determining colloidal ink stability, and that the parameters of volume fraction, radius and number of particles should also be investigated for this purpose. Considering the conditions of EHD printers, the amount of zeta potential needed for colloid stability increases significantly; and a minimum zeta potential of 110 mV is required for colloid stability. A too-low or too-high value of viscosity (mu > 500 mPa.s, mu < 3 mPa.s) and a low rate of applied voltage also lead to reduced aggregation.

Automated summary

EHD 3D printing technology utilizes metallic ink to form Taylor jets for manufacturing submicron-size structures, with a focus on studying particles reaction and aggregate formation in ink during printing. Experimentally validated Finite Element model revealed vortex flow in ink jet and the impact of key parameters on aggregate formation.