Origins of saccharide-dependent hydration ataluminate, silicate, and aluminosilicate surfacesBenjamin J. Smitha, Aditya Rawala, Gary P. Funkhouserb, Lawrence R. Robertsc, Vijay Guptad,Jacob N. Israelachvilia,1, and Bradley F. Chmelkaa,1

aDepartment of Chemical Engineering, University of California, Santa Barbara, CA 93106; bHalliburton, Duncan, OK 73536; cRoberts Consulting Group,44 Windsor Avenue, Acton, MA 01720; and dRTI International, Research Triangle Park, NC 27709

Contributed by Jacob N. Israelachvili, March 25, 2011 (sent for review February 4, 2011)

Sugar molecules adsorbed at hydrated inorganic oxide surfacesoccur ubiquitously in nature and in technologically important ma-terials and processes, including marine biomineralization, cementhydration, corrosion inhibition, bioadhesion, and bone resorption.Among these examples, surprisingly diverse hydration behaviorsare observed for oxides in the presence of saccharides with closelyrelated compositions and structures. Glucose, sucrose, and malto-dextrin, for example, exhibit significant differences in their adsorp-tion selectivities and alkaline reaction properties on hydratingaluminate, silicate, and aluminosilicate surfaces that are shown tobe due to themolecular architectures of the saccharides. Solid-state1H, 13C, 29Si, and 27Al nuclear magnetic resonance (NMR) spectro-scopy measurements, including at very high magnetic fields (19 T),distinguish and quantify the different molecular species, their che-mical transformations, and their site-specific adsorption on differ-ent aluminate and silicate moieties. Two-dimensional NMR resultsestablish nonselective adsorption of glucose degradation productscontaining carboxylic acids on both hydrated silicates and alumi-nates. In contrast, sucrose adsorbs intact at hydrated silicate sitesand selectively at anhydrous, but not hydrated, aluminate moi-eties. Quantitative surface force measurements establish thatsucrose adsorbs strongly as multilayers on hydrated aluminosili-cate surfaces. The molecular structures and physicochemical prop-erties of the saccharides and their degradation species correlatewell with their adsorption behaviors. The results explain the dra-matically different effects that small amounts of different types ofsugars have on the rates at which aluminate, silicate, and alumino-silicate species hydrate, with important implications for diversematerials and applications.

Saccharide molecules and their interactions with inorganicoxide surfaces play crucial roles in a variety of natural and

synthetic processes, including biomineralization, biomoleculesynthesis, bone resorption, heterogeneous catalysis, corrosioninhibition, and cement hydration. For example, mono- and oligo-saccharides are thought to control the morphologies and struc-tures of carbonate skeletons in marine organisms through site-specific binding to the mineral phases (1, 2). Interactions ofsimple organic molecules with aluminosilicate surfaces and ex-changeable cations in clays have been hypothesized to be key fac-tors in abiotic syntheses of organic molecules (3). For example,sugar-silicate complexes have been shown to stabilize the abioticformation of biologically important sugars, such as ribose (4). Si-milar interactions are thought to promote the adhesion of marineorganisms at hydrated inorganic surfaces (5). Biofuels can be pro-duced when polysaccharides are converted to monosaccharidesand lower molecular weight alkenes at aluminosilicate zeolitesurfaces by heterogeneous reactions in the presence of water (6).Saccharides have also been found to inhibit the corrosion ofmetal surfaces by forming thin adsorbed layers that preventfurther oxidation (7). Finally, the hydration kinetics of alumino-silicate-based cements are critical to a number of modern tech-nologies, notably as synthetic structural materials for large-scaleconstruction projects and oil-well cementing, where saccharide

additives are used to slow hydration processes and alter rheolo-gical properties (8).

Although saccharide-inorganic materials are ubiquitous innature and used extensively in industry, saccharide interactionswith heterogeneous hydrating inorganic oxides are not well un-derstood at a molecular level. To a large extent, this has been dueto challenges associated with the molecular characterization ofthe complicated multicomponent, multiphase, and nonequili-brium systems in which they occur. Interestingly, large variationsin hydration behaviors of diverse oxides are observed in the pre-sence of chemically similar saccharides, which we hypothesize areassociated with subtle differences in their molecular interactionsat specific solid surface sites. Here, we establish the molecularbases by which closely related saccharides bind to different oxidesurfaces, identifying and correlating molecular interactions withspecific structural features that influence macroscopic hydrationproperties. In particular, the structural transformations of glu-cose and sucrose and their interactions with silicate, aluminate,and aluminosilicate surfaces are analyzed to establish the mole-cular properties and processes that govern hydration of thesetechnologically important materials.

