Shaping Calcite Crystals by Means of Comb Polyelectrolytes Having

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Shaping Calcite Crystals by Means of Comb Polyelectrolytes Having Neutral Hydrophilic Teeth Danilo Malferrari,† Simona Fermani,‡ Paola Galletti,†,‡ Marco Goisis,§ Emilio Tagliavini,†,‡ and Giuseppe Falini*,†,‡ †

Centro Interdipartimentale di Ricerca in Scienze Ambientali Sede di Ravenna-Università di Bologna, via S. Alberto 163, 48100 Ravenna Italy ‡ Dipartimento di Chimica “G. Ciamician” Alma Mater Studiorum, Università di Bologna, via Selmi 2, 40126 Bologna, Italy § Italcementi, Direzione Innovazione, via Stezzano 87, 24126, Bergamo, Italy S Supporting Information *

ABSTRACT: Comb polyelectrolytes (CPs) having neutral hydrophilic teeth, similar to double hydrophilic block copolymers, are a powerful tool to modify the chemical−physical properties of inorganic crystalline materials. One of their main applications is in concrete technology, where they work as superplasticizers, particledispersing agents. Here, CPs, having the same poly(acrylic acid) (PAA) backbone chain and differing in the grafting with methoxy poly(ethylene glycol) chains (MPEG) of two molecular weights, were used to investigate the influence of tooth chains in polymer aggregation and in control on morphology and aggregation of calcite particles. These polymers aggregate, forming interpolymer hydrogen bonds between carboxylic groups and ether oxygen functionalities. The presence of calcium ions in solution further enhances aggregation. Crystallization experiments of calcite in the presence of CPs show that the specificity of interactions between polymers and crystal planes and control on aggregation and size of particles is a function of the content and chain length of the MPEG in the PAA backbone. These parameters limit and can make specific the electrostatic interactions with ionic crystalline planes. Moreover, the mechanism of crystallization, classical or nonclassical, is addressed by the CP structure and concentration. These findings have implications in the understanding of the complex chemical processes associated to concrete superplasticizers action and in the study of the biomineralization processes, where biological comb polyelectrolytes, the acidic glycoproteins, govern formation of calcitic structures.

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INTRODUCTION

anionic comb copolymers with a charged backbone and grafted hydrophilic side chains have proven to be very effective.13 The anionic backbones are found to adsorb onto the negatively charged cement surface through positive calcium ions bridging.14−16 The hydrophilic neutral side chains provide the required entropy15 (steric hindrance) to overcome ion correlation forces, which otherwise cause the cement grains, covered by cement nanohydrates, to aggregate.17 The result is a drastic widening of the workability window and decrease of water/cement ratio which permit one to get a high-performance material with enhanced consistence retention, durability, and mechanical properties. CPs show several analogies with double hydrophilic block copolymers (DHBCs).18,19 Both polymers consist of one hydrophilic block, having the features of a negatively charged polyelectrolyte, able to interact with inorganic minerals and

Comb polyelectrolytes (CPs) can be synthesized in a wide variety of well-defined topologies1 and provide a tool to control the stability and viscoelastic properties of colloidal suspensions,2,3 surface hydrophobicity,4 colloid crystallization, and crystal morphology.5−8 CP solutions capability to interact with substrates depends on their structure and dynamics, issues which provide many open questions. This is due to a series of complicating factors which are implicit in CP composition, including noncrystallinity and long-range charge interactions.9,10 In methoxy poly(ethylene glycol)-grafted poly(acrylic acid) (PAA-g-MPEG) the neutral hydrophilic PEG tooth chains can make intra- and intermolecular hydrogen bonds with the carboxylic groups of the PAA backbone.11 This interaction is a function of a series of parameters depending on the polymer, like the degree of grafting and concentration, and on the solution, like pH and ionic strength. CPs are currently used as stabilizers and superplasticizers of colloidal particles in cementitious materials.12 In particular, © 2013 American Chemical Society

Received: November 20, 2012 Revised: January 10, 2013 Published: January 15, 2013 1938

dx.doi.org/10.1021/la304618f | Langmuir 2013, 29, 1938−1947

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surfaces, and another hydrophilic block that does not interact (or only weakly) with mineral and surfaces and mainly promotes solubilization in water. The main difference is in the spatial organization of these two blocks; in the DHBCs the two blocks are sequentially alternated, while in CPs the not interacting hydrophilic blocks are randomly bounded along a polyelectrolytic block. It has been widely demonstrated that the DHBCs are extraordinarily effective in crystallization control of many minerals, among them calcium carbonate,19−30 calcium phosphate,31 barium sulfate,32,33 and zinc oxide.34 On the contrary, CPs have been applied to modulate only the shape and aggregation of calcite6,7 and zinc oxide8 crystals. These particles, sometimes having morphologies and diffraction properties as single crystals, can be obtained from solutions either by classical or by nonclassical crystallization pathways.28 In the former, crystal growth occurs by lattice aggregation of atom/ion/molecule and the final single crystals show flat surfaces. In the latter, formation of particles is obtained by association of preformed nanoparticles. Their registered tridimensional aggregation produces crystals, called mesocrystals,23−26 which show a high surface roughness. These crystals diffract as single crystals obtained by the classical crystallization process. The solution supersaturation and presence of additives can discriminate between the two mechanisms.25−28 It has been also shown that adsorption of CPs occurs as a result of entropy gain owing to the release of counterions and water molecules, whereas linear polyelectrolytes adsorb because of strong electrostatic attraction into the CaCO3 surface.35,36 Here three PAA-g-MPEG CPs (CP1−3) were used as additives in calcite crystallization experiments. They share the same PAA backbone but differ in the molecular weight of the grafted MPEG chains and in the grafting degree. The goals of this research are to get knowledge on the structures of CP1−3 by analysis of their association in different environments and their capability to control the morphology and association of calcite crystals.

