Size- and Shape-Controlled Synthesis of Calcium Silicate Particles

Article Cite This: Langmuir XXXX, XXX, XXX−XXX

pubs.acs.org/Langmuir

Size- and Shape-Controlled Synthesis of Calcium Silicate Particles Enables Self-Assembly and Enhanced Mechanical and Durability Properties Rouzbeh Shahsavari*,†,‡,§,∥ and Sung Hoon Hwang‡ Department of Civil and Environmental Engineering, ‡Department of Materials Science and NanoEngineering, and §The Smalley-Curl Institute, Rice University, Houston, Texas 77005, United States ∥ C-Crete Technologies LLC, 13000 Murphy Road, Suite 102, Houston, Texas 77477, United States Langmuir Downloaded from pubs.acs.org by UNIV OF NEW ENGLAND on 09/25/18. For personal use only.

†

ABSTRACT: Calcium silicate (CS)-based materials are ubiquitous in diverse industries ranging from cementitious materials to bone tissue engineering and drug delivery. As a symbolic example, concrete is the most widely used synthetic material on the planet. This large consumption entails significant negative environmental footprint, which calls for innovative strategies to develop greener concrete with improved properties (to do more with less). Herein, we focus on the physicochemical properties of novel spherical calcium silicate particles with an extremely narrow size distribution and report their promising potential as fundamental building blocks. We demonstrate a scalable size- and shape-controlled synthesis protocol to yield highly spherical CS submicron particles, leading to favorable aggregation mechanisms and thus self-assembly of the bulk ensemble. This optimized kinetics-controlled synthesis is governed by suitable stoichiometric ratio of calcium over silicon, type and concentration of the surfactant, and molar ratio of the alkaline solution. Our extensive nano/micro/macro-characterization results show that the bulk ensemble exhibits many superior properties, such as improved strength, toughness, ductility, and durability, paving the path for bottom-up science-based engineering of concrete.

■

INTRODUCTION Ultrafine particles, tubes, wires, and ribbons have demonstrated a wide range of applications in biology and medicine,1−8 manufacturing and materials,9−14 energy and electronics,15−22 environment,23−28 etc. due to their unique properties. Tuning the size and shape of the abovementioned materials gives rise to further improvement of their physicochemical properties. Although extensive research has been carried out toward exploring the influence of tailoring the size and morphology of the crystalline nanomaterials, such as gold nanoparticles,29−33 metal oxides,34−38 and semiconductor systems,39−42 on their properties, notably fewer studies have been performed on demonstrating the effect of size and shape of poorly crystalline materials, such as calcium silicate (CS)based nano- or submicron materials, on their physicochemical properties.43,44 CS materials are widely applied in industry owing to the large number of beneficial properties, including high strength, thermal stability, and low cost. Among the numerous types of classes within the CS family, calcium−silicate−hydrate (C−S− H), the main product of hydration reaction of Portland cement (PC) is responsible for most of the mechanical properties of the cement paste, such as strength, shrinkage, and durability, and it has been the subject of active research for the past decades.45−48 Here, C stands for CaO, S for SiO2, and H for H2O, and the hyphenated dash refers various combinations of C, S, and H.44 C−S−H has a complex semidisordered layered © XXXX American Chemical Society

nanostructure with variable stoichiometry and morphology as well as defects and porosities,49,50 which make it an excellent example for exploring the effect of size and shape controlling on particles with amorphous structures. In fact, the extensive morphological control of C−S−H particles has been recently attained, thereby proving that the morphology of individual C−S−H particles affects the mechanical properties from the scale of a single, individual particle to bulk ensemble states.44 The different phases of C−S−H are usually differentiated by the structural calcium-to-silicon (Ca/Si) ratio, which is typically assumed to vary from ∼0.6 to ∼2.3, with an average of ∼1.7.51,52 The highest ratio is usually found in neat PC, whereas the lowest ratio is in PC having fly ash or metakaolin.53−57 The Ca/Si ratio is the principal factor responsible for the change in the mean length of the silicate chains and the distance between the layers of C−S−H.58 This ratio is usually calculated by determining the calcium and silicon contents using analytical methods, such as X-ray fluorescence and X-ray photoelectron spectroscopy. With the increasing interests directed toward enhancing the durability of concretes via bottom-up approach, several C−S− H synthesis techniques, including solid-state reaction, sol−gel, hydrothermal, mechanochemical, microwave-assisted, and Received: March 20, 2018 Revised: July 27, 2018

A

DOI: 10.1021/acs.langmuir.8b00917 Langmuir XXXX, XXX, XXX−XXX

Article

Langmuir

Figure 1. (a) SEM image of CS particles, (b) high-resolution TEM image of spherical CS particles, (c) XRD pattern of CS, (d) elemental analysis of CS by scanning electron microscopy energy-dispersive spectroscopy (SEM-EDS), (e) thermogravimetric analysis (TGA) of CS, and (f) Fourier transform infrared (FT-IR) spectrum of CS.

sonochemical methods,59 have been utilized to achieve C−S− H nano- or submicron particles with various forms and shapes, such as nanoneedles,59,60 nanowires,61−63 nanobelts,64,65 and hollow microspheres.66 However, most of the above works have not investigated the extensive durability performance or mechanical properties of the synthesized C−S−H. More importantly, the aforementioned methods are energy-intensive techniques that either require high temperature/pressure and high-cost precursors or result in poor morphology products or reactor corrosion problems. Thus, there is an increasing demand for developing an energy-efficient synthesis technique that utilizes low-cost precursors, resolves the drawbacks of the previous methods, and results in size- and morphologycontrolled C−S−H particles. Using template has been one of the most successful techniques in controlling the shape and adjusting the size of nano- or submicron particles. Templates control the particle growth by providing a constrained environment, by which the shape and size of particles are tuned according to the template. Porous alumina,67,68 polycarbonate membranes,69,70 carbon nanotubes,71,72 and surfactant micelles73,74 are among the common templates utilized for synthesizing size-/shapecontrolled nanoparticles. In the latter template, the surfactant molecules are usually made of a hydrophilic head and a hydrophobic tail that join in a polar solution to form a molecular structure called micelle. The micelles form only if the concentration of the surfactant in the aqueous solution is beyond a certain limit called critical micelle concentration (CMC), which varies depending on the surfactant type. These micelles attract the ions in the solution and grow particles on their outer surface, which in turn attract each other, forming the shape-controlled nanoparticles and assemblies. In the present work, we report a detailed synthesis technique to create size-controlled spherical CS particles, which share similar chemical and compositional properties with the aforesaid C−S−H, exhibiting significant potential for optimized self-assembly. The latter can lead to a bulk structure

with improved ensemble physicochemical properties and durability performance compared to conventional PC. Our group has recently reported the synthesis of porous CS particles using cetyltrimethylammonium bromide (CTAB) as a template and fully leveraged their porous characteristics to load organic sealants and develop a mechanically enhanced, selfhealing composite.75 Building on this work, herein, we demonstrate the promising potential of spherical CS particles as the fundamental building blocks to improve the key mechanical and durability properties of cementitious materials. In addition, we also report the effects of various reaction conditions, including the concentration of catalyst, the initial calcium-to-silicon (Ca/Si) ratio in the starting mixture, and the type of cationic surfactants on the final distribution, size, and properties of the bulk ensemble. Bulk and local properties of the assembled CS particles, including strength, hardness, elastic modulus, durability, etc., are measured by compacting them into the cylindrical pellets using various micro- and macroscale standard test methods.