Results and DiscussionSaccharide-Mediated Aluminate Hydration. The influences of differ-ent saccharides on the hydration of aluminates and silicates aredue to their different stabilities in alkaline solutions and in theiradsorption behaviors that depend on competitive interactionswith water at specific surface sites. At a micron-scale, saccharidesinfluence the morphological evolution of hydrating aluminateparticles, such as tricalcium aluminate (Ca3Al2O6, abbreviatedas “C3A” in cement chemistry). As shown in the scanning elec-tron microscopy (SEM) images of Fig. 1, very different crystalmorphologies are observed for the aluminate components follow-ing hydration for 4 h at 95 °C in the absence or presence of 1%glucose or sucrose, saccharides which have closely related mole-cular structures (Fig. 1). Initially, anhydrous C3A (Fig. 1A) con-sists of crystalline particles ranging in size from 1–20 μm thatrapidly hydrate in the presence of CaSO4 · 2H2O and withoutsaccharides to form a mixture of aluminate hydration products,primarily as 1–10 μm acicular crystallites (Fig. 1B). Such needle-like crystal morphologies are consistent with the formation ofettringite (Ca6Al2O6ðSO4Þ3 · 32H2O) and calcium aluminatemonosulfate (Ca4Al2O6ðSO4Þ · 12H2O, referred to as “mono-sulfate”), both of which form hexagonal crystals that are the ex-pected products of C3A hydration with calcium sulfate dihydrate(9). By comparison, Fig. 1C shows an SEM image of C3A

Author contributions: B.J.S., A.R., G.P.F., L.R.R., V.G., J.N.I., and B.F.C. designed research;B.J.S. and A.R. performed research; B.J.S., J.N.I., and B.F.C. analyzed data; and B.J.S.,G.P.F., L.R.R., V.G., J.N.I., and B.F.C. wrote the paper.

The authors declare no conflict of interest.1To whom correspondence should be addressed. E-mail: bradc@engineering.ucsb.edu andjacob@engineering.ucsb.edu.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1104526108/-/DCSupplemental.

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hydrated with 1% sucrose, which results in a notable decrease inthe quantity of aluminate-hydrate crystals and with numerousanhydrous C3A particles still present. Some acicular hydratesare observed, but the crystals are generally much fewer and smal-ler than those formed in the absence of saccharides (Fig. 1B). Incontrast, the crystal morphologies of C3A hydrated with 1% glu-cose (Fig. 1D) are very similar to those obtained without sacchar-ides (Fig. 1B), indicating that glucose has much less influencethan sucrose on the hydration of C3A.

Quantitative analyses of tricalcium aluminate hydration. The extentof C3A hydration and the quantities of different aluminate hydra-tion products can be established in detail by solid-state 1D and2D 27Al NMR measurements. At very high magnetic fields(18.8 T), single-pulse 1D 27Al magic angle spinning (MAS) NMRspectra of C3A hydrated without and with saccharides (Fig. S1)show signals from 27AlIV moieties in anhydrous C3A and 27AlVI

species into which the 27AlIV moieties are converted duringhydration. By comparing the relative integrated intensities ofthese signals, the extents of hydration can be estimated. In theabsence of saccharides, 74% of anhydrous 27AlIV moieties inC3A are converted into hydrated 27AlVI species (Table 1 andFig. S1A). In combination, solid-state single-pulse 27Al MASand 2D 27Alf1Hg heteronuclear correlation (HETCOR) NMRspectra (Fig. S2) allow different resolved 27AlVI species to beassigned and quantified in hydrated C3A. The 27Al peak assign-ments are based on previous studies (10, 11), and the 2D27Alf1HgHETCORmeasurements are consistent with the forma-tion of six-coordinate AlðOHÞ6 species, including ettringite(Fig. 2A), monosulfate, tricalcium aluminate hexahydrate(Ca3Al2O6 · 6H2O), and dicalcium aluminate octahydrate(Ca2Al2O5 · 8H2O).Without saccharides, ettringite (24%), mono-sulfate (19%), and Ca2Al2O5 · 8H2O (22%) are the dominant spe-cies, along with a minor fraction (9%) of Ca3Al2O6 · 6H2O

(Table 1). These analyses allow the extents of hydration and rela-tive quantities of aluminate hydration products to be comparedwith systems containing glucose, maltodextrin, and sucrose.