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Table 1. Features of the Polyacrylic Acid, Methoxy Poly(ethylene glycol), and Comb Polyeletrolytes Used in the Calcium Carbonate Crystallization Experiments code

chemical composition

PAA MPEG1000

poly(acrylic acid) methoxy poly(ethylene glycol) methoxy poly(ethylene glycol) MPEG1000 grafted PAA MPEG1000 grafted PAA MPEG3000 grafted PAA

MPEG3000 CP1 CP2 CP3

grafting degree (%)a

Mw (Da)b 5000 1000

pKa 4.537

3000 48

39000

5.8(1)

34

29000

5.6(1)

22

51000

5.6(1)

a

The degree of grafting was evaluated through the measured molecular weight; it is expressed as percentage of the grafted carboxylic positions. b The average molecular weights of the comb polyelectrolytes have been determined by GPC. crystallization experiments continued for 15 or 30 days. The obtained crystals were washed twice with deionized water (750 μL for well), and then the microplates were air dried for 2 days at room temperature. In each crystallization experiment a control well containing pure calcium chloride solution was present. Crystals grown in the absence of polymeric additives were always perfect rhombohedra. Characterization Methods. The weight-average molecular weight (Mw) was measured by GPC-TDA (Viscotek TDA) equipped with refractive index, viscometer, and right angle light scattering (RALS). Addition of light scattering permits one to eliminate column calibration to give absolute molecular weights. From the practical point of view, the PEO standard supplied by the producer (dissolved in the 0.1 M NaNO3 aqueous mobile phase) was injected in the column and the chemical−physical parameters (Mw, C, dn/dc, and IV) of the standard were introduced in the OmniSEC software in order to create the blank method. Analysis of the unknown samples relies on the blank method and requires the correct dn/dc value for each chemical. For the homopolymers, i.e., PAA and MPEG, it was obtained from the literature; for the copolymer, i.e., PAA-grafted MPEG, it was calculated by the software after injecting 3−5 solutions at known concentration. Dynamic light scattering was used for determination of the polymeric molecules size distributions employing a Malvern Nano ZS instrument with a 633 nm laser diode. Experiments were carried at 25 °C in a quartz cuvette of 1 cm optical path length. A Leica transmission optical microscope was used to obtain images of CaCO3 crystals grown in the presence of comb polyelectrolytes. Sample was placed on a microscope slide beneath a standard glass coverslip and observed under bright-field conditions with crossed polarizers. Images were captured with a CCD digital camera and recorded using software (LAS EZ) supplied by Leica Microsystems. Image analysis was conducted on the cross-polarized optical micrographs to derive data for the crystallite birefringence. The dried glass coverslips covered with crystals were glued to SEM aluminum stubs. After gold coating, crystals were observed in the Phenom and Hitachi FEG 6400 scanning electron microscopes. The X-ray powder diffraction patterns were recorded using a Philips X’Celerator diffractometer with Cu Ka radiation (λ = 1.5418 Å) and a Ni filter. Samples were scanned for 2θ angles between 20° and 60°, with a resolution of 0.02°. Crystals were analyzed directly on the glass substrates, where they have been deposited without any mechanical treatment. In this way, the preferential orientation of the crystals was kept. FTIR spectra were collected on powdered samples (approximately 0.5 mg) of crystals mixed with about 100 mg of anhydrous KBr. Mixtures were pressed into 7 mm diameter discs. Pure KBr discs were used as a background. FTIR spectra of CP1−3 were collected from lyophilized samples, while those of mineral particles from the material mechanically removed from the glass coverslip. Analysis was performed at 4 cm−1 resolution using a Nicolet 380 FT-IR spectrometer. Thermogravimetric

MATERIALS AND METHODS

Materials. Calcium chloride dihydrate and anhydrous calcium chloride granular (for drying) manufactured by Merck Co. were used. Ammonium carbonate was supplied by Sigma Co. Aqueous solutions were prepared using Milli-Q water (resistivity 18.2 MΩ cm at 25 °C; filtered through a 0.22 μm membrane). Comb polyelectrolytes are reported in Table 1 and were supplied by the ITC Group. Calcium carbonate crystallizations were carried out using microplates, 24 wells (diameter 16 mm) with Lid, tissue culture treated polystyrene supplied by IWAK brand, and glass cover round slides (12 mm). Crystallization Method. A microplate with 24 wells was prepared placing an ethanol-washed and postdried glass cover slide in each well. Then a total volume of 0.75 mL of 10.0 mM calcium chloride solution was put on the glass cover slide of each well. After this, the wells, each filled with the respective calcium chloride solution, were covered with aluminum foil that was punctured with a needle to enable gas diffusion. Then the microplate was placed inside a Plexiglas box containing ammonium carbonate and anhydrous calcium chloride. When the effect of the polymeric admixtures was studied, 10 mM calcium chloride solutions containing the respective additive were used. Stock solutions of CP1−3, which were 10 mM with calcium chloride, were diluted with 10.0 mM calcium chloride solution to the required concentrations of CP1−3. The crystallization process started with the vapor diffusion of CO2 and NH3 from ammonium carbonate in the calcium chloride solutions at room temperature. After 4 days the crystallizations were stopped by opening the Plexiglas box. Some 1939


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Figure 1. Schematic representation of chemical structure of PAA-g-MPEG CPs (CP1−3) used as additives in calcium carbonate crystallization experiments. They share the same PAA backbone (in red), but differ in the molecular weight of the grafted MPEG chains (in blue) and in the grafting degree. investigations were carried out on dried samples using Instruments SDT 2960 at a heating rate of 10 °C/min in a nitrogen atmosphere over a temperature range of room temperature from 30 to 600 °C. Sample weights were 3−5 mg, and the nitrogen flow rate was 100 mL/ min.

Table 2. Hydrodynamic Radius (nm) Determined by a Measure of Dynamic Light Scattering of PEG1000, PEG3000, PAA, CP1, CP2, and CP3 in 10 mM Calcium Chloride Solution and in Buffered Solutions at pH 9.0, 7.0, and 4.0a

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RESULTS In Table 1 the chemical features of CP1−3 (Figure 1) are reported. CP1 and CP2 were obtained by a grafting process on the 5 kDa PAA chain with 1 kDa MPEG chains in 48% and 34% of the carboxylic functional groups, respectively; a similar grafting of 22% of the carboxylic functional groups with 3 kDa MPEG produced CP3. MPEG grafting along the PAA chain is random. CP1−3 were soluble in water and in a 10 mM CaCl2 solution over the range of studied concentration. The presence of the MPEG-grafted chains changed the acidity of the PAA chain. Indeed, the pKa value of CP1, CP2, and CP3, determined by volumetric titration, was 5.8, 5.6, and 5.6 respectively (Figure S1, Supporting Information). These values were higher than that of the PAA chain (4.5).37 DLS and FTIR were used to study the association of the PAA, CP1, CP2, and CP3 in a 10 mM CaCl2 solution or in buffered solutions at pH 4.0, 7.0, and 9.0. Results are summarized in Tables 2 and 3. The hydrodynamic radius (HR) of the PAA is almost constant (2.2−2.9 nm) in solutions having different pHs, above and below the pKa of the carboxylic groups (about 4.5), but drastically increases to 13.8 nm in the presence of calcium ions. On the contrary, the HR of the CPs significantly varied in solutions having different pHs and, as observed for PAA, increases assuming the highest values in the presence of calcium ions. Moving from the acidic condition to the basic one a general reduction of the HR was observed. However, the HR of CP1 was higher at pH 7.0 than at pH 4.0 or 9.0. CP3 showed the highest values of HR and the most significant increase due to addition of calcium ions from 4.8 to 14.1 nm. HR of the MPEG molecules did not change in solutions having different pHs and in the 10 mM CaCl2 solution. FTIR spectra were collected from polymer samples obtained from solutions having pH 4.0, 7.0 and 9.0 and from the 10 mM CaCl2 solution. The carboxylate functionality of PAA and functional groups of MPEG have characteristic absorption bands in the 500−2000 cm−1 region of the infrared spectrum (Figure S2, Supporting Information). The diagnostic vibration

