(757g) 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

⁴RTI 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.