■

RESULTS Synthesis and Characterization of CS Submicron Particles with a Narrow Size Distribution. The CS particles in the present study were synthesized based on the method described in our recent publication through reacting a calcium salt, i.e., calcium nitrate tetrahydrate (Ca(NO3)2· 4H2O) with over 99% purity, and a soluble silicate, i.e., tetraethyl orthosilicate (Si(OC2H5)4).75 The major deviation from the abovementioned reference is that (i) the particles of this work are “nonporous” due to the omission of the calcination process at 600 °C and (ii) another type of surfactant, dodecyltrimethylammonium bromide (DTAB), was utilized in addition to CTAB. A key parameter in our synthesis is that the concentration of the surfactants in the solution should be beyond the surfactant CMC. To create the surfactant micelles being used as the templates for the formation of spherical CS particles with submicron size, B


Article

Langmuir

Figure 2. (a) Intensity-based size distribution of CS particles acquired using dynamic light scattering (DLS). (b) Nitrogen adsorption/desorption curves for CTAB- and DTAB-based particles.

DTAB and CTAB with the CMCs of ∼14 and ∼1 mM in water were used, respectively.76 DTAB and CTAB when dissolved in aqueous solution with concentrations exceeding their CMCs form spherical surfactant micelles with a diameter of ∼3 nm.77,78 The typical, base-catalyzed formation of mesoporous silica nanoparticles accompanies the hydrolysis of the silica source, thereby generating silicic acid monomers. The as-formed monomers condense to form oligomeric silicate ions, which under alkaline conditions, carry negative charges. Consequently, they are attracted to the positively charged head groups of the CTAB micelles via electrostatic attractions, thereby forming surfactant silicate composites.79 The latter assemble to form nuclei, which grow further and ultimately form spherical particles. In our case, nitrate ions dissociated from calcium nitrate tetrahydrate can adsorb strongly to the CTAB micelles, thereby competing with the silicate ions for adsorption sites.80 This elucidates the considerable induction period observed before precipitation. As the silicate−surfactant assemblies form nuclei and undergo condensation to form spherical particles, calcium ions available in solution coordinate to the silicate ions and ultimately become chemically bonded within the silica network.81 This ultimately precipitates calcium silicate submicron particles with submicron size ranging between 100 and 500 nm. The CS particles were then separated from the solution by vacuum filtration with a paper filter, washed with deionized water or lime solution two times to remove the surfactant, and then dried at 40 °C for 24 h. To ensure that the reaction is complete and the CS particles are entirely precipitated, the samples were stirred for 3 h after the onset of precipitation. The scanning electron microscopy (SEM) images of the CS particles demonstrated the spherical morphology of both CTAB- and DTAB-based particles, confirming that the use of DTAB also induces the formation of individual, spherical particles. Both SEM and transmission electron microscopy (TEM) images indicated that the size of CS particles ranges between 100 and 500 nm (Figure 1a,b). The pattern acquired from the X-ray diffraction (XRD) analysis exhibits a broad hump between 15 and 39°, thereby resembling that of amorphous silica gel and thus, confirming the lack of long-range order within the structure of our glassy CS particles (Figure 1c).82 The energy-dispersive X-ray spectroscopy (EDS) analysis was performed on the bulk CS sample as well as the individual spherical particles, and it was indicated that the particles are

principally composed of calcium, silicon, and oxygen with traces of carbon (Figure 1d). Aluminum peak arises from the SEM specimen stub. Although the starting Ca/Si ratio was ∼1.8, the resulting particles showed different Ca/Si ratios ranging between 0.5 and 1.0 with the average of ∼0.62. The average Ca/Si ratio was acquired by selecting at least five different, relatively flat regions during the SEM analysis, performing SEM-EDS over the desired area on each region and dividing the atomic percent of calcium by the atomic percent of silicon. Considering the severe washing process performed after the synthesis, the presence of calcium ions revealed via the SEMEDS analysis verifies the chemical doping of calcium ions within the structure of silica gel. The TGA−differential scanning calorimetry (DSC) spectra established the presence of adsorbed water molecules via the first peak, located between ambient temperature and about 200 °C, and this is likely due to the incomplete removal of water molecules during the drying process at 40 °C, which is described in the Methods section (Figure 1e).83 The next peaks illustrated within the range of 750−950 °C indicate the weight loss stemming from the removal of carbon dioxide from the nanosized calcite seed particles.84 The FT-IR spectrum showed a steep peak at ∼970 cm−1 emerged due to the Si−O stretching vibrations (Figure 1f). This peak combined with the Si−O−Si bending bands at ∼667 cm−1 confirm the formation of calcium silicate glass phase.85 The bands at 1400−1500 cm−1 further indicate that carbonation has occurred on our particles. Carbonation is the common phenomenon observed in cementitious materials, and it can induce both beneficial and detrimental effects on the mechanical properties depending on specific situations. For example, carbonation can enhance the compressive strength of concretes since the resultant calcium carbonate may decrease the surface porosity.86 On the other hand, another report showed that the presence of sharp carbonation front is detrimental to the mechanical properties.87 The particle size within the range of 100−500 nm is further confirmed by the monomodal, intensity-based size distribution acquired from dynamic light scattering (Figure 2a). The Zaverage value of 329.2 nm, coupled with the low polydispersity index value of 0.039 verifies that the CS particles exhibit narrow size distribution within the range of 100−500 nm. The total pore volumes acquired at the relative pressure (P/P0) of ∼0.95 during the nitrogen adsorption/desorption measurement performed using Brunauer−Emmett−Teller (BET) surface analyzer were 0.062 and 0.051 cm3 g−1 for the C


Article

Langmuir

Figure 3. CS particles synthesized using (a, b) the optimum condition for spherical morphology, where [CTAB] is ∼1 mM, the volume of ammonium hydroxide is 6.7 mL, and the initial Ca/Si ratio is ∼1.8. (c, d) [CTAB] = 1.8 mM. (e, f) [CTAB] = 2.5 mM. (g, h) Volume of ammonium hydroxide 19% higher than the optimum volume. (i, j) Volume of ammonium hydroxide 19% lower than the optimum volume. (k, l) Initial Ca/Si ratio = 1. (m, n) Initial Ca/Si ratio = 2. (o, p) Initial Ca/Si ratio = 4.

carbonate ions arising from dissolved CO2 gases.44 To further inspect the effective factors that control and adjust the CS particles size, morphology, and stoichiometry, we carried out various reactions with different kinetic conditions and molar ratios of the reagents. The effect of reaction temperature, Ca/ Si, surfactant concentration, and surfactant type (CTAB or DTAB) was investigated in this study. The influence of types and concentrations of surfactants on the size and shape of the CS particles was also investigated.32 To probe the role of surfactants in controlling the size and morphology of the CS particles, we investigated the effect of

CTAB-based and DTAB-based particles, respectively. Furthermore, the nitrogen adsorption curves illustrate the greater volume of gas adsorbed on the CTAB-based particles at each relative pressure compared to the DTAB-based particles (Figure 2b). Overall, the results confirm the slightly higher porosity for the CTAB-based particles. In general, the characterization of the synthesized particles revealed that the resultant structures are mostly amorphous CS particles with spherical morphologies and not calcite particles, the formation of which could be promoted by the sufficient amount of calcium ions in solution and also the presence of D