code

10 mM CaCl2b

pH 4.0

pH 7.0

pH 9.0

PEG1000 PEG3000 PAA CP1 CP2 CP3

2.9 3.1 13.8 6.7 6.1 14.1

2.0 3.1 2.8 4.3 5.6 8.3

1.8 3.1 3.1 4.7 4.5 4.8

1.7 3.0 2.2 3.4 4.1 4.1

a

A polymer concentration of 1.0 , 3.0, 5.4, 2.6, 3.9, and 3.6 mg/mL of PEG1000, PEG3000, PAA, CP1, CP2, and CP3, respectively, was used. These concentrations were those used in the calcite crystallization experiments. bThe polymeric 10 mM CaCl2 solutions were not buffered, and the corresponding pH values were 5.6, 5.5, 3.9, 4.7, 4.0, and 4.6 for PEG1000, PEG3000, PAA, CP1, CP2, and CP3, respectively.

frequencies are those of the carboxylic stretching, the carboxylate symmetric and antisymmetric stretching, and the OH bending. Peak wavenumber maxima and their relative intensities measured from samples obtained in the different conditions are reported in Table 3. As consequence of the increase of pH, the intensity of the absorption band due to carboxylic groups decreased (1730 cm−1) while that one due to carboxylate groups (1410 cm−1) increased. Moreover, absorption maximum of the carboxylic stretching peak shifts to lower wavenumbers. The OH bending absorption band decreased in intensity increasing the pH, unless in CP2 where it was stronger at pH 7.0 than at pH 4.0 or 9.0. After addition of calcium ions at the CPs solutions the FTIR spectra showed profiles similar to those observed at pH 4.0, unless a very small shift to lower wavenumbers of the carboxylic group absorption band. Calcite crystals were precipitated using diffusion of CO2 and NH3 from ammonium carbonate into solutions of calcium chloride containing CP1−3. In a control experiment pure calcite was precipitated in the absence of additives. The effects of PAA and MPEG, the CP1−3 constituents, on crystallization of calcium carbonate are illustrated in the Supporting 1940


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process of ripening was observed: the big crystals partially dissolved in their less stable regions and the small ones dissolved almost completely. Dissolution provoked overgrowth of calcium carbonate in a more stable phase, pure calcite crystals, on the surfaces of the big crystals. The two sets of samples gave similar results when analyzed by FTIR and XRD but showed a different number of crystals when observed by OM. The following data refer to the samples analyzed just after the crystallization process was stopped, where a higher crystallization density is present. Figure 2 shows optical micrographs, taken between crossed polarizers, of the calcite crystals grown in the presence of CPs.

Table 3. FTIR Absorption Bands of the CPs in a Solution Having pH 4.0, 7.0 or 9.0 and in a 10 mM CaCl2 Solutiona code

solution

CP1

pH 4.0 pH 7.0 pH 9.0 10 mM CaCl2 pH 4.0 pH 7.0 pH 9.0 10 mM CaCl2 pH 4.0 pH 7.0 pH 9.0 10 mM CaCl2

CP2

CP3

carboxylic stretchingb

carboxylate sym. stretching

1732 1727 1728 1730

(s) (m) (m) (s)

1574 (m) 1581 (s)

1642 1644 1644 1644

(m) (s) (w) (m)

1410 (w m) 1408 (m)

1730 1730 1726 1729

(s) (m) (w) (s)

1576 (s) 1578 (s)

1644 1644 1644 1644

(m) (w) (w) (w)

1409 (w m) 1411 (m)

1731 1726 1726 1728

(s) (w) (w) (s)

1575 (m) 1580 (m)

OH bending

1644 (m) 1644 (m)

carboxylate asym. stretching

1410 (m) 1411 (m)

1644 (m)

a

Their relative intensity is indicated in brackets: strong (s), medium (m), or weak (w). bThe carboxylic stretching band has also a contribution from the stretching of the ester bonds formed in the grafting process.

Information (Figures S3 and S4) and consistent with data reported in previous works.6,38 The MPEG molecules in entire range of studied concentration did not affect precipitation of calcium carbonate. Only precipitation of a rhombohedral single crystal of calcite was observed. In the presence of PAA, precipitation of two families of particles was observed. At the lowest concentration, 10 μg/mL, aggregates generated by assembly of single crystals of calcite appeared. These aggregates increased in their size almost losing their crystalline morphology when the concentration increased at 0.1 mg/mL, as already reported.6 In this condition also precipitation of rounded particles without any crystalline appearance was observed. This last species was the unique one observed when the concentration of PAA was 2.5 mg/mL. In this work the effect of each CP1−3 on calcium carbonate precipitation was screened over a range of concentrations. Here, the results at two limit concentrations, 0.05 and 2.5 mg/ mL, 0.078 and 3.9 mg/mL, and 0.072 and 3.6 mg/mL, for CP1, CP2, and CP3, respectively, are reported. The lower concentration (cmin) was minimal to modify the rhombohedral morphology of calcite crystals, and the higher one (cmax) provoked a drastic change from the rhombohedral morphology of the calcite particles. Concentrations higher than cmax did not provoke any substantial change in morphologies. Lower or higher concentrations than those above did not have a significant morphological effect on calcite crystals or induced a significant inhibition of precipitation, respectively. Use of an intermediate concentration cint, with cmin < cint < cmax, showed the copresence of both populations of crystals observed using concentrations cmin and cmax or mixed morphologies (see Figure S5, Supporting Information). A first set of samples was analyzed just after the precipitation process (i.e., diffusion of CO2 and NH3 vapors) and stopped at the end of 4 days. A second set of samples was left in the mother solution for an additional 2 weeks, stopping NH3/CO2 gases diffusion, and then analyzed. During this period the solution was no longer fed with carbonate ions and the degree of saturation was reduced, even if the experimental set up does not allow one to evaluate it. In this second set of samples a

Figure 2. Crossed polarizer optical micrographs of calcium carbonate precipitated in the presence of CP1−3. CP1, CP2, and CP3 indicate, respectively, CP1, CP2, and CP3 and the subscripts cmin (CP1, 0.05 mg/mL; CP2, 0.078 mg/mL; CP3, 0.072 mg/mL) and cmax (CP1, 2.5 mg/mL; CP2, 3.9 mg/mL; CP3, 3.6 mg/mL) the additive concentrations. In the insets the corresponding optical micrographs are shown. Scale bars correspond to 100 μm.

