No abstract

Adsorbed polymer additives have been employed to reduce water content and improve cement workability through lowering viscosity, but the influence of over‐dosage and the presence of nonadsorbed chains have yet to be fully understood. Model magnesium oxide (MgO) suspensions were used to investigate the potential processing effect of “free” chain concentration on cementitious mixtures. The rheological impact of the free chains was measured through incorporation of nonadsorbing poly(ethylene glycol) (PEG) to suspensions stabilized with an adsorbed comb‐polymer superplasticizer. Analyses of the rheological data, that showed viscosity‐increases and viscosity‐reduction due to free PEG concentrations revealed a transition from depletion flocculation to depletion stabilization that contributed to the flow properties of the suspensions. The viscosity‐reduction observed for high concentrations of free chains may be useful for improved mixing of cements with free polymer in addition to the adsorbed polycarboxylate ether‐based superplasticizer. Additionally, the influence of free PEG on the macroscale flow behavior was also examined through local velocity measurements under shear. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45696.

Thermoforming processing, traditionally reserved for thermoplastic polymers and sheet metals, is extended here to boron‐based all‐ceramics. Specifically, sintered boron nitride composite sheets manufactured via a combined vibration and tape‐casting photopolymerization process exhibit a highly oriented microstructure that allows these preform sheets to flow as viscous Bingham pseudoplastics during compression molding. These sintered all‐ceramic preforms are thermoformed into thin, complex parts with features down to 200 µm. Further, a new workflow is leveraged to generate bespoke all‐ceramic heat spreaders that can be press‐fit onto printed circuit boards and outperform metal heat sinks as a low‐profile thermal management solution. This work offers a route for other all‐ceramics that may be thermoformed through first fabricating pre‐forms with highly‐ordered anisotropic microstructures.