Notably, in the presence of small amounts of the differentsaccharides, the hydration of tricalcium aluminate is reducedby dramatically different extents under otherwise identical con-ditions. These differences are reflected in quantitative solid-statesingle-pulse 27Al NMR analyses (Fig. S1B–D) of C3A hydratedwith 1% glucose, maltodextrin, or sucrose. As measured bythe conversion of anhydrous 27AlIV to hydrated 27AlVI species(Table 1), sucrose most effectively inhibits overall C3A hydrationwith only 28% conversion, followed by maltodextrin (53%) andglucose (60%). These results are consistent with the distinct pro-duct morphologies observed in Fig. 1, manifesting the signifi-cantly different influences that these saccharides have on C3Ahydration. The relative quantities of the different aluminatehydration products are estimated from single-pulse 1D 27Al MASspectra (Fig. S3) and are shown in Table 1. All of the saccharidesexamined inhibit the formation of monosulfate, whereas only su-crose delays the formation of all aluminate hydrates to significantextents. All aluminate hydrates form directly from the hydrationof C3A, whereas monosulfate can also form from the subsequentconversion of ettringite. This suggests that sucrose adsorbs ontoC3A surfaces, thereby passivating hydration sites and inhibitingthe formation of other C3A hydration products.

Saccharide–aluminate interactions. The different aluminate hydra-tion behaviors in the presence of sucrose and glucose can be cor-related to their significantly different adsorption properties onC3A and its hydration products. Specific saccharide–aluminateinteractions in hydrated C3A can be probed by solid-state 2D13Cf1Hg HETCOR NMR measurements that are sensitive to di-pole–dipole couplings between 13C and 1H nuclei. For example,Fig. 3A shows the 2D 13Cf1Hg HETCOR spectrum acquired forC3A hydrated in the presence of 1% 13C-labeled glucose, inwhich correlated 2D signal intensity reveals interactions between13C and 1H moieties that are in molecular proximity (<1 nm).Compared to the 1D single-pulse 13C MAS NMR spectrum ofcrystalline glucose (Fig. 3A, Top), the absence of 13C intensitycorrelations at 92 and 95 ppm from C1α and C1β moieties, alongwith the appearance of 13C signals from carboxylate moieties(-COO-, 185 ppm), alkyl groups (-CH2-, 40 ppm; -CH3,20 ppm), and carbinol species (-CHOH, -COH, 55–85 ppm), es-tablish that the cyclic form of glucose has completely degraded.Such signals are consistent with the formation of saccharinic orother short-chained carboxylic acids, which have previously beenreported for glucose degradation in aqueous alkaline solu-tions (12).

Analysis of the intensity correlations in the 2D 13Cf1Hg HET-COR spectrum (Fig. 3A) of C3A hydrated in the presence ofglucose reveals specific interactions between glucose degradationspecies and aluminate hydration products. Strong intensity corre-lations are observed between the 13C carbinol signal centered at75 ppm and 1H signals at 3.6 and 1.5 ppm (Fig. 3A, right reddashed box) associated with the carbinol protons and hydroxylgroups from aluminate (27AlVI) hydration products (Fig. S2),

Fig. 1. Representative scanning electron micrographs of (A) anhydroustricalcium aluminate and hydrated for 4 h at 95 °C with (B) no saccharide,(C) 1% sucrose, or (D) 1% glucose by weight of C3A. The molecular structuresof the saccharides are shown. Hydration occurs in the presence of CaSO4 ·2H2O to moderate the otherwise rapid hydration of tricalcium aluminate.

Table 1. Relative populations of NMR-visible 27Al species and overall conversion of AlIV species in tricalcium aluminate to AlVI

products during hydration in the presence of saccharides

Saccharide

AlIV AlVI

% 27Alconversion

Ca3Al2O6 (C3A)50–80 ppm, %

Ca3Al2O6 · 6H2O11.0 ppm, %

ettringite10.0 ppm, %

monosulfate9.3 ppm, %

Ca2Al2O5 · 8H2O8.6 ppm, %

none 26 9 24 19 22 741% glucose 40 12 19 6 23 601% maltodextrin 47 12 15 4 22 531% sucrose 72 6 8 4 10 28

From quantitative line-fitting of 1D 27Al MAS NMR spectra in Figs. S1 and S3. Percent values are estimated to be accurate within �2%.