In all cases the presence of cmin of CP yielded rhombohedrallike crystals. A different degree of aggregation was observed as a function of the CP used. CP3 favored aggregation of the rhombohedral-like crystals more than CP1 or CP2. Moreover, the average size of the crystals grown in the presence of CP1 was higher than those precipitated in the presence of CP2 or CP3. A different scenario appeared when the cmax of the CPs was used: crystals strongly aggregated. In the presence of CP1 or CP3 they formed also short chains of rhombohedral-like crystals, while in the presence of CP2 spherulites appeared. They exhibited a Maltese cross pattern, which was indicative of radial growth and symmetry. The average size of crystalline aggregates, or spherulites, increased with cmax of CPs, while the density of crystallization decreased with respect to cmin of CPs (see Figures 1 and S5, Supporting Information). FTIR spectra (Figure 3) of the precipitates showed only the typical bands of calcite at 1420 (ν3), 875 (ν2), and 713 cm−1 1941


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Figure 4. X-ray powder diffraction patterns of calcium carbonate crystallized in the presence and absence of CP1−3. (Ctrl) Pure calcite. CP1, CP2, and CP3 indicate, respectively, CP1, CP2, and CP3 and the subscripts cmin (CP1, 0.05 mg/mL; CP2, 0.078 mg/mL; CP3, 0.072 mg/mL) and cmax (CP1, 2.5 mg/mL; CP2, 3.9 mg/mL; CP3, 3.6 mg/ mL) the additive concentrations. High background signal in CP1 cmax should be due to the low amount of precipitated sample. Miller indexes of each diffraction peak are indicated, according to the calcite hexagonal unit cell.

Figure 3. FTIR spectra of calcium carbonate crystallized in the presence of CP1−3. (Ctrl) Pure calcite. CP1, CP2, and CP3 indicate, respectively, CP1, CP2, and CP3 and the subscripts cmin (CP1, 0.05 mg/mL; CP2, 0.078 mg/mL; CP3, 0.072 mg/mL) and cmax (CP1, 2.5 mg/mL; CP2, 3.9 mg/mL; CP3, 3.6 mg/mL) the additive concentrations. High background signal in CP1 cmax could be due to the low amount of precipitated sample. Wavenumbers of the main absorption bands are indicated.

(ν4) together with weak bands at 2918 and 2850 cm−1. The latter ones, due to CPs polymers, increased in intensity in the presence of cmax of CPs. It is worth of noting that the ν2/ν4 intensity ratio increases with the concentration of CPs in solution. It has a value of 1.7 in the pure calcite that increases to 1.8 and 2.1, 2.0 and 2.3, and 1.9 and 2.1 at cmin and cmax of the CP1, CP2, and CP3, respectively. Associated with this increase is a small broadening of the ν3 band to higher wavenumbers. X-ray powder diffraction patterns (Figure 4) confirmed the presence of calcite as a unique mineral phase. Indeed, all peaks could be assigned to planes of diffraction of calcite (JCPDF card 47-1743). Relative intensities of the diffraction peaks are in agreement with a random orientation of the crystallites for all samples, unless that for the sample CP1 cmax for which the reflection (110) shows a higher intensity according to a preferential alignment of the crystallographic c axis, [00.1], parallel to the holder surface. Moreover, the absence of a broad diffraction band between 20° and 40° of 2Θ excluded the presence of detectable amounts of amorphous calcium carbonate. When the concentration of CP1 was cmin (0.05 mg/mL) the calcite crystals showed small {hk.0} faces, almost parallel to the crystallographic c axis of calcite, together with the most stable {10.4} faces. These faces increased extension and changed texture, becoming more edged, when the concentration of CP1 was raised to cmax (0.25 mg/mL). The ripening process provoked a widening of the {hk.0} faces on the crystals obtained with cmin of CP1 and on the crystals obtained with cmax of CP1 an etching on the {hk0} faces, which generated many lamellae almost normal to the crystallographic c axis (Figure 5). Figure 6 shows SEM pictures of calcite crystals precipitated in the presence of CP2. The cmin (0.078 mg/mL) of CP2 specifically stabilized the {11.0} faces, which appeared together

Figure 5. SEM pictures of calcite crystals precipitated in the presence of cmin = 0.05 mg/mL or cmax = 2.5 mg/mL of CP1. Subscript r indicates that crystal underwent the ripening process. In the insets are shown details of the CP1-generated crystalline faces. In the presence of cmax of CP1 the majority of crystals grew as aggregates; here, a single crystal is shown for the sake of clearness. These crystals are representative of the entire sample population (see Supporting Information).

with the {10.4} ones. This effect provoked an apparent elongation of the crystal along the c axis. The crystals almost did not show {10.4} faces and strongly aggregated, forming discrete spherulites in which each crystalline unit was well distinguishable when cmax (0.39 mg/mL) of CP2 was used. The crystals obtained in the presence of CP2 were strongly modified by the ripening process. Those grew with cmin of CP2 aggregated, conserved the {11.0} faces, and increased the elongation in the direction of the c axis. On the contrary, the crystalline units making the spherulite separated, generating conical shapes having a smooth surface. 1942


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Figure 6. SEM pictures of calcite crystals precipitated in the presence of cmin = 0.078 mg/mL or cmax = 3.9 mg/mL of CP2. Subscript r indicates that crystals underwent the ripening process. In the insets are shown details of the CP2-generated crystalline faces. These crystals are representative of the entire sample population (see Supporting Information).

In the presence of cmin (0.072 mg/mL) of CP3 the calcitic crystals were not specifically lightly modified, as observed in the presence of cmin of CP1. Calcite particles appeared either as cylindrical shapes spherical capped or as aggregates of the rhombohedral crystals observed in the presence of cmin of CP3, when cmax (0.32 mg/mL) of CP3 was present in solution. Ripening of these crystalline structures provoked the overgrowth of an enveloping layer made of small (∼500 nm) rhombohedral calcite crystals, at which was associated a light smoothing of the surface of the underlying aggregates (Figure 7). The amount of CP1−3 entrapped and adsorbed in the calcite particles was evaluated by thermogravimetric analyses (TGA). In the particles obtained in the presence of cmin of CP1−3 the content of CP was around 0.5% (w/w). A content of 1.5% (w/ w), 1.9% (w/w), and 1.3% (w/w) of CP1, CP2, and CP3, respectively, was measured in the particles precipitated in the presence of cmax. In these samples a weight loss was observed as well just prior to pyrolysis of CP1−3; this made difficult an accurate measure. The decomposition temperature of the calcite particles was not influenced by the presence of entrapped CP1−3 and always started at about 600 °C (Figure S6, Supporting Information).