Article

Langmuir

Figure 4. (a) Porosities of the compacted pellets and PC. (b) Maximum compressive strength of the CS pellets and PC. (c) Maximum splitting tensile strength of the compacted pellets and PC. (d) Hardness of the CS pellets and PC control samples. The insets from left to right show the elastic modulus, toughness, and ductility of the samples, respectively. (e) Nanoindentation load−displacement curves for compacted pellets and PC control sample. (f) Displacement vs time. The inset shows the applied load vs time.

morphology (Figure 3c,d). Also, higher concentration of surfactant may favor the formation of surfactant silicate nuclei and restrict the growth. This may have contributed to decreasing the final particle size (Figure 3e,f).88 DTAB and CTAB both have hydrophilic heads that go to the center and hydrophobic hydrocarbon tails that form the outer surface of the micelle and stay in contact with solvent. This results in the formation of spherical micelles and therefore spherical particles. The DTAB micelles are smaller than CTAB because the length of the hydrocarbon chain in CTAB is higher than that in DTAB.89 The length of the hydrocarbon chain in a surfactant has been shown to be a major factor in guiding the CMC and size of the micelles.90 The smaller the micelles, the smaller the resultant CS particles, e.g., using surfactants with micelles size ranging between 1 and 3 nm, we could achieve nanoparticles with diameter 100−200 nm. In addition to the abovementioned important factors, our results also illustrated that the concentration of NH4OH in the

two cationic surfactants, i.e., DTAB and CTAB. Figure 3 shows the SEM images for the CS particles synthesized using various experimental conditions, and each reaction here was scaled down 4 times compared to the method described in Methods. Anionic surfactants do not appear to be appropriate surfactants for this method since cationic or neutral surfactants, which can interact with the silicate ions via electrostatic or hydrogen bonding, respectively, are typically employed for the synthesis of mesoporous silica particles.44 While some oval shape and larger doublet or triplet particles were formed in the presence of CTAB and/or DTAB, the significant proportion of the particles had spherical shape, as illustrated in Figure 3a,b. We found that the interactions of cationic surfactants with a silicate source and the subsequent thermodynamic stabilization are the key reasons for the formation of the well-arranged structures. Although higher concentration of surfactants may enhance the yield of the reaction, the excessive amounts can prompt the formation of particles with nonspherical but elliptical E


Article

Langmuir

made by DTAB and cured for 28 days exhibited ∼30 and ∼105% higher compressive strengths compared to the pellets made by CTAB and the PC control samples, respectively, with similar curing/aging duration. In addition, the tensile splitting test results showed the improved tensile strength and enhanced performance of DTAB-template pellets compared to other compacted pellets, i.e., CTAB-template pellets and PC control samples (Figure 4c). Overall, the results suggest that although the porosities of the pellets are almost comparable, the CS particles made by DTAB are compacted more uniform and efficiently compared to the larger size CTAB-template particles. In addition to this possible mechanistic origin associated with the individual particle size, the exceptional performance of the DTAB-based particles may have arisen from the difference in the intrinsic porosity of individual particles, as revealed by the BET results in Figure 2b. In general, the lower deformation of materials implies the higher stability, strength, and mechanical performance. The localized hardness along with the modulus of elasticity (E) obtained from nanoindentation tests was used as key factors in estimating the deformation in pellets. The nanoindentation results showed that the DTAB-template pellets exhibit lower displacement at the peak load, which indicates the improved hardness of this sample, compared to CTAB-template pellets and PC control samples, resulting in lower material deformation. Figure 4d shows the hardness of compacted pellets after 28 days of curing and aging. The elastic modulus of the samples (E) was also calculated using the load− displacement (l−d) curves. All l−d curves in this figure showed smooth shapes and no pop-in behavior was detected, implying that the compacted samples are hard elastoplastic materials under indentation.94 Among all pellets cured for 28 days, DTAB-template pellets showed the largest elastic modulus, coupled with the higher toughness and ductility (inset of Figure 4d). Evaluation of Durability Properties. All processes affecting the durability of the cement-based materials are reliant on penetration of water or ions into the bulk of the material. For instance, the moisture absorbed by the cementbased materials expands and contracts with the changes in the temperature, and the resulting mechanical actions can initiate cracks and fractures, or the pollutants from acid rain can cause deteriorative chemical reaction with the surface of the material.95 To evaluate the durability of the compacted pellets and compare it to that of the PC control samples, we exposed the 28 days-cured samples to chloride and sulfate ions through three different experiments. Electrical resistivity test was performed, and the results indicated that the DTAB-template pellets have ∼15% higher resistivity compared to CTABtemplate pellets and ∼66% higher electrical resistivity than the PC samples (Figure 5). The electrical resistivity is inversely proportional to the electrical charges passing through the pellets. This implies the high chloride resistance of the CS particles made by DTAB. The chloride diffusivity test also demonstrated the higher refusal rate of DTAB-template pellets against the chloride penetration (Figure 5). The dissolved sulfates in water can attack and destroy a cement-based material that is not properly designed. Sulfates such as sodium sulfate can destroy the cement-based materials by reacting with hydrated compounds in the PC. These chemical reactions can provide sufficient pressure to cause disintegration of the materials. The sulfate expansion tests were performed for the pellets and for the control samples. The

solution influences the morphology, size, and properties of the CS particles such that by increasing the amount of NH4OH, the size of the spheres increased and resulted in a decrease in the yield of individual, spherical particles with the enhanced number of doublets and triplets (Figure 3g,h). This correlates with the previous results based on the Stöber synthesis of monodisperse silica particles, where it was reported that the enhanced concentration of ammonium hydroxide accelerates both hydrolysis and condensation, thereby enhancing the final particle size.91−93 Similarly, decreasing the amount of NH4OH also resulted in the increased number of CS particles with elliptical and irregular morphologies (Figure 3i,j). Overall, we demonstrated that there is an optimum concentration of NH4OH with respect to the other components’ molar ratios, in which the particles had the relevant size and shape. To examine the effect of the initial Ca/Si ratio on the size and morphology of the resultant CS particles, the amount of calcium source, i.e., Ca(NO3)2·4H2O, was varied between 1 and 2, while the amount of silicon source, i.e., Si(OC2H5)4, was kept constant. Other conditions of the reactions, such as surfactant concentration, reaction temperature, etc., were kept almost equal to the original reaction described in the Synthesis Methods section. It was seen that the initial Ca/Si ratio of ∼1.8 was the optimum point for inducing the spherical morphology with narrow size distribution. Lowering the value to ∼1 significantly decreased the yield of spherical CS particles but induced the formation of particles with irregular morphologies (Figure 3k,l). On the other hand, increasing the initial Ca/Si ratio to 2 resulted in the formation of CS particles with larger dimensions and also significantly enhanced the proportions of doublets, triplets, and agglomerates (Figure 3m,n). This is probably because the increased amounts of calcium ions in solution promoted the overgrowth process by facilitating the deposition of silicate ions onto the primary particles and even promoted agglomeration. Further increasing the initial Ca/Si ratio beyond 2 resulted in the formation of similar agglomerates and rendered the morphology of the particles completely irregular. In general, it was found that the kinetic conditions as well as the amount of initial raw materials have significant effects on shape and size of the achieved particles. Overall, we were able to synthesize programmable particles with adjustable size and morphology via controlling the Ca/Si, surfactant concentration, catalyst concentration, and selecting a suitable type of surfactants under specified reaction kinetics. Evaluation of Mechanical Properties. Submicron-sized CS particles, synthesized by using different surfactant types (DTAB or CTAB), were compacted into pellet shapes with comparable porosities by applying a similar compaction pressure of 350 kPa. This compaction pressure was chosen because the porosity of the pellets compacted under the abovementioned pressure was empirically found to be within the same range of the porosity of the control samples with similar dimensions. Figure 4a shows the average porosities of the pellets made by CTAB and DTAB and the control samples (PC) after 3, 7, and 28 days of aging/curing. The average porosity of each pellet was increased by increasing the aging time, while the porosity showed the insignificant difference between the CTAB- and DTAB-based pellets. Figure 4b shows the compressive strength of the pellets with different aging durations. Although the compressive strength of the pellets made by synthesized CS slightly decreased by increasing the aging duration from 3 to 28 days, still the pellets F