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respectively. This establishes that carbinol-containing glucosedegradation products adsorb strongly on aluminate-hydrate sur-faces, although the broadened 1H signal does not allow interac-tions with specific hydrates to be distinguished. Intensitycorrelations observed between the 13C signal at 185 ppm and 1Hprotons at 1.5 ppm (Fig. 3A, left red dashed box) show additionalmolecular interactions between -COO- moieties and aluminate-hydrate surfaces. Carboxylate groups in organic molecules likelybind to aluminate surfaces in aqueous environments throughelectrostatic interactions (Fig. 3A, Inset i), whereas carbinolmoieties form hydrogen bonds (Fig. 3A, Inset ii). Intensity corre-lations between 13C signals at 20 and 40 ppm associated with alkylspecies and the 1H signal at 1.5 ppm may result from intramole-cular (i.e., directly bonded -CH2- or -CH3 protons) or intermole-

cular (i.e., -AlOH) interactions. Both types of interactions areexpected to yield correlated signal intensity in similar regions ofthe 2D 13Cf1Hg HETCOR spectrum and are not resolved inFig. 3A. Intramolecular interactions account for intensity correla-tions between 13C signals at 185 and 40 ppm and the 1H signal at3.6 ppm associated with adjacent carbinol species. Using 13C-la-beled glucose, molecular interactions are thus observed betweencarboxylate and carbinol moieties found in glucose degradationproducts, providing direct evidence that these species adsorb onto,or are intercalated within, aluminate hydration products.

In contrast, similar measurements under identical alkalineconditions show that sucrose does not degrade and does notadsorb on aluminate hydration products. Fig. 3B shows the solid-state 2D 13Cf1Hg HETCOR spectrum of hydrated C3A in thepresence of 1% 13C-labeled sucrose that exhibits intensity corre-lations corresponding to dipole-dipole–coupled moieties asso-ciated with adsorbed sucrose molecules. All of the 13C signalsappear at similar chemical shifts, but are broadened, comparedto those observed in the 1D single-pulse 13C MAS NMR spec-trum of crystalline sucrose (Fig. 3B, Top), consistent with intactadsorption of sucrose on C3A. Intramolecular 2D intensity cor-relations are observed between multiple 13C signals and 1H sig-nals centered at 3.6 ppm that also are present in the solid-state2D 13Cf1Hg HETCOR spectrum of crystalline sucrose (Fig. S4).Importantly, no intensity correlations are observed between the13C signals and the 1H signal centered at 1.5 ppm (Fig. 3B, reddashed box) that are associated with -AlOH moieties, indicatingthat the 13C species are not in molecular proximity to aluminate-hydrate species. Unlike hydrating C3A systems containing glu-cose, the 2D 13Cf1Hg intensity correlations establish that sucrosedoes not bind to aluminate-hydrate surfaces, the formation ofwhich sucrose is notably most effective at inhibiting (Table 1).

Based on these results, we hypothesize that sucrose adsorbsintact selectively at C3A surfaces, thereby inhibiting C3A hydra-tion. In contrast, the degradation species associated with glucoseand maltodextrin adsorb nonselectively to aluminate hydrationproducts, resulting in the delayed formation of monosulfate, asdepicted schematically in Fig. 4. In alkaline solutions, the glucosering structure opens at the carbon 1–5 oxygen linkage (Fig. 3A),to form a linear structure with a carboxyl endgroup, beforedegrading further (12). By comparison, sucrose is composed ofglucose and fructose monomer units that are conjoined such thatsimilar ring opening does not occur because the carbon 1–7oxygen linkage prevents formation of a carboxyl moiety. This sug-gests that sucrose is a more effective hydration inhibitor becauseit selectively adsorbs at C3A surfaces, with its ring structure intact,resulting in higher local surface coverages, compared to glucoseor maltodextrin degradation species that also adsorb on diverse

Fig. 2. Schematic diagrams of (A) hydroxylated AlVI species in ettringite, and(B) the different four-coordinate Q1, Q2, and Q2L silicate moieties in CSH.

Fig. 3. Solid-state 2D 13Cf1Hg HETCOR NMR spectra acquired at 18.8 T,298 K, 10 kHz MAS for hydrated tricalcium aluminate (4 h, 95 °C) in the pre-sence of CaSO4 · 2H2O and with 1% (A) glucose or (B) sucrose by weight ofC3A. The Insets in (A) show glucose degradation moieties binding to alumi-nate surfaces through (i) -COO- interactions and (ii) -COH hydrogen bonds.

Fig. 4. Schematic diagrams depicting the different adsorption properties of(A) glucose degradation products (carboxylic acids, red) versus (B) sucrose(green) on tricalcium aluminate particles (gray) or aluminate hydration pro-ducts, e.g., ettringite (white hexagons) under alkaline conditions. Whereasthe glucose degradation species adsorb nonselectively, sucrose moleculesare selective for the anhydrous aluminate moieties.