Figure 7. SEM pictures of calcite crystals precipitated in the presence of cmin = 0.072 mg/mL or cmax = 3.2 mg/mL of CP3. Subscript r indicates that crystal underwent the ripening process. In the insets are shown details of the CP3-generated crystalline faces. In the presence of cmax of CP3 the particles grew as spherical aggregates of the rhombohedral crystals (CP3cmax) or as cylindrical shapes sphericalcapped aggregates (CP3acmax). These crystals are representative of the entire sample population (see Supporting Information).

low cost.12 The mechanism by which DHBCs can control the morphology and association of calcium carbonate crystals has been deeply investigated,27−29 while scant information is available for CPs. The presence of DHBCs typically favors formation of precursor ACC particles, which subsequently transform into either vaterite or calcite primary particles.27−29 Temporary stabilization of these primary units by interaction with the DHBCs retards further growth such that aggregation of these particles proceeds more rapidly than growth of individual particles. This process evolves in formation of mesocrystals or polycrystalline aggregates. Following this synthetic route DHBCs bearing side groups, such as carboxylates, sulfonates, and phosphates,20 have been shown to mediate formation of calcite particles with morphologies including hollow spheres,21 spherules,22 and dumbbells.23 In CPs the capability of the polyelectrolytic backbone chain to interact with the mineral phase is regulated by the presence of the grafted chains. The latter influence the aggregation and eventually the conformation of the polyelectrolytic chain and the speciation of ionizable functional groups. Here, a reduction of the HR of the CP1−3 as a function of the fraction of ionized carboxylic groups (i.e., increase of pH) was observed. This can be attributed to good solvent effects, which lower the apparent value of HR.45 Moreover, this may also suggest that the CP1−3 partially disaggregate once charged, probably due to the repulsion among carboxylate groups and ether functions. The interchain aggregates should form via the hydrogen bonding

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DISCUSSION Solution additives can deeply modify the crystal morphology.39−43 According to the classical crystallization mechanism new faces can appear in the crystal as a consequence of selective additive adsorption on otherwise not energetically favored crystalline faces and/or additive inhibiting effect in the step growth.44 In the nonclassical crystallization mechanism the final morphology of the crystals is dictated by the principles of surface area minimization of nanoparticles, the additives having a role in the stabilization and aggregation of nanoparticles.24−27 While among calcium carbonate crystal shape modifiers DHBCs have been widely and successfully used,19−29 CPs, their composition analogous, have received far less attention.6 This is despite their wide application as cement superplasticizers and 1943


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Table 4. Mineralogical and Structural Features of the Calcite Particles Precipitated in the Presence CP1−3 code CP1 CP2 CP3

conc. (mg/mL)

shape

morphology {hkl}

0.025 0.5 0.078 0.39 0.072 0.32

a

{hk.4} {hk.0} {10.4} {hk.0} {10.4} {11.0} {10.4} {11.0} {10.4} {hk.0} {10.4} {hk.0}

single particles and aggregates aggregates single particles spherulites single particles and aggregates aggregatesb

average size (μm)

CP contentc % (w/w)

ν2/ν4 intensity ratio

± ± ± ± ± ±

∼0.5 ∼1.5 ∼0.5 ∼1.9 ∼0.5 ∼1.3

1.8 2.1 2.0 2.3 1.9 2.1

40 30 25 40 25 40

5 5 5 5 5 5

a These particles had sizes and morphologies that were consistent with single crystals of calcite, and examination between crossed polars in an optical microscope demonstrated uniform extinction as is characteristic of single crystals. bThese aggregates are nonoriented and polycrystalline. cThe low content of CP1−3, as well the presence of bounded water, in the composite CP1−3/calcite particles did not allow an accurate measure.

CP1−3 interaction with calcium carbonate particles produces an inhibition on the precipitation of calcium carbonate. This requires that an inhibition of particle nucleation and/or growth was present. Since in the precipitation system there is a continuous feeding of NH3/CO2 gases in solution, the carbonate concentration (i.e., the supersaturation) increases with the time, unless a precipitation event occurs. Thus, in the presence of high concentrations of CP1−3, in this particular system, precipitation should occur under conditions of high calcium carbonate supersaturation, as already observed in the presence of DHBCs.25−28 Calcite crystals grown in the presence of cmin of CP1, having a high degree of grafting, or CP3, grafted with long chains of MPEG, showed only a light modification with respect to the perfect rhombohedral morphology. On the contrary, the low grafting of CP2 ensures a specific interaction between the carboxylate groups of the PAA chain and the {11.0} crystalline planes of calcite. Calcite crystals of similar morphology were obtained also in the presence of poly(4-styrenesulfonate-comaleic acid).28,29 In analyzing the CP1−3 behavior as a calcite morphology modifier it is important to note that PAA chains gave nonspecific interactions with calcite crystals on several crystalline planes, generating rounded shapes (Figures S3 and S4, Supporting Information).6 Thus, the interacting capability of the carboxylate groups with calcite crystal is reduced and modulated by the MPEG teeth along the PAA chain. Studies with aspartic polypeptides of different length have demonstrated that there is a threshold number of carboxylate groups to give a specific interaction on calcite crystals.49 The ripening process of these crystals did not have a strong effect of their morphology and aggregation, in agreement with the low content of entrapped CP1−3. Moreover, different from what was observed in the presence of cmax of CP1−3, the {10.4} faces appeared completely flat. All these observations can be justified according to a classical mechanism of precipitation.27 A different calcite precipitation scenario was observed when high concentrations (cmax) of CP1−3 and probably high condition of supersaturation were used. In these conditions the CP1−3 capability of coverage and stabilization of calcium carbonate particles is increased. This effect was more evident for CP1 and CP2 than CP3. Here, according to the studies reported using DHBCs, a nonclassical mechanism of crystallization could be invoked. This supposition is supported by the following observations: (i) CP1−3/calcite composites show a higher atomic disorder (higher ν2/ν4 in the FTIR spectra) with respect to pure calcite crystals; this could be a clue of precipitation through an amorphous intermediate;50 (ii) the crystal surface appears rough and the ripening process had a strong effect on the morphology of the crystals; (iii) the morphologies of these calcite particles were already observed

