Rheological behavior of ZnO suspension with thermosensitive poly(N-isopropylacrylamide) for colloidal processing of ceramics

Novel colloidal processing using thermosensitive poly(N-isopropylacrylamide) (PNIPAM) as a coagulating agent has been developed to prepare complex-shaped ceramic components. In this work, the properties of PNIPAM aqueous solutions and the rheological behavior of ZnO suspensions with PNIPAM were investigated. The results show that the PNIPAM solutions exhibit obvious thermosensitivity and its transition temperature is around 32 °C. When the temperature is above 40 °C (Tc, the critical transition temperature of thermosensitive suspension), the 50% ZnO (volume fraction) suspension with 8 mg/mL PNIPAM has a sharp increase in viscosity and reaches up to 11.49 Pa·s at 50 °C, displaying strong elasticity. The main reasons are the increase of effective volume fraction attributed to precipitation of PNIPAM segments and the flocculation between ZnO powder particles. In addition, the maximum solid loading (volume fraction) at 20 °C is higher than that at 40 °C, which proves that the phase transition of PNIPAM can induce the flocculation of suspension.