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aluminate hydration products. The less-selective interactions ofcarboxylic acid species with aluminate hydration moieties arelikely a consequence of their much higher dissociation constants(e.g., saccharinic acids, pKa < 4.0 versus sucrose, pKa ¼ 12.6),which promote electrostatic interactions with cationic surfacesites. The combination of 1D and 2D NMR techniques providesimportant insights on saccharide-dependent aluminate hydrationand the molecular mechanisms that account for the distinctly dif-ferent saccharide behaviors.

Saccharide-Mediated Silicate Hydration. Quantitative analyses of tri-calcium silicate hydration. Similarly, the solution behaviors and/orstructural transformations of saccharides under alkaline condi-tions also lead to different binding configurations and coveragesat silicate surfaces that result in significantly different silicatehydration behaviors. As a technologically important example, thehydration of silicates such as tricalcium silicate (Ca3SiO5, oftenabbreviated as “C3S”), are primarily responsible for setting andstrength development of cements (9), which are often modifiedby saccharides that significantly affect bulk rheological or me-chanical properties. The extent of C3S hydration and formationof calcium-silicate-hydrate (“CSH,” Fig. 2B) products are eluci-dated by quantitative single-pulse 1D 29Si MAS NMR measure-ments, which show that certain saccharides more effectivelysuppress the formation of CSH during the early stages of hydra-tion than others. For example, the single-pulse 1D 29Si MASspectra of C3S hydrated for 4 h at 95 °C without and with sacchar-ides (Fig. S5) show 29Si signals from Q0 species (“Qn

” refers to29Si atoms that are covalently bonded via bridging oxygen atomsto n ≤ 4 other Si atoms) in anhydrous C3S that are convertedupon hydration to cross-linked Q1, Q2L, and Q2 silicate speciesassociated with CSH. Fig. 2B shows a postulated structure ofCSH that is consistent with previous 29Si NMR measurements(10), recent molecular modeling analyses (13, 14), small-angleneutron and X-ray scattering data (15, 16), and transmission elec-tron microscopy studies (17). In the absence of saccharides, theextent of hydration can be established by comparing the relativeintegrated 29Si NMR signal intensities fromQ0 (54%),Q1 (22%),Q2L (4%), and Q2 (20%) 29Si species, where hydration is mea-sured as the conversion of anhydrous 29SiQ0 to hydratedQ1,Q2L,and Q2 29Si species (Table 2 and Fig. S5A). Thus, under theseconditions, approximately 46% of the 29Si species have hydratedto form CSH. Similar analyses on C3S under otherwise identicalconditions, except containing 1% glucose, maltodextrin, or su-crose (Fig. S5 B–D), show that the conversion of 29Si Q0 speciesduring hydration is reduced for all saccharides to 24, 8, and 3%,for glucose, maltodextrin, and sucrose, respectively. These mea-surements establish the significantly different influences of thesesaccharides on C3S hydration, which follow the same sequence asobserved for the aluminates, but with greater effect.

Saccharide–silicate interactions.The molecular origins of the differ-ent tricalcium silicate hydration properties in the presence of thesaccharides are due to differences in their adsorption interactionsat specific silicate surface sites. Two-dimensional NMR measure-ments resolve interactions between water, organic moieties, and

silicate species that account for the suppression of cross-linked29Si species in hydrated C3S. For example, molecular interactionsbetween different silicate moieties and organic species are ob-served in the 2D 13Cf1Hg HETCOR spectrum of C3S hydratedin the presence of 1% 13C-labeled glucose (Fig. 5A). As with thealuminates, the absence of C1α and C1β 13C signals at 92 and95 ppm indicates that the cyclic form of glucose has completelydegraded, with the appearance of 13C signals at 182, 40, and20 ppm being consistent with the formation of saccharinic orshort-chained carboxylic acids. Intensity correlations are clearlyobserved between the carboxylate 13C signals at 172 and 182 ppmand the 1H signal at 1.3 ppm (Fig. 5A, left red dashed box) that isassociated with the hydrated 29Si Q1 and Q2 species (Fig. S6),along with the carbinol protons (3.6 ppm). Likewise, the carbinol13C signals centered at 75 ppm are correlated with the Q1 and Q2

silanol 1H signals at 1.3 ppm (Fig. 5A, right red dashed box) andthe carbinol 1H signal at 3.6 ppm. These observations providestrong evidence that the glucose degradation products adsorbstrongly on CSH surfaces and that both the -COO- and -COHmoieties are in close proximities to the surface -SiOH species.Carboxylate groups are expected to bind to silicate surfaces inaqueous environments through electrostatic interactions (Fig. 5A,Inset i), with carbinol moieties adsorbing via hydrogen bonds

Table 2. Relative populations of 29Si species and overall conversionof Q0 species in tricalcium silicate to cross-linked Q1, Q2L, and Q2

moieties during hydration in the presence of saccharides

Saccharide

Q0, % Q1, % Q2L, % Q2, % % 29Siconversion

> − 76 ppm −79 ppm −82 ppm −85 ppm

none 54 22 4 20 46 (±3)1% glucose 76 12 2 10 24 (±3)1% maltodextrin 92 4 1 3 8 (±1)1% sucrose 97 2 0 1 3 (±1)

From quantitative line-fitting of 1D 29Si MAS NMR spectra in Fig. S5.