between the carboxylic group on PAA chains and the ether oxygen on MPEG chains, as already observed in a similar polymer.11 The light increase of pKa values of the CP1−3 polymers with respect to the PAA chain could be a consequence of the decrease of number of carboxylate groups along the chain due to the grafting process.46 However, the hydrogen bond formation, which makes less favorable the ionization of the carboxylic groups, should also play an important role as well the reduced capability of carboxylate groups solvation. FTIR data from CP1−3 aggregates formed at different pHs support the hydrogen-bonding assumption. Indeed, in acidic conditions, where strong aggregation occurs, the carboxylic groups stretching band trends shift to higher wavenumbers and the OH bending band tends to increase in intensity. Establishment of these hydrogen-bond cross-linkages is constrained by steric effects, which could balance between inter- and intrachain interactions. The former seem favored by a low degree of grafting and the presence of long MPEG chains, as occurs in CP3. The presence of calcium ions, which interact with the carboxylate groups, favors formation of salt bridges between PAA chains of the CP1−3 with a consequent significant increase of the HR (Table 2). These interactions, which easily occur among the PAA chains,47,48 are more difficult to establish among the CP1−3 due to the steric hindrance given by the MPEG-grafted chains. Accordingly, in the presence of calcium ions the HR increased more for PAA and CP3 than for CP1 and CP2, where a higher percentage of grafting is present. This structural reorganization seems to reduce the strength of the hydrogen-bond interaction, as suggested by the small shift of the stretching energy of the carboxylic groups. Table 4 summarizes the capability of CP1−3 to control the shape and aggregation of calcite particles. This capability implies the establishment of interactions between the CP carboxylate groups and the crystalline planes of calcite according to the classical mechanism of crystallization; following the nonclassical mechanism a CP1−3-mediated stabilization of calcium carbonate nanoparticles should occur. The two components of the CP1−3, the PAA and the MPEG polymers, act on the calcite morphology as a strong modifier and as a noninteracting additive (Figures S3 and S4, Supporting Information), respectively. Moreover, in the presence of PAA, which strongly aggregates in the presence of calcium ions, an association of the calcite particles is observed, while calcite particles remain as single units even in the presence of a high concentration of MPEGs, which do not associate in the presence of calcium ions. Thus, MPEGs do not interact with calcium carbonate particles and glide them, while on the contrary PAA interacts with them and links them. This dichotomy is present in CP1−3, as occurs in many DHBC. 1944


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CONCLUSIONS In summary, the presented results demonstrate that the interaction of calcite crystals with PAA chain grafted in different extent with hydrophilic MPEG chains can generate complex CP/calcite composites. CP1−3 behave similarly to double hydrophilic block copolymers, their compositional analogues. The calcite precipitation processes seem addressed to the classical or nonclassical mechanism by concentration and structure of CP1−3. In the presence of CP2 the nonclassical one seems favored. CP1 switches from the classical mechanism to the nonclassical one, moving from conditions of low to high calcium carbonate supersaturation. CP3 seems to favor the classical mechanism of precipitation. MPEG grafting controls also the CP1−3 ionization, aggregation, and capability to interact specifically with calcite crystalline planes. A specific molecular recognition onto crystalline planes can be achieved only when the optimal degree of grafting is present in the polyelectrolitic chain and the length of the grafted chains does not shield the ionizable functional groups. In conclusion, this study has important implications not only in the understanding of the complex chemical processes associated with concrete superplasticizers but also in the study of the mineralization processes by organisms, where biological comb polyelectrolytes, the acidic glycoproteins, control formation of calcitic structures.51−53

for calcite mesocrystals precipitated in the presence of DHBCs.19−30 The latter formed by assembly of the calcite nanoparticles, which is governed by the DHBC low-interacting blocks. A similar role should be associated to the MPEG teeth of the CP1−3. However, since the MPEG chains do not interact with calcite crystals but mediate the interaction among CP1−3 molecules (see DLS and FTIR data), the presence of aggregates of CP1−3 molecules, exposing particle bridging carboxylate groups, onto the calcite nanoparticles surfaces is plausible. Indeed, mineral nanoparticles have a strong tendency to aggregate to reduce the whole surface energy. In supposed conditions of low calcium carbonate supersaturation (cmin), CP2 has the highest capability to interact with calcite crystals and thus to associate calcite nanoparticles. This brings about formation of big spherulitic aggregates, similar to those observed in the presence of poly(ethylene glycol)-blockpoly(methacrylic acid).22 Upon ripening, the CP2/calcite spherulites undergo cleavage of the constituting units, according to the presence on their surface of linking assemblies of CP2. CP1, which in conditions of high calcium carbonate supersaturation has a less specific and a lower capability of interaction with calcite than CP2, does not change the overall morphology and association of the crystals. Its embedding into calcite crystals appears evident from a strong etching on the {hk.0} faces after ripening experiments. These observations indicate that the particle regions in which CP is entrapped are less stable (i.e., more soluble) and thus more affected by the ripening process. This implies that the CP1 and CP2 during the growing process of crystals, or spherulites, are not homogenously entrapped but mainly located on the {hk.0} planes or among the crystalline units forming the spherulites, respectively. This not homogeneous distribution of additives was also observed in poly(4-styrenesulfonate)/calcite composites.30 CP3 molecules are exposing long MPEG teeth; these chains shield the carboxylate groups and reduce their capability to interact with the calcite crystals. As consequence, the amount of polymeric molecules entrapped into the crystals is reduced and the ripening experiments showed only a superficial low etching of calcite crystals, at which was associated a reprecipitation on their surface of not oriented calcite crystals. These results show that CP1−3 concentration, which influences the calcium carbonate supersaturation at which the precipitation occurs, and structure, which controls the capability of molecular assembly and interaction with calcite crystals, are crucial parameters to govern precipitation of calcite particles having different morphologies. In similar conditions of supersaturation the degree and kind of hydrophilic teeth grafting along the polyelectrolytic chain seem to address the precipitation processes by classical or nonclassical mechanisms. This observation has strong implications not only in the capability of CPs to act as cement superplasticizers but also in the evaluation of the role and function of acidic glycoproteins in control of the precipitation of calcium carbonate in calcifying organisms.51−53 Albeck et al. demonstrated that the capability of glycosylated acidic proteins extracted from sea urchin spines and mollusk shells to specifically modify the morphology of calcite is changed when these macromolecules are deglycosylated.51 This work may suggest that the organisms could modulate the action and role of glycosylated acidic proteins by controlling the glycosylation process.

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ASSOCIATED CONTENT

S Supporting Information *

Titrations curves of CP1−3; FTIR spectra of CP1−3; OM and SEM pictures of calcite crystals precipitated in the presence of PAA and MPEG, the CP1−3 constituents; SEM pictures of the CP1−3/calcite crystals obtained using increasing concentration of CP1−3; TGA profiles of CP1−3/calcite crystals. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 0039 051 2099484. Fax:0039 051 2099456. E-mail: [email protected]. Author Contributions

D.M., S.F., and G.F. did the experiments. G.F., P.G., M.G., and E.T. designed the experiments. All authors contributed equally to the discussion and writing of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS G.F. and S.F. thank the Consorzio Interuniversitario di Ricerca della Chimica dei Metalli nei Sistemi Biologici (CIRC MSB) for support.