Article

Langmuir

evaporation-induced self-assembly of spherical, porous CS particles and the mechanical behavior of their assembled arrays have been recently investigated by our group.106 Herein, we focus on the self-assembly of CS particles with little porosity, suspended in a mixed binary solvent system that contains 50% of water and thus more cost-effective than monosolvent systems comprising only organic solvents. To prepare the suspension of the particles, 0.1 g of synthesized CS particles was mixed with a solvent composed of 10 mL of ethanol and 10 mL of deionized CO2-free water in a 25 mL glass vial. For the first test, the thin glass slide with the dimensions of 5 mm × 50 mm was placed tilted into the glass vial, which was on the hot plate maintained at 80 °C. The elevated temperature not only accelerates the solvent evaporation procedure, but also facilitates the self-assembly by circulating the particles in the solution. The solution was heated at a constant temperature of 80 °C until the solvent was entirely evaporated. Through evaporation of the solvent, the meniscus slowly slides down upon the surface of the tilted glass substrate and results in sedimentation of a layer of the spherical particles on the substrate due to the strong interactions between the particles and the substrate at three-phase contact line, thereby leading to a thin, planar, well-ordered structure of the particles (Figure 6a,b). Subsequent layers of particles may form on the first layer due to the temperature-induced circulation of particles inside the solution, followed by the attractive interparticle interactions that induce free particles to sit on the primary self-assembled layer. Figure 6c shows the SEM image of this multilayer, self-assembled structure of CS submicron particles. To maximize particles packing within a specified area, several experiments with different heating temperatures were carried out and the most condensed selfassembled structure was achieved at 80 °C. For the second test, a similar suspension was prepared in a closed-cap glass vial. One end of a glass capillary tube was immersed ∼5 mm in the suspension and the suspension climbed into the tube by capillary force due to the water

Figure 5. Electrical charge, coefficient of diffusion of chloride, and sulfate expansion of CS pellets and PC control samples.

results were not consistent with the durability results obtained from chloride diffusion and electrical resistivity tests (Figure 5). The samples were initially expanded after exposure to sulfate for 7 days. However, further sulfate exposure of the samples up to 28 days led to the samples shrinkage to their primary dimensions. Studying Self-Assembly of the Spherical Particles. Self-assembly of nano- or submicron-sized materials is a key step toward their integration into a bulk material required for useful applications. Self-assembly of ultrafine particles highly depends on interparticle interactions, particles size, and particle morphology.96,97 Unlike other morphologies of particles, such as cubic, rod-shaped, etc., spherical particles show spontaneous self-assembly only when the dispersity of their size distribution is less than 5%.98 Assembly of spherical particles into wellarranged structures, amenable to practical use, usually requires the initial synthesis of particles, followed by further processing, such as solvent evaporation,99,100 molecular cross-linking,101,102 or template patterning.103−105 Here, we used solvent evaporation technique to assemble the synthesized spherical CS particles first on a microscope glass slide and second inside a capillary tube (internal diameter, 1 mm). A similar

Figure 6. Self-assembly of spherical CS particles. (a, b) Self-assembly on microscope glass slide. (c) SEM image of self-assembled particles on the glass slide. (d, e) Self-assembly on the internal wall of the capillary tube. (f) SEM image of self-assembled particles in the capillary tube. G


Article

Langmuir

this viewpoint, our findings guide toward a completely new manufacturing method of high-performance cementitious materials via a bottom-up approach by assembling the nanoor submicron-sized building blocks with the uniform distribution of size and shape. This will ultimately limit their negative energy and environmental footprints via two ways: (1) increasing the average strength of cement hydrate enables decreasing its structural dimensions and thus its weight and associated CO2 and energy footprints. For example, a concrete with x times improved strength reduces the environmental footprint to 1/x for columns and 1/x0.66 for beams,111 and (2) improving the packing of cement hydrate leads to more concrete durability by preventing deleterious ion penetrations into concrete.112 This higher durability directly translates into less maintenance and replacement cost, thus less impact on energy and environmental footprints.113−115 For instance, a concrete with 2× more durability reduces the concrete manufacturing energy and its associated CO2 emissions to half. Calcium silicate nanomaterials differ from C−S−H in both structural and compositional aspects. Nonetheless, our work confirms the potential of exploiting the former as fundamental building blocks of cementitious materials, where mechanical properties and durability are the key virtues.

surface tension (Figure 6d,e). The solvent evaporation occurred through the other open end of the capillary tube. A shorter capillary tube was placed into the glass vial cap without contacting the suspension for the pressure balance and to expedite the evaporation procedure.107 To facilitate the solvent evaporation, the glass vial was transferred into a furnace set at the constant temperature of 80 °C. Figure 6d shows the schematic diagram for the self-assembly of CS particles inside a capillary. Due to the evaporation of the solvent, the surface of suspension in the tube decreases and an influx of suspension from the bulk toward the meniscus is formed that carries nanoparticles by itself. The CS particles then start to deposit on the internal wall of the tube when the thickness of the solvent meniscus becomes slightly smaller than the size of the particles.107 Figure 6f shows the SEM image of the selfassembled CS particles inside a capillary tube. To prepare the SEM sample, the capillary tube was broken in half and the surface of the sample was coated with a ∼7 nm gold layer by the sputter coating technique. The heating temperature is an important parameter in evaporation-induced self-assembly of monodisperse particles or particles with a narrow size distribution since it determines the evaporation rate of the solvent and the particle layer growth rate.108,109 Without heating, the abovementioned procedures only work for the spherical particles with diameter less than 400 nm because the sedimentation rate of larger particles away from the meniscus is usually higher than the solvent evaporate rate.110 The other important factor is preparing the relevant solvent that facilitates the self-assembly of the particles. Here, an optimized mixture of ethanol and water was prepared because while water provides sufficient surface tension in the meniscus required for particle deposition, ethanol can increase the evaporation rate of the solution and, along with heating, adjust the evaporation rate to the sedimentation rate of larger particles so that they also would be able to move toward the meniscus and deposit on the substrate. The results showed that the thickness of the self-assembled structure via the first technique is larger than that of the structure in the second technique. In the first technique, the suspended particles freely circulate in the solution upon heating and simply approach the glass slide; thus, deposition of the subsequent layers of particles, resulting in the formation of a thicker film, is more feasible. However, in the second technique, only a fraction of particles can climb into the capillary along with the solution. This limits the access and deposition rate of the CS particles onto the internal wall of the capillary tube, thereby leading to the formation of a thin selfassembled structure (Figure 6f). Our results also indicated that the self-assembly is strongly induced by shape and size. It was found that under specified experimental condition, spherical particles do not self-assemble unless they have a very tight size distribution.