Fig. 5. Solid-state 2D 13Cf1Hg HETCOR NMR spectra acquired at 11.7 T,298 K, 10 kHz MAS for hydrated tricalcium silicate (4 h, 95 °C) with 1%(A) glucose or (B) sucrose by weight of C3S. The Insets in (A) show glucosedegradation moieties binding to CSH surfaces through (i) -COO- interactionsand (ii) -COH hydrogen bonds. The Inset in (B) shows sucrose binding to CSHsurfaces through hydrogen bonds.

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(Fig. 5A, Inset ii). Weaker intensity correlations observed betweenthe 13C signals at 172, 182, and 75 ppm and the 1H signal at4.7 ppm indicate coadsorbed water in close proximity to the-COO- and -COH moieties. Weak intensity correlations betweenthese 13C signals and the 1H signal at 6.3 ppm result from nearbyhydrogen-bonded -OH moieties. Intramolecular interactions ac-count for the correlated intensity between 13C signals at 20 ppmand the 1H signal at 0.9 ppm associated with alkyl species (i.e.,-CH3, -CH2-). The molecular interactions between CSH moietiesand both -COH and -COO- groups establish that adsorbedglucose degradation products, as opposed to glucose itself, areresponsible for inhibiting C3S hydration.

Similar 2D NMR analyses of C3S hydrated in the presence ofsucrose manifest site-specific interactions between sucrose andsilicate hydration products. Fig. 5B shows 2D 13Cf1HgHETCORspectra of crystalline sucrose (red) and C3S hydrated with 1%13C-labeled sucrose (black), which are superimposed to empha-size similarities and differences in their correlated signals. Com-parison of the 13C signals in the 1D projections of crystallinesucrose and hydrated C3S establish that sucrose molecules adsorbintact with no degradation products observed (within the sensi-tivity limits of the measurements). Furthermore, strong intensitycorrelations are observed between all sucrose 13C signals and the1H signal at 1.3 ppm (Fig. 5B, black) associated with the hydratedQ1 and Q2 silanol species. This indicates that sucrose moleculesare adsorbed strongly at CSH surface sites in configurationswhere all of the carbon atoms can be in close (<1 nm) proximityto the hydrate surfaces. Intramolecular intensity correlations areobserved between multiple 13C signals and the 1H signal centeredat 3.6 ppm, which are also observed in the solid-state 2D 13Cf1HgHETCOR spectrum of crystalline sucrose (Fig. 5B, red). Weakerintensity correlations observed between the 13C signals at 67 and75 ppm and the 1H signal at 4.7 ppm indicate that some coad-sorbed water is also in close proximity to the sucrose molecules.However, compared to the 2D 13Cf1Hg HETCOR spectrum ofC3S hydrated with 1% glucose (Fig. 5A), these intensity correla-tions with water are significantly weaker, establishing that sucrosemore effectively excludes water from CSH surface sites.

Additionally, comparison of the 13C chemical shifts betweencrystalline sucrose (Fig. 5B, red) and sucrose adsorbed on CSH(Fig. 5B, black) allow specific 13C moieties that interact moststrongly with the hydrated silicate species to be identified. Whenan organic molecule binds to an inorganic ion or surface, the local13C electronic environments can be altered, leading to changes inthe 13C isotropic chemical shifts. For example, the isotropic 13Cchemical shifts of carbon atoms 7, 2, and 4 are each displacedby 2–3 ppm for the adsorbed species, compared to crystallinesucrose, whereas all other 13C shifts are nearly the same(jΔδj < 1 ppm). Importantly, this suggests that sucrose moleculesinteract via several carbon moieties with multiple CSH surfacesites (Fig. 5B, Inset) leading to stronger adsorption. Multiple in-teraction sites are expected similarly to promote sucrose adsorp-tion on C3S where -SiOH moieties are present under aqueousconditions, though in relatively low fractions that are challengingto observe. These measurements establish that, compared to glu-cose, sucrose more effectively inhibits C3S hydration, because ofthe presence of multiple interaction sites on (nondegraded)disaccharide molecules, which lead to strong sucrose adsorptionthat competitively excludes water at CSH sites.