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ABBREVIATIONS CP: comb polyelectrolyte; DHBCs: double hydrophilic block copolymers; MPEG: methoxy poly(ethylene glycol); PAA: poly(acrylic acid) ; GPC: gel permeation chromatograph; HR: hydrodynamic radius; DLS: dynamic light scattering; FTIR: Fourier transform infrared spectroscopy; XRD: X-ray powder diffraction; SEM: scanning electron microscopy; OM: optical microscopy 1945


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(21) Marentette, J. M.; Norwig, J.; Stockelmann, E.; Meyer, W. H.; Wegner, G. Crystallization of CaCO3 in the presence of PEO-blockPMAA copolymers. Adv. Mater. 1997, 9, 647−651. (22) Yu, S. H.; Cölfen, H.; Hartmann, J.; Antonietti, M. Biomimetic Crystallization of Calcium Carbonate Spherules with Controlled Surface Structures and Sizes by Double-Hydrophylic Block Copolymers. Adv. Funct. Mater. 2002, 12, 541−545. (23) Cö lfen, H.; Qi, L. A Systematic Examination of the Morphogenesis of Calcium Carbonate in the Presence of a DoubleHydrophilic Block Copolymer. Chem.Eur. J. 2001, 7, 106−116. (24) Cölfen, H.; Mann, S. Higher-Order Organization by Mesoscale Self-Assembly and Transformation of Hybrid Nanostructures. Angew. Chem., Int. Ed. 2003, 42, 2350−2365. (25) Wang, T.; Antonietti, M.; Cölfen, H. Calcite Mesocrystals: “Morphing” Crystals by a Polyelectrolyte. Chem.Eur. J. 2006, 12, 5722−5730. (26) Wang, T.; Cölfen, H.; Antonietti, M. Nonclassical Crystallization: Mesocrystals and Morphology Change of CaCO3 Crystals in the Presence of a Polyelectrolyte Additive. J. Am. Chem. Soc. 2005, 127, 3246−3247. (27) Kulak, A. N.; Iddon, P.; Li, Y.; Armes, S. P.; Cölfen, H.; Paris, O.; Wilson, R. M.; Meldrum, F. C. Continuous Structural Evolution of Calcium Carbonate Particles: A Unifying Model of CopolymerMediated Crystallization. J. Am. Chem. Soc. 2007, 129, 3729−3736. (28) Song, R.-Q.; Xu, A.-W.; Antonietti, M.; Cölfen, H. Calcite Crystals with Platonic Shapes and Minimal Surfaces. Angew. Chem., Int. Ed. 2009, 48, 395−399. (29) Song, R.-Q.; Cölfen, H.; Xu, A.-W.; Hartmann, J.; Antonietti, M. Polyelectrolyte-Directed Nanoparticle Aggregation: Systematic Morphogenesis of Calcium Carbonate by Nonclassical Crystallization. ACS Nano 2009, 3, 1966−1978. (30) Schenk, A. S.; Zlotnikov, I.; Pokroy, B.; Gierlinger, N.; Masic, A.; Zaslansky, P.; Fitch, A. N.; Paris, O.; Metzger, T. H.; Cölfen, H.; Fratzl, P.; Aichmayer, B. Hierarchical Calcite Crystals with Occlusions of a Simple Polyelectrolyte Mimic Complex Biomineral Structures. Adv. Funct. Mater. 2012, 22, 4668−4676. (31) Antonietti, M.; Breulmann, M.; Göltner, C.; Cölfen, H.; Wong, K. K.; Walsh, D.; Mann, S. Inorganic/Organic Mesostructures with Complex Architectures: Precipitation of Calcium Phosphate in the Presence of Double-Hydrophilic Block Copolymers. Chem.Eur. J. 1998, 4, 2493−2500. (32) Qi, L.; Cölfen, H.; Antonietti, M. Crystal Design of Barium Sulfate using Double-Hydrophilic Block Copolymers. Angew. Chem., Int. Ed. 2000, 39, 604−607. (33) Qi, L.; Cölfen, H.; Antonietti, M. Control of Barite morphology by double-hydrophilic block copolymers. Chem. Mater. 2000, 12, 2392−2403. (34) Ö ner, M.; Norwig, J.; Meyer, W. H.; Wegner, G. Control of ZnO Crystallization by a PEO-b-PMAA Diblock Copolymer. Chem. Mater. 1998, 10, 460−463. (35) Turesson, M.; Labbez, C.; Nonat, A. Calcium Mediated Polyelectrolyte Adsorption on Like-Charged Surfaces. Langmuir 2011, 27, 13572−13581. (36) de Reese, J.; Plank, J. Adsorption of Polyelectrolytes on Calcium Carbonate − Which Thermodynamic Parameters are Driving This Process? J. Am. Ceram. Soc. 2011, 94, 3515−3522. (37) Maltesh, C.; Somasundaran, P.; Kulkarni, R. A.; Gundiah, S. Polymer-polymer complexation in dilute aqueous solutions: poly(acrylic acid)-poly(ethylene oxide) and poly(acrylic acid)-poly(vinylpyrrolidone). Langmuir 1991, 7, 2108−2111. (38) Xie, A. J.; Zhang, C. Y.; Shen, Y. H.; Qiu, L. G.; Xia, P. P.; Hu, Z. Y. Morphologies of calcium carbonate crystallites grown from aqueous solutions containing polyethylene glycol. Cryst. Res. Technol. 2006, 41, 967−971. (39) Falini, G.; Fermani, S.; Ripamonti, A. Crystallization of Calcium Carbonate Salts into Beta-Chitin Scaffold. J. Inorg. Biochem. 2002, 91, 475−480.