■

CONCLUSIONS In summary, this work reports the detailed synthesis and selfassembly of spherical, nonporous CS particles ranging between 100 and 500 nm, which are amenable for facile aggregation and self-assembly to higher-order bulk ensembles with improved mechanical and durability properties. Such a fine control over morphology and size and their associated properties will not only impact the tuning properties of individual CS particles, but will pave the path for de novo concepts and strategies for shape-controlled self-assembly of cementitious microstructures, impacting modern engineering of high-performance concrete materials while mitigating their negative environmental impacts. This bottom-up science-based strategy puts cement and concrete on equal footing with metallic and semiconductor particles in the applications of shape-induced self-assembly mechanisms to create programmable microstructures with ultrahigh performance and low environmental footprints.116−118 Beyond cementitious materials, the innovative concepts, strategies, and techniques of this work can have important implications for other applications of calcium silicates in bone tissue engineering, drug delivery, and refractory materials, and can also impact other complex systems such as ceramics and complex colloids.119,120

■

METHODS

Synthesis Methods. All chemicals, including the calcium source, silicon source, solvent, surfactants, and alkaline solution, were obtained from Sigma-Aldrich. Two separate reactions were performed using two different types of surfactants, one reaction with ∼14 mM of DTAB and another reaction with ∼1 mM of CTAB. In a typical CS synthesis, 1037 mL of deionized CO2-free water was used as the solvent and heated up to 50 °C, and then 26.64 mL of ammonium hydroxide (NH4OH) was added to the solvent as the catalyst. After adding the set amount of the surfactant, the mixture was stirred by a magnetic stirrer for 1 h at 50 °C. The solution was then cooled down to room temperature (RT) and 3.4 mL of Si(OC2H5)4 and 6.7 g of Ca(NO3)2·4H2O were added. The solution was vigorously stirred for 3 h until the CS particles were thoroughly precipitated. Characterizations. Once the CS submicron particles were synthesized, their exact size, morphology, compositions, and micro-

■

DISCUSSION This work suggests that in addition to the chemical composition, the morphology and size of the CS particles, which control the architecture and packing of the microstructure, have a profound influence on the mechanical properties and durability of the bulk materials. The virtue of our controlled synthesis can be understood when considering conventional assembly and growth of cement hydrate, which rely on irregular-shaped and irregular-sized C−S−H particles, leaving multiple levels of porosities in the final structure. From H


Article

Langmuir structure were studied using various advanced characterization techniques. Scanning electron microscopy (SEM) experiments were conducted using an FEI Quanta 400 ESEM FEG instrument. Transmission electron microscopy (TEM) was performed using a JEOL 2100 Field Emission Gun Transmission Electron Microscope. Thermogravimetric analysis (TGA) was carried out on powder CS samples (∼3 mg) to confirm their thermal stability. A Q-600 simultaneous TGA/DSC from TA Instruments at a rate of 20 °C min−1 was used to heat up the CS samples from room temperature (RT) to 1000 °C under argon atmosphere with a flowing rate of 60 mL min−1. Energy-dispersive X-ray spectroscopy (EDS) was used for the elemental analysis of the CS particles and to determine Ca and Si contents. EDS analyses were carried out on a JEOL FEI Quanta 400 ESEM FEG at 20 kV and with a measured beam current of 1 nA. In addition, powder X-ray diffraction (XRD) data were obtained for the identification of the CS phase in the synthesized particles using a Rigaku D/Max-2100 PC powder diffractometer with unfiltered Cu Kα radiation (λ = 1.5406 Å) at 40 kV and 40 mA and a step size of 0.02°. CS particles were characterized by Fourier transform infrared (FT-IR) spectroscopy, which is a useful tool to study the local structure of solids. In this study, the mid-IR spectrum (frequency range, 4000− 400 cm−1) was collected for powdered sample with 128 scans and a resolution of 32 using a Nicolet FT-IR infrared microscope. The total pore volume of CS particles synthesized using CTAB and DTAB was obtained from nitrogen adsorption measurements performed using a Quantachrome Autosorb BET Surface Analyzer. The SEM samples were prepared by depositing a drop of the ethanolic suspension of the particles on an aluminum stub, a silicon wafer, or a glass slide. Prior to depositing the drop on the substrate, the solution was rigorously sonicated for 20 min using an ultrasonic bath (Branson 3800) to obtain a suspension with the perfectly dispersed particles. The solvent in the deposited drop was then evaporated, and the particles remained on the substrate. In the case of using glass slide, the substrate was coated with a thin layer of gold in a CRC-150 sputter coater. TEM samples were prepared by centrifuging the ethanolic suspension in a 15 mL centrifuge vial using an Eppendorf 5804 high-speed centrifuge to provide more diluted suspension and depositing a drop of that onto a carbon-coated copper grid. The solvent was evaporated, and the sample remained on the grid was analyzed. Nanoindentation Test. Using an Anton-Paar nanoindentation tester (NHT2) equipped with the diamond Berkovich tip with a size of ∼50 nm, a grid technique was employed for the indentation tests (100 points in the shape of a 10 × 10 matrix, where each point is 10 μm apart).121,122 A trapezoidal loading−unloading cycle consisting of the three stages, i.e., loading to maximum force, holding for 5 s at the peak load, and unloading periods to evaluate the local surface mechanical characterization data by indenting to depths at the nanoand micrometer scales (Figure 4f). Before testing, the surface of the samples was cleaned with a soft cloth to provide a smooth surface relevant for indentation testing. The nanoindentation was set to the force-controlled mode to apply a maximum force of 2 mN in each indent. Next, from the load−displacement plots of nanoindentation, l−d curves (Figure 4e), we obtained the elastic modulus (E) and hardness (H) using the equations below118−124 E=