Saccharide–Aluminosilicate Interaction Forces. The different mole-cular interactions of saccharides at aluminate and silicate surfacesobserved by 2D NMR similarly result in distinct adsorption andhydration behaviors at aluminosilicate surfaces. Surface forcesmeasurements, employing molecularly smooth aluminosilicatemica sheets, corroborate the molecular (<1 nm) NMR analysesand quantify longer-range (1–100 nm) forces between alumino-silicate surfaces hydrated in the presence of the different sacchar-

ides and/or their degradation products. For example, Fig. 6 showsnormal forces measured as functions of the distance separatingtwo aluminosilicate surfaces immersed in otherwise identicalalkaline solutions (pH 12.7, 25 °C) initially containing none or0.2 wt%, of the different saccharides. In the absence of sacchar-ides, the forces between the aluminosilicate surfaces are consis-tent with Derjaguin–Landau–Verwey–Overbeek (DLVO) theory(18), which describes the combination of attractive van der Waalsand repulsive electric double-layer forces that exist between twosurfaces in aqueous solutions. The characteristic decay length ofthe interaction, or Debye length (1∕κ), measured to be 1.5 nm(Fig. 6, Inset), is close to the value of 1.1 nm calculated fromDLVO theory (19). A so-called “hard wall,” where the repulsiveforce increases rapidly at very short separation distances, isobserved at approximately 1 nm, due to “steric-hydration” forcescaused by water and cations solvated at the mica surfaces. Thesurface forces apparatus (SFA) measurements permit quantita-tive comparisons to be made among different alkaline solutions,including those containing saccharides that may be adsorbed ontothe hydrated aluminosilicate mica surfaces.

Similar surface force measurements between mica surfaces incontact with alkaline solutions containing 0.2 wt% glucose orsucrose establish very different behaviors for the different sac-charides. As for the alkaline solution alone, the force-distanceprofiles for glucose and sucrose (Fig. 6) exhibit similar hard walls,though at significantly different separation distances of approxi-mately 1 nm for glucose and 7 nm for sucrose. For glucose, thehard wall at 1 nm is the same as that observed in the aqueoussolution without saccharides, indicating that most of the organicspecies have been removed from the mica. The hard-wall repul-sion at 1 nm provides quantitative evidence that the alkalineglucose degradation products adsorb relatively weakly on thealuminosilicate mica surfaces and can be “squeezed out” by fluidconvection as the mica surfaces approach molecular contact.

In contrast, for sucrose the 7-nm hard wall is significantlylarger than observed for glucose or the alkaline solution alone.This is due to steric forces between strongly adsorbed multilayersof sucrose molecules on the mica surfaces, which remain bound asthe surfaces are brought together, thereby presenting an addi-

Fig. 6. Representative repulsive force-distance profiles, FðDÞ, measurednormal on approach of two aluminosilicate mica surfaces immersed in other-wise identical 75 mM NaOH solutions (pH 12.7, 25 °C), but initially containingno saccharide, 0.2 wt% glucose, or 0.2 wt% sucrose. The Inset shows thesame data on a semilog scale for comparison with the exponential behaviorexpected for a repulsive electrostatic “double layer” (DLVO theory). A sche-matic diagram of adsorbed sucrose multilayers at small mica surface separa-tions is shown above.

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tional strong repulsive contribution. The binding of sucrose onsilicates established by solid-state NMR (Fig. 5B) suggests thatthe sucrose molecules adsorb in a planar fashion on the micasurfaces. This is similar to the stacking configuration of sucrosemolecules in its monoclinic crystal, which are separated by ap-proximately 0.8 nm (20). The 7-nm hard wall corresponds to mul-tiple layers (approximately 4–5) of strongly adsorbed sucrosemolecules on each mica surface (Fig. 6, Top), which remain intacteven at relatively high local pressures (≥10 atm). This establishesthat sucrose forms multilayers on the aluminosilicate surfaces,possibly through complexation with cations near the negativelycharged mica or by precipitation from the aqueous solution.

