Origins of Saccharide-Dependent Hydration At Aluminate, Silicate, and Aluminosilicate Surfaces

Origins of Saccharide-Dependent Hydration at Aluminate, Silicate, and Aluminosilicate Surfaces

Benjamin J. Smith,¹ Aditya Rawal,¹ Gary P. Funkhouser,² Lawrence Roberts,³ Vijay Gupta,⁴ Jacob Israelachvili,¹ Bradley F. Chmelka^1*

¹ Department of Chemical Engineering, University of California, Santa Barbara, USA

²  Halliburton, Duncan, Oklahoma, USA

³ Roberts Consulting Group, Acton, Massachusetts, USA

⁴ RTI International, Research Triangle Park, North Carolina, USA

Competitive adsorption of water and organic species from homogeneous solution mixtures onto solid inorganic oxides are important in diverse natural and synthetic materials and processes. For example, organic additives are commonly used to slow surface hydration reactions and alter the rheological properties of cement-water mixtures. For this and related systems, however, the mechanisms by which different water and organic species react and/or interact at a molecular level with heterogeneous solids are not well understood. This has been due in part to challenges associated with the molecular characterization of multicomponent, non-equilibrium materials and processes.  In these systems, heterogeneous interactions of water and organic molecules occur at inorganic surfaces, which are often complicated mixtures of sites with different local compositions and structures.

For example, glucose, sucrose, and maltodextrin, although closely related saccharides, exhibit significant differences in their solution reaction properties, adsorption selectivities, binding strengths, and coverages on hydrating aluminate, silicate, and aluminosilicate surfaces that are shown to be due to their molecular architectures. Solution- and solid-state nuclear magnetic resonance (NMR) spectroscopy measurements distinguish and quantify the different molecular species, their chemical transformations, and their adsorption behaviors on different aluminate and silicate moieties. 2D NMR results establish non-selective adsorption of glucose degradation products containing linear carboxylic acids on both hydrated silicates and aluminates. In contrast, sucrose adsorbs intact at hydrated silicate sites and selectively at anhydrous, but not hydrated, aluminate moieties. Quantitative surface forces measurements establish relatively weak binding of glucose degradation species on hydrated aluminosilicate surfaces, whereas sucrose adsorbs strongly and forms multiple layers. The molecular structures and physicochemical properties of the saccharides and their degradation species correlate well with their adsorption behaviors and lead to different binding strengths and surface coverages on aluminosilicate-based cements. The analyses account for the dramatically different effects that different types of sugar molecules have on the rates at which aluminate, silicate, and aluminosilicate species hydrate. The resulting insights have important implications for cement hydration as well as related materials and applications, including marine biomineralization, abiotic biomolecule synthesis, bone resorption, heterogeneous catalysis, and corrosion inhibition.