0.5πS a

1 − v2

mold into a 50 t hydraulic pressing machine, gradually applying uniaxial pressure (here up to 350 kPa) to the point where the porosity of the compacted samples was within the desired limit, akin to the porosity of naturally hydrated cement. The relevance of comparison of compressed CS or C−S−H particles and naturally set C−S−H is an established subject. It has been demonstrated that the compacted samples of hydrated Portland cement particles exhibit similar Young’s moduli and hardness properties to hardened Portland cement paste.125,126 The compression method was performed using an Instron Dual Column Universal Testing System (model 4500) with a 100 kN load cell to measure the bulk compressive strength, axial deformation, and the elastic modulus of the pellets. After obtaining the load− displacement curves, the stress−strain curves were plotted with respect to the dimensions of the pellets. The maximum strength of the pellets was extracted from stress−strain curve as their compressive strength. The elastic modulus was calculated by measuring the slope of the stress−strain curve in the elastic area of the curve. Due to the brittle nature of cement-based materials, their tensile strength is usually determined by indirect test methods such as the modulus of rupture test or splitting tensile test.127 The splitting test gives the most accurate measurement of the true tensile strength of cement-based materials.128 Thus, we use the splitting test to measure the tensile strength of the CS pellets. The specific jigs were provided that hold the pellets so that the uniaxial compressive force applied to the center lines of the bottom and top surfaces of the pellets causes the tensile stress between the points of contact. Similar to compressive strength, the stress−strain curves were plotted and the maximum tensile strength and elastic modulus of the pellets were measured. Toughness was defined as the amount of energy a material absorbs before failure (representing the work of fracture),44 which is different from the classical “fracture toughness” with the unit of Pa√m. The work of fracture is the area under the stress−strain curve, which is deeply affected by gradual, graceful fracture, whereas the “fracture toughness” does not incorporate this entire process. Ductility is defined as the strain percentage in which the prototypes fail and therefore will be achieved from stress−strain curves. Durability Properties. Besides mechanical properties such as strength, stiffness, etc., durability is another key property that determines the performance of CS pellets. To investigate the durability of the compacted pellets, three most common standard tests of electrical resistivity, chloride diffusivity, and sulfate expansion were performed. For measuring the electrical resistivity, a miniature test setup was designed and built to measure and record the electrical charge passing through the samples every 30 min for 6 h using a multimeter. Passing the current through the saturated samples helps the chloride ions to penetrate more quickly into the samples. The results were recorded and compared to the ASTM standard to explore the durability of our prototypes.129 The side of the pellets was coated with epoxy, and after the epoxy was dried, it was put in a vacuum chamber for 4 h. The pellets were then soaked inside the Ca(OH)2 solution for 24 h to be fully saturated. The calcium hydroxide solution while saturating the pellets hindered leaching of the calcium ions from the soaked pellets into the solution. The sample was then placed in the test setup. The top container of the test device, which was connected to positive electrode, was filled with 0.3 N Na(OH)2 solution, and the bottom container including negative electrode was filled with 3% NaCl solution. A 60 V power supply was used to provide the required current passing through the pellets. The ASTM C1202 standard was precisely followed, and the electrical charges passing through the samples were recorded every 30 min for 6 h using a multimeter. The chloride diffusivity test was performed by exposing the pellets to NaCl solution with 3% concentration in water for 24 h at room temperature and calculating the coefficient of diffusion of chloride. The coefficient of diffusion of chloride into the samples was calculated using the following Fick’s law equation130

, H = lmax /A

where A is the contact area at lmax, S is the slope of the unloading curve, and v is Poisson’s ratio. Bulk Mechanical Properties. To evaluate the performance and mechanical properties of CS particles, the synthesized particles were initially compacted into pellet forms with 30 mm diameter and ∼40 mm heights using a hydraulic pressing machine. The control PC samples were prepared by hydration of Portland cement (PC) with a water-to-cement ratio of 0.4 and by molding in a cylindrical tube with an internal diameter of 30 mm. Compacted pellets were prepared by pouring ∼40 g of the CS particles into a cylindrical mold, placing the I


Article

Langmuir

ÄÅ É| l ÅÅ x ÑÑÑo o ÅÅ ÑÑo − C(x , t ) = C0 + (CS − C0)m 1 erf } o ÅÅÅÇ 2 Dt ÑÑÑÖo o o ~ n

(9) Lee, J. Y.; Buxton, G. A.; Balazs, A. C. Using nanoparticles to create self-healing composites. J. Chem. Phys. 2004, 121, 5531−5540. (10) Puzder, A.; Williamson, A.; Gygi, F.; Galli, G. Self-healing of CdSe nanocrystals: first-principles calculations. Phys. Rev. Lett. 2004, 92, No. 217401. (11) Hau, S. K.; Yip, H.-L.; Baek, N. S.; Zou, J.; O’Malley, K.; Jen, A. K.-Y. Air-stable inverted flexible polymer solar cells using zinc oxide nanoparticles as an electron selective layer. Appl. Phys. Lett. 2008, 92, No. 253301. (12) Zare-Shahabadi, A.; Shokuhfar, A.; Ebrahimi-Nejad, S. Preparation and rheological characterization of asphalt binders reinforced with layered silicate nanoparticles. Constr. Build. Mater. 2010, 24, 1239−1244. (13) Greene, L. E.; Law, M.; Goldberger, J.; Kim, F.; Johnson, J. C.; Zhang, Y.; Saykally, R. J.; Yang, P. Low-temperature wafer-scale production of ZnO nanowire arrays. Angew. Chem., Int. Ed. 2003, 42, 3031−3034. (14) Antunes, M.; Velasco, J. I. Multifunctional polymer foams with carbon nanoparticles. Prog. Polym. Sci. 2014, 39, 486−509. (15) Girão, E. C.; Cruz-Silva, E.; Meunier, V. Electronic transport properties of assembled carbon nanoribbons. ACS Nano 2012, 6, 6483−6491. (16) Lin, J.; Peng, Z.; Xiang, C.; Ruan, G.; Yan, Z.; Natelson, D.; Tour, J. M. Graphene nanoribbon and nanostructured SnO 2 composite anodes for lithium ion batteries. ACS Nano 2013, 7, 6001−6006. (17) Yang, Z.; Liu, M.; Zhang, C.; Tjiu, W. W.; Liu, T.; Peng, H. Carbon nanotubes bridged with graphene nanoribbons and their use in high-efficiency dye-sensitized solar cells. Angew. Chem., Int. Ed. 2013, 52, 3996−3999. (18) Cui, Y.; Lieber, C. M. Functional nanoscale electronic devices assembled using silicon nanowire building blocks. Science 2001, 291, 851−853. (19) Qin, G.; Wu, Q.; Zhao, J.; Ma, Q.; Wang, C. C/LiFePO4/multiwalled carbon nanotube cathode material with enhanced electrochemical performance for lithium-ion batteries. J. Power Sources 2014, 248, 588−595. (20) Tušar, N. N.; Maučec, D.; Rangus, M.; Arčon, I.; Mazaj, M.; Cotman, M.; Pintar, A.; Kaučič, V. Manganese Functionalized Silicate Nanoparticles as a Fenton-Type Catalyst for Water Purification by Advanced Oxidation Processes (AOP). Adv. Funct. Mater. 2012, 22, 820−826. (21) Kind, C.; Feldmann, C.; Quintilla, A.; Ahlswede, E. CitrateCapped Cu 11 In 9 Nanoparticles and Its Use for Thin-Film Manufacturing of CIS Solar Cells. Chem. Mater. 2011, 23, 5269− 5274. (22) Gebresilassie Eshetu, G.; Armand, M.; Scrosati, B.; Passerini, S. Energy storage materials synthesized from ionic liquids. Angew. Chem., Int. Ed. 2014, 53, 13342−13359. (23) Sinha, A. K.; Suzuki, K.; Takahara, M.; Azuma, H.; Nonaka, T.; Fukumoto, K. Mesostructured manganese oxide/gold nanoparticle composites for extensive air purification. Angew. Chem. 2007, 119, 2949−2952. (24) Sreeprasad, T. S.; Maliyekkal, S. M.; Lisha, K.; Pradeep, T. Reduced graphene oxide−metal/metal oxide composites: facile synthesis and application in water purification. J. Hazard. Mater. 2011, 186, 921−931. (25) Cao, L.; Sahu, S.; Anilkumar, P.; Bunker, C. E.; Xu, J.; Fernando, K. S.; Wang, P.; Guliants, E. A.; Tackett, K. N.; Sun, Y.-P. Carbon nanoparticles as visible-light photocatalysts for efficient CO2 conversion and beyond. J. Am. Chem. Soc. 2011, 133, 4754−4757. (26) Zhang, T.; Zhang, X.; Ng, J.; Yang, H.; Liu, J.; Sun, D. D. Fabrication of magnetic cryptomelane-type manganese oxide nanowires for water treatment. Chem. Commun. 2011, 47, 1890−1892. (27) Nowack, B.; Bucheli, T. D. Occurrence, behavior and effects of nanoparticles in the environment. Environ. Pollut. 2007, 150, 5−22. (28) Kim, J.; Van der Bruggen, B. The use of nanoparticles in polymeric and ceramic membrane structures: review of manufacturing