REFERENCES

(1) Ballauff, M.; Borisov, O. V. Polyelectrolyte brushes. Curr. Opin. Colloid Interface Sci. 2006, 11, 316−323. (2) Tobori, N.; Amari, T. Rheological behavior of highly concentrated aqueous calcium carbonate suspensions in the presence of polyelectrolytes. Colloids Surf. A 2003, 215, 163−171. (3) Claesson, P. M.; Poptoshev, E.; Blomberg, E.; Dedinaite, A. Polyelectrolyte-mediated surface interactions. Adv. Colloid Interface Sci. 2005, 114, 173−187. (4) Papagiannopoulos, A.; Fernyhough, C. M.; Waigh, T. A.; Radulescu, A. Scattering Study of the Structure of Polystyrene Sulfonate Comb Polyelectrolytes in Solution. Macromol. Chem. Phys. 2008, 209, 2475−2486. (5) Wegner, G.; Baun, P.; Muller, M.; Norwig, J.; Landfester, K. Polymers designed to control nucleation and growth of inorganic crystals from aqueous media. Macromol. Symp. 2001, 175, 349−356. (6) Falini, G.; Manara, S.; Roveri, N.; Goisis, M.; Manganelli, G.; Cassar, L. Crystallization of Calcium Carbonate in the Presence of Polymeric Additives Relevant for the Cement Industries. CrystEngComm 2007, 9, 1162−1170. (7) Falini, G.; Fermani, S.; M. Goisis, M.; Manganelli, G. G. Calcite Morphology and Aggregation in the Presence of Comb-like Polymers Adsorbed on Cement Particles. Cryst. Growth Des. 2009, 9, 2240− 2247. (8) Taubert, A.; Kubel, C.; Martin, D. C. Polymer-Induced Microstructure Variation in Zinc Oxide Crystals Precipitated from Aqueous Solution. J. Phys. Chem. B 2003, 107, 2660−2663. (9) Zhong, S.; Cui, H. G.; Chen, Z. Y.; Wooley, K. L.; Pochan, D. J. Helix self-assembly through the coiling of cylindrical micelles. Soft Matter 2008, 4, 90−93. (10) Xu, Y. Y.; Bolisetty, S.; Drechsler, M.; Fang, B.; Yuan, J. Y.; Harnau, L.; Ballauff, M.; Muller, A. H. E. Manipulating cylindrical polyelectrolyte brushes on the nanoscale by counterions: collapse transition to helical structures. Soft Matter 2009, 5, 379−384. (11) Hao, J.; Yuan, G.; He, W.; Cheng, H.; Han, C. C. Interchain Hydrogen-Bonding-Induced Association of Poly(acrylic acid)-graftpoly(ethylene oxide) in Water. Macromolecules 2010, 43, 2002−2008. (12) Malhotra, V. Superplasticizers and Other Chemical Admixtures in Concrete; American Concrete Institute: Fragminton Hills, MI, Ontario, Canada, 2000. (13) Winnefeld, F.; Becker, S.; Pakusch, J.; Goetz, T. Effects of the molecular architecture of comb-shaped superplasticizers on their performance in cementitious systems. Cem. Concr. Comp. 2007, 29, 251−262. (14) Labbez, C.; Jönsson, B.; Pochard, I.; Nonat, A.; Cabane, B. Surface Charge Density and Electrokinetic Potential of Highly Charged Minerals: Experiments and Monte Carlo Simulations on Calcium Silicate Hydrate. J. Phys. Chem. B 2006, 110, 9219−9230. (15) Flatt, J. F.; Schober, I.; Raphael, E.; Plassard, C.; Lesniewska, E. Conformation of Adsorbed Comb Copolymer Dispersants. Langmuir 2009, 25, 845−855. (16) Whitby, C. P.; Scales, P. J.; Grieser, F.; Healy, T. W.; Kirby, G.; Lewis, J. A.; Zukoski, C. F. PAA/PEO comb polymer effects on rheological properties and interparticle forces in aqueous silica suspensions. J. Colloid Interface Sci. 2003, 262, 274−281. (17) Jönsson, B.; Nonat, A.; Labbez, C.; Cabane, B.; Wennerström, H. Controlling the cohesion of cement paste. Langmuir 2005, 21, 9211−9221. (18) Sedlak, M.; Antonietti, M.; Cölfen, H. Synthesis of a new class of double-hydrophilic block copolymers with calcium binding capacity as builders and for biomimetic structure control of minerals. Macromol. Chem. Phys. 1998, 199, 247−254. (19) Cölfen, H. Double-hydrophilic block copolymers: Synthesis and Application as Novel Surfactants and Crystal Growth Modifiers. Macromol. Rapid Commun. 2001, 22, 219−252. (20) Cölfen, H.; Antonietti, M. Crystal Design of Calcium Carbonate Microparticles Using Double-Hydrophilic Block Copolymers. Langmuir 1998, 14, 582−589. 1946


Langmuir

Article

(40) Sommerdijk, N. A. J.; de With, G. Biomimetic CaCO3 Mineralization Using Designer Molecules and Interfaces. Chem. Rev. 2008, 108, 4499−4550. (41) Meldrum, F. C.; Coelfen, H. Controlling Mineral Morphologies and Structures in Biological and synthetic systems. Chem. Rev. 2008, 108, 4332−4342. (42) Njegiä Džakula, B.; Brécevic, L.; Falini, G.; Kralj, D. Calcite crystal growth kinetics in the presence of charged synthetic polypeptides. Cryst. Growth Des. 2009, 9, 2425−2434. (43) Donners, J.; Nolte, R. J. M.; Sommerdijk, N. A. J. ShapePersistent Polymeric Crystallization Template for CaCO3. J. Am. Chem. Soc. 2002, 124, 9700−9701. (44) Addadi, L.; Weiner, S. Control and Design Principles in Biological Mineralization. Angew. Chem., Int. Ed. 1992, 31, 153−169. (45) W. Mandema, W.; Zeldenrust, H. Diffusion of polystyrene in tetrahydrofuran. Polymer 1977, 835−839. (46) Protein Identification and Analysis Tools on the ExPASy Server. In The Proteomics Protocols Handbook; Gasteiger, E., Hoogland, C., Gattiker, A., Duvaud, S., Wilkins, M. R., Appel, R. D., Bairoch, A., Walker, J. M., Eds.; Humana Press: Totowa, NJ, 2005; pp 571−607. (47) Lages, S.; Michels, R.; Huber, K. Coil-Collapse and CoilAggregation due to the Interaction of Cu2+ and Ca2+ Ions with Anionic Polyacylate Chains in Dilute Solution. Macromolecules 2010, 43, 3027−3035. (48) Liu, J.; Pancera, S.; Boyko, V.; Gummel, J.; Nayuk, R.; Huber, K. Impact of Sodium Polyacrylate on the Amorphous Calcium Carbonate Formation from Supersaturated Solution. Langmuir 2012, 28, 3593− 3605. (49) Elhadj, S.; Salter, A.; Wierzbicki, A.; De Yoreo, J. J.; Han, N.; Dove, P. M. Polyaspartate chain length as a stereochemical switch for control of calcite growth and morphology. Cryst. Growth Des. 2006, 6, 197−201. (50) Beniash, E.; Aizenberg, J.; Addadi, L.; Weiner, S. Amorphous calcium carbonate transforms into calcite during sea urchin larval spicule growth. Proc. R. Soc. London B 1997, 264, 461−465. (51) Albeck, S.; Weiner, S.; L. Addadi, L. Polysaccharides of intracrystalline glycoproteins modulate calcite crystal growth in vitro. Chem.Eur. J. 1996, 2, 278−284. (52) Arias, J. L.; Fernandez, M. S. Polysaccharides and Proteoglycans in Calcium Carbonate-based Biomineralization. Chem. Rev. 2008, 108, 4475−4482. (53) Goffredo, S.; Vergni, P.; Reggi, M.; Caroselli, E.; Levi, O.; Dubinsky, Z.; Falini, G. The organic matrix influences precipitation of skeletal calcium carbonate in the Mediterranean coral (Balanophyllia europaea). PloS ONE 2011, 6, e22338.

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Shaping Calcite Crystals by Means of Comb Polyelectrolytes Having

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