Quantitative analyses of the force-distance profiles for glucoseand sucrose indicate that complexation with cations occurs nearthe aluminosilicate surface and confirms strong sucrose adsorp-tion at the mica surfaces. Comparison of the force-distancecurves for glucose and sucrose (Fig. 6, Inset) reveals repulsiveinteractions with significantly different decay lengths as the micasurfaces approach, which reflect their different adsorption prop-erties on hydrated aluminosilicate mica, as similarly observed anddiscussed for the aluminates and silicates above. Longer-rangeinteractions observed at separation distances of about 40–100 nmare due to electrostatic interactions associated with the doublelayers near the surfaces of organic species adsorbed on the mica.The Debye lengths (1∕κ), determined directly from the slopesof the linefits in this region (Fig. 6, Inset), are approximately10 nm in the presence of sucrose or glucose. The longer Debyelengths, in comparison to alkaline solutions without saccharide(1∕κ ∼ 1.5 nm), are consistent with cation-saccharide complexa-tion near the anionic mica surfaces, which is expected to result indecreased overall concentrations of cations in the bulk solutions(e.g., κ ∝ ½Naþbulk�1∕2). The SFA results establish that sucroseadsorbs more strongly than glucose (or the latter’s associateddegradation products) and in multilayers (for a sufficiently highconcentration) on the aluminosilicate mica surfaces in aqueousalkaline media. Such strong adsorption appears to be enhancedby cation complexation and the multiple interaction sites estab-lished by the molecular-level NMR analyses.

ConclusionsThe very different hydration behaviors of aluminates, silicates,and aluminosilicates in the presence of the closely related sac-charides glucose, sucrose, and maltodextrin are shown to be dueto their different alkaline stabilities, adsorption selectivities atoxide surfaces, and binding strengths. Such different hydrationand adsorption properties are shown to be directly related tosubtle but important differences in the molecular structures ofthe saccharides. Solid-state NMR spectroscopy and surfaceforces measurements establish over complementary length scales(<1 nm and 1–100 nm, respectively) the transformations and

interactions of the respective mono- and disaccharide species atsilicate, aluminate, and aluminosilicate surfaces. Two-dimen-sional 13Cf1Hg HETCOR NMR spectra of hydrated tricalciumaluminate and silicate establish that glucose degradation speciesinteract nonselectively with aluminate and silicate hydration pro-ducts and suggest selective adsorption of sucrose at C3A surfacesites and multiple interactions with silicate hydrates. Quantitativesurface force measurements furthermore establish the formationof strongly adsorbed sucrose multilayers on hydrated aluminosi-licate surfaces that are stable at relatively high local pressures,compared to weak binding of glucose degradation species.

The advanced NMR and surface force techniques demon-strated here are applicable generally to other systems whereorganic species interact at heterogeneous aluminate, silicate, oraluminosilicate surfaces. Such measurements can be used to es-tablish molecular criteria for the design or selection of saccharidespecies that mediate surface reactions, such as hydration, corro-sion, or adhesion. The resulting insights are expected to contri-bute directly and broadly toward understanding the molecular-level interactions between saccharides and similar hydratingoxide surfaces, which occur in cements, biominerals, abioticsyntheses of organic molecules, heterogeneous catalysis of sugars,and corrosion inhibition.

Materials and MethodsTricalcium aluminate (Ca3Al2O6, CTLGroup), tricalcium silicate (Ca3SiO5,CTLGroup), and calcium sulfate dihydrate (gypsum, CaSO4 · 2H2O, Sigma-Aldrich) were used as received. D-glucose and sucrose, including 99%13C-enriched species, were obtained from Sigma-Aldrich and used as re-ceived. Maltodextrin (Main Street Ingredients) had a dextrose equivalentof 40. Hydrated materials were prepared by mixing the anhydrous materialsand saccharide species with water in a high shear blender (Fisher Scientific) at10,000 rpm for 1 min. The resulting mixtures were measured to be highlyalkaline, with pH values of 12.7 (�0.1). Water-to-solids mass ratios of 0.50and 2.00 were used for systems containing C3S, and C3A, respectively. Forthe cases where saccharides were present, they were added in concentrationsof 1.0% by weight of C3S or C3A. All C3A samples were hydrated with calciumsulfate dihydrate present in quantities of 50% by weight of C3A; all C3Ssamples were hydrated without gypsum. After mixing, all materials werepoured into polyethylene containers and hydrated for 4 h at 95 °C and100% relative humidity. Following hydration, the products were ground intoa powder, immersed in liquid N2, and evacuated at 0.10 Torr and 233 K toremove unreacted water and quench the hydration process (10). All NMRspectroscopy, SFA, and SEM experimental details are provided in SI Text.

ACKNOWLEDGMENTS. The authors thank C. Edwards, R. Prud’homme, andB. Figura for helpful discussions. This work was supported by a grant fromHalliburton, Inc. The measurements were conducted using the Central Facil-ities of the University of California, Santa Barbara Materials Research Labora-tory supported by the Materials Research Science and Engineering Centersprogram of the US National Science Foundation (Award DMR-05-20415).

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