where C(x, t) is the concentration of chloride in a depth of x (m) and time of t (s), C0 is the initial chloride concentration of the sample, CS is the chloride concentration at the surface, and D is the chloride diffusion coefficient. The penetration depth of chloride ion in the pellets was measured by splitting the pellets after exposure to chloride solution and performing elemental analysis in the cross-sectional area using SEM-EDS. The sulfate expansion test was carried out by preparing a sulfate solution with 2 wt % concentration in water and immersing the pellets in the solution for 24 h and calculating the percentage of sample expansion. To calculate the samples expansion, their dimensions before and after the exposure to sulfate were measured. The difference between the dimensions exhibits the expansion percentage of the sample, which is directly related to sulfate ion permeability. Porosity and Bulk Density. The presence of pores in the internal structure of the materials can adversely affect their mechanical properties, including strength, stiffness, durability, etc.131 Thus, to compare various characteristics of different pellets, it is important to create pellets with similar porosities. The bulk density is the mass of the CS particles in pellets over the volume they occupy and affected by the porosity of pellets. We measured the bulk density of the pellets by immersing them in water in accordance with the ASTM C29 standard procedure. The porosity of the pellets was calculated by measuring the dimensions of the pellets and using the density of the ingredients that was determined via a Micromeritics AccuPyc II 1340 helium pycnometer.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Rouzbeh Shahsavari: 0000-0002-6897-881X Notes

The authors declare the following competing financial interest(s): R.S. has a pending patent on this subject.

■

ACKNOWLEDGMENTS This work was supported by the U.S. National Science Foundation grant number 1346506. R.S. thanks the discussions with V. Hejozi at C-Crete Technologies LLC.

■

REFERENCES

(1) Fromen, C. A.; Robbins, G. R.; Shen, T. W.; Kai, M. P.; Ting, J. P. Y.; DeSimone, J. M. Controlled analysis of nanoparticle charge on mucosal and systemic antibody responses following pulmonary immunization. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 488−493. (2) Salata, O. V. Applications of nanoparticles in biology and medicine. J. Nanobiotechnol. 2004, 2, 3. (3) Zhang, L.; Gu, F.; Chan, J.; Wang, A.; Langer, R.; Farokhzad, O. Nanoparticles in medicine: therapeutic applications and developments. Clin. Pharmacol. Ther. 2008, 83, 761−769. (4) Giljohann, D. A.; Seferos, D. S.; Daniel, W. L.; Massich, M. D.; Patel, P. C.; Mirkin, C. A. Gold nanoparticles for biology and medicine. Angew. Chem., Int. Ed. 2010, 49, 3280−3294. (5) Ryu, J. H.; Lee, S.; Son, S.; Kim, S. H.; Leary, J. F.; Choi, K.; Kwon, I. C. Theranostic nanoparticles for future personalized medicine. J. Control. Release 2014, 190, 477−484. (6) Wang, E. C.; Wang, A. Z. Nanoparticles and their applications in cell and molecular biology. Integr. Biol. 2014, 6, 9−26. (7) Louis, C.; Pluchery, O. Gold Nanoparticles for Physics, Chemistry and Biology; World Scientific, 2012. (8) Hainfeld, J. F.; Slatkin, D. N.; Focella, T. M.; Smilowitz, H. M. Gold nanoparticles: a new X-ray contrast agent. Brit. J. Radiol. 2014, 248−253. J


Article

Langmuir

Atomistic modeling and statistical analysis. J. Mech. Phys. Solids 2016, 96, 204−222. (49) Shahsavari, R. Hierarchical Modeling of Structure and Mechanics of Cement Hydrate; MIT, 2011. (50) Shahsavari, R.; Sakhavand, N. Hybrid Cementitious Materials: Nanoscale Modeling and Characterizations. Innovative Development of Advanced Multifunctional Nanocomposites in Civil and Environemntal Engineering; Woodhead Publishing, 2016. (51) Shahsavari, R.; Buehler, M. J.; Pellenq, R. J.-M.; Ulm, F.-J. FirstPrinciples Study of Elastic Constants and Interlayer Interactions of Complex Hydrated Oxides: Case Study of Tobermorite and Jennite. J. Am. Ceram. Soc. 2009, 92, 2323−2330. (52) Shahsavari, R.; Pellenq, R. J. M.; Ulm, F.-J. Empirical Force Fields for Complex Hydrated Calcio-Silicate Layered Materials. Phys. Chem. Chem. Phys. 2011, 13, 1002−1011. (53) Colombet, P., Grimmer, A.-R., Zanni, H., Sozzani, P., Eds.; Nuclear Magnetic Resonance Spectroscopy of Cement-Based Materials; Springer: Berlin, 1996; p 430. (54) Richardson, I. G. The nature of C-S-H in hardened cements. Cem. Concr. Res. 1999, 29, 1131−1147. (55) Richardson, I. G.; Groves, G. W. Microstructure and microanalysis of hardened cement pastes involving ground granulated blast-furnace slag. J. Mater. Sci. 1992, 27, 6204−6212. (56) Richardson, I. G.; Groves, G. W. Models for the composition and structure of calcium silicate hydrate (C-S-H) gel in hardened tricalcium silicate pastes. Cem. Concr. Res. 1992, 22, 1001−1010. (57) Girão, A. V.; Richardson, I. G.; Taylor, R.; Brydson, R. M. D. Composition, morphology and nanostructure of C−S−H in 70% white Portland cement−30% fly ash blends hydrated at 55 °C. Cem. Concr. Res. 2010, 40, 1350−1359. (58) Taylor, H. F. W. Cement Chemistry, 2nd ed.; Thomas Telford Publishing: London, 1997; pp 459. (59) Mehrali, M.; Shirazi, S. F. S.; Baradaran, S.; Mehrali, M.; Metselaar, H. S. C.; Kadri, N. A. B.; Osman, N. A. A. Facile synthesis of calcium silicate hydrate using sodium dodecyl sulfate as a surfactant assisted by ultrasonic irradiation. Ultrason. Sonochem. 2014, 21, 735− 742. (60) Li, Z.; Wang, G.; Yan, C.; Zhang, A. Hydrothermal synthesis of tobermorite nanowires from porcelain stone. Micro Nano Lett. 2014, 9, 536−538. (61) Lin, K.; Chang, J.; Lu, J. Synthesis of wollastonite nanowires via hydrothermal microemulsion methods. Mater. Lett. 2006, 60, 3007− 3010. (62) Pei, L. Z.; Yang, L. J.; Yang, Y.; Fan, C. G.; Yin, W. Y.; Chen, J.; Zhang, Q. F. A green and facile route to synthesize calcium silicate nanowires. Mater. Charact. 2010, 61, 1281−1285. (63) Rodríguez-Lorenzo, L. M.; García-Carrodeguas, R.; Rodríguez, M. A.; De Aza, S.; Jiménez, J.; López-Bravo, A.; Fernandez, M.; Román, J. S. Synthesis, characterization, bioactivity and biocompatibility of nanostructured materials based on the wollastonitepoly(ethylmethacrylate-co-vinylpyrrolidone) system. J. Biomed. Mater. Res. A 2009, 88A, 53−64. (64) Wu, J.; Zhu, Y.-J.; Cheng, G.-F.; Huang, Y.-H. Microwaveassisted preparation of Ca6Si6O17(OH)2 and β-CaSiO3 nanobelts. Mater. Res. Bull. 2010, 45, 509−512. (65) Ling, H.; Liu, Q.; Chang, C.; Mao, D. Preparation of calcium silicate nanobelts and the in vitro behavior in a simulated body fluid. Chem. Lett. 2007, 36, 1090−1091. (66) Tang, J.; Cui, X.; Liu, Y.; Yang, X. Morphology-Controlled Synthesis of Monodisperse ZnO Troughs at the Air−Water Interface under Mild Conditions. J. Phys. Chem. B 2005, 109, 22244−22249. (67) Huczko, A. Template-based synthesis of nanomaterials. Appl. Phys. A: Mater. Sci. Process. 2000, 70, 365−376. (68) Shingubara, S. Fabrication of nanomaterials using porous alumina templates. J. Nanopart. Res. 2003, 5, 17−30. (69) Schönenberger, C.; van der Zande, B. M. I.; Fokkink, L. G. J.; Henny, M.; Schmid, C.; Krüger, M.; Bachtold, A.; Huber, R.; Birk, H.; Staufer, U. Template synthesis of nanowires in porous polycarbonate

