Adsorption effects of polyethylene imine on the rheological properties for robocasting

SiC colloidal inks for the novel robocasting forming method were prepared using a two-step method, namely creating well-dispersed suspensions followed by inducing gelation via changing the pH values towards isoelectric points (IEPs). The effect of the adsorption behaviour of Polyethylene imine (PEI) on the rheological properties was systematically investigated for the both steps. Coincidentally, as SiC particles were saturated adsorbed with PEI, their respective rheological properties exhibited the optimum. For the first step, the strongest electrostatic repulsion was exhibited between SiC particles, and the corresponding suspension displayed the optimum dispersibility with a low shear viscosity (η0) of 27.86 Pa. For the second step, the colloidal gel presented the strongest elastic properties with an equilibrium storage modulus (G′) of 13,381.87 Pa and shear yield stress (τy) of 355.89 Pa. The colloidal gel ink with solid loading as high as 51 vol.% behaved in a yield-pseudoplastic manner and was successfully utilized to fabricate 3-D periodic lattice structures.