With broad applications in fields from electronics to orthopedics, ceramic materials are valued for their high thermal conductivity and mechanical strength. Addition of non-adsorbing polymers to suspensions of ceramic particles enables adjustment of rheological properties such as viscosity and yield stress. Fabricating parts via 3D printing of polymer-ceramic suspensions has the potential to reduce material waste and produce complex designs, but print defects often result. These defects can be caused by a suboptimal choice of suspension—one of too high or low viscosity—thus printing objects that cannot hold their ideal shape. In this work, we examine how addition of non-adsorbing polymers can improve the 3D printing of ceramic suspensions. First, we measured the viscosity of aqueous solutions containing varying concentrations and molecular weights of polyvinylpyrrolidone to identify the overlap and entanglement concentrations at each molecular weight. Next, we prepared aqueous suspensions containing varied volume fractions and molecular weights of polyvinylpyrrolidone while keeping the volume fraction of alumina nanoparticles constant. Nanoparticle size and zeta potential measurements confirmed that polyvinylpyrrolidone does not adsorb on the alumina nanoparticles. Rheological tests were performed to characterize the viscosity and yield stress of each suspension. The same suspensions were then printed using direct ink writing (DIW), a type of 3D printing, to observe the final print quality. Comparing the rheological data with the respective prints allowed us to identify predictive flow parameters and determine optimal suspension composition(s) for DIW. We also identified compositions that were printable despite the presence of shear thickening - a dramatic jump in viscosity with increasing shear rate - due to this occurring at shear rates above that of extrusion. Finally, we related the suspension rheology and printability trends to the polymer conformation regimes identified by the initial solution viscosity measurements to further understand the dynamics of non-adsorbing polymers in concentrated suspensions. Our findings demonstrate how tuning the suspension composition can improve printing accuracy, and future research can apply lessons from this combination of materials to other printable polymer-ceramic suspensions.

Effects of non-adsorbing polymer addition on the rheology and printability of ceramic nanoparticle suspensions

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