Non-additive Stabilization of Aqueous Alumina Suspensions by Binary Peg-Ester Dispersants: Composition Dependence, Phase Partitioning and Ph Response

Abstract

Background: Stable aqueous alumina suspensions depend strongly on the molecular architecture and relative proportion of adsorbing dispersants.

Methods: Two polyethylene-glycol (PEG) esterification-product families were investigated: an acrylic-acid/PEG product (X) and a citric-acid/PEG product (Y). Results: Orthogonal screening identified X9 and Y7 as the best-performing individual products, giving 24 h phase-separation indices (PSI24) of 9.0% and 11.8%, respectively, compared with 30% for citric acid and 58% for the additive-free suspension. Binary blending produced a pronounced non-additive composition response. At a fixed total dispersant content of 1 wt%, the 60/40 X/Y formulation reached PSI24 = 5.3%, corresponding to a 41.1% reduction relative to X9 and a 47.6% reduction relative to the linear-mixture expectation. The favorable response extended across a broad composition interval, with blends containing 20-80% X outperforming X9. Phase partitioning showed that the improvement was governed primarily by suppression of clarification: at 60/40, the clear-supernatant fraction decreased to 5.00% while the compact-sediment fraction remained at 0.25%, increasing the retained-suspension fraction to 94.75%. The optimized blend also exhibited a pronounced near-neutral pH response, with PSI24 = 5.0% at pH 6 and values no higher than 6.3% over pH 5-7. The composition and pH dependences are consistent with complementary carboxylate adsorption, charge regulation, competitive surface occupation, and PEG-mediated steric hydration.

Conclusion: These results demonstrate that binary PEG-ester dispersants can generate composition-specific stabilization substantially exceeding the
performance expected from simple endpoint averaging.