procedures and performance improvement for water treatment. Environ. Pollut. 2010, 158, 2335−2349. (29) Alexandridis, P. Gold Nanoparticle Synthesis, Morphology Control, and Stabilization Facilitated by Functional Polymers. Chem. Eng. Technol. 2011, 34, 15−28. (30) Grzelczak, M.; Perez-Juste, J.; Mulvaney, P.; Liz-Marzan, L. M. Shape control in gold nanoparticle synthesis. Chem. Soc. Rev. 2008, 37, 1783−1791. (31) Hormozi-Nezhad, M. R.; Karami, P.; Robatjazi, H. A simple shape-controlled synthesis of gold nanoparticles using nonionic surfactants. RSC Adv. 2013, 3, 7726−7732. (32) Sun, Y.; Xia, Y. Shape-Controlled Synthesis of Gold and Silver Nanoparticles. Science 2002, 298, 2176−2179. (33) Beaudoin, J. J.; Raki, L.; Marchand, J. The use of compacts for durability investigation of cement-based materials. J. Mater. Sci. 2003, 38, 4957−4964. (34) Jun, Y.-w.; Choi, J.-s.; Cheon, J. Shape Control of Semiconductor and Metal Oxide Nanocrystals through Nonhydrolytic Colloidal Routes. Angew. Chem., Int. Ed. 2006, 45, 3414−3439. (35) Kahn, M. L.; Glaria, A.; Pages, C.; Monge, M.; Macary, L. S.; Maisonnat, A.; Chaudret, B. Organometallic chemistry: an alternative approach towards metal oxide nanoparticles. J. Mater. Chem. 2009, 19, 4044−4060. (36) Nguyen, T.-D. From formation mechanisms to synthetic methods toward shape-controlled oxide nanoparticles. Nanoscale 2013, 5, 9455−9482. (37) Nguyen, T.-D.; Do, T.-O. General Two-Phase Routes to Synthesize Colloidal Metal Oxide Nanocrystals: Simple Synthesis and Ordered Self-Assembly Structures. J. Phys. Chem. C 2009, 113, 11204−11214. (38) Obradors, X.; Puig, T.; Gibert, M.; Queralto, A.; Zabaleta, J.; Mestres, N. Chemical solution route to self-assembled epitaxial oxide nanostructures. Chem. Soc. Rev. 2014, 43, 2200−2225. (39) Niu, J.; Shen, H.; Li, X.; Xu, W.; Wang, H.; Li, L. S. Controlled synthesis of high quality PbSe and PbTe nanocrystals with one-pot method and their self-assemblies. Colloids Surf., A 2012, 406, 38−43. (40) Yong, K.-T.; Sahoo, Y.; Choudhury, K. R.; Swihart, M. T.; Minter, J. R.; Prasad, P. N. Shape Control of PbSe Nanocrystals Using Noble Metal Seed Particles. Nano Lett. 2006, 6, 709−714. (41) Sun, J.; Zhang, J.; Zhang, M.; Antonietti, M.; Fu, X.; Wang, X. Bioinspired hollow semiconductor nanospheres as photosynthetic nanoparticles. Nat. Commun. 2012, No. 1139. (42) Shaviv, E.; Schubert, O.; Alves-Santos, M.; Goldoni, G.; Di Felice, R.; Vallee, F.; Del Fatti, N.; Banin, U.; Sönnichsen, C. Absorption properties of Metal−Semiconductor hybrid nanoparticles. ACS Nano 2011, 5, 4712−4719. (43) Kim, J. J.; Foley, E. M.; Taha, M. M. R. Nano-mechanical characterization of synthetic calcium−silicate−hydrate (C−S−H) with varying CaO/SiO2 mixture ratios. Cem. Concr. Compos. 2013, 36, 65−70. (44) Moghaddam, S. E.; Hejazi, V.; Hwang, S. H.; Sreenivasan, S.; Miller, J.; Shi, B. H.; Zhao, S.; Rusakova, I.; Alizadeh, A. R.; Whitmire, K. H.; Shahsavari, R. Morphogenesis of cement hydrate. J. Mater. Chem. A 2017, 5, 3798−3811. (45) Mishra, R. K.; Mohamed, A. K.; Geissbuhler, D.; Manzano, H.; Jamil, T.; Shahsavari, R.; Kalinichev, A. G.; Galmarini, S.; Tao, L.; Heinz, H.; Pellenq, R.; van Duin, A. C. T.; Parker, S. C.; Flatt, R. J.; Bowen, P. cemff: A force field database for cementitious materials including validations, applications and opportunities. Cem. Concr. Res. 2017, 102, 68−89. (46) Tao, L.; Shahsavari, R. Diffusive, Displacive Deformations and Local Phase Transformation Govern the Mechanics of Layered Crystals: The Case Study of Tobermorite. Sci. Rep. 2017, 7, No. 5907. (47) Zhang, N.; Carrez, P.; Shahsavari, R. Screw-DislocationInduced Strengthening-Toughening Mechanisms in Complex