(610b) Molecular Architectures of Organic Adsorbates Influence Hydration at Inorganic Oxide Surfaces

Competitive adsorption of dilute quantities (<1 wt%) of certain organic molecules and water at inorganic oxide surfaces strongly influence the rates of dissolution, hydration, and crystallization of inorganic species. Organic molecules, for example, saccharides and phosphonates, adsorb on heterogeneous low-surface-area (~1 m²/g) silicate and aluminate particles to inhibit hydration reactions in technologically important aluminosilicate cement-water mixtures. Such competitive adsorption of organic species in place of water slows the formation of silicate and aluminate hydration products that are responsible for the development of mechanical strength. The efficacies of different saccharide molecules to inhibit hydration at inorganic oxide surfaces depend on their molecular-level interactions, including hydrogen-bonding and electrostatic, at the solid-liquid interface. Such physicochemically distinct adsorption interactions of dilute saccharide species are elucidated by using solution- and solid-state nuclear magnetic resonance (NMR) spectroscopy, including with dynamic-nuclear-polarization (DNP) signal enhancements. The DNP-enhanced solid-state NMR measurements provide unprecedented improvements in signal sensitivity for near-surface species that are crucial for the detection and analysis of dilute (<1 wt%) organic adsorbates and silicate/aluminate species on low-surface-area (~1 m²/g) particles, which, until now, have been infeasible to characterize. The results establish that closely related disaccharides exhibit surprisingly different adsorption behaviors and corresponding hydration influences, which arise from their distinct site-specific surface interactions vis-à-vis water. Specifically, the adsorption behaviors of such disaccharides have been shown to depend on the relative extents and types of surface interactions (hydrogen-bonding versus electrostatic), which consequently depend on the molecular architectures, stereochemistries, and chemical reactions of the disaccharide molecules. Overall, the analyses and insights provide criteria for the rational design and use of organic adsorbates to mediate hydration processes in cement-water mixtures, which are crucial to ensure the fluidity of such mixtures, as is desirable for oilwell cementing applications.