Ion Correlations\nDecrease Particle Aggregation Rate\nby Increasing Hydration Forces at Interfaces

The connection between solution structure, particle forces,\nand\nemergent phenomena at solid–liquid interfaces remains ambiguous.\nIn this case study on boehmite aggregation, we established a connection\nbetween interfacial solution structure, emerging hydration forces\nbetween two approaching particles, and the resulting structure and\nkinetics of particle aggregation. In contrast to expectations from\ncontinuum-based theories, we observed a nonmonotonic dependence of\nthe aggregation rate on the concentration of sodium chloride, nitrate,\nor nitrite, decreasing by 15-fold in 4 molal compared to 1 molal solutions.\nThese results are accompanied by an increase in repulsive hydration\nforces and interfacial oscillatory features from 0.27–0.31\nnm in 0.01 molal to 0.38–0.52 nm in 2 molal. Moreover, molecular\ndynamics (MD) simulations indicated that these changes correspond\nto enhanced ion correlations near the interface and produced loosely\nbound aggregates that retain electrolyte between the particles. We\nanticipate that these results will enable the prediction of particle\naggregation, attachment, and assembly, with broad relevance to interfacial\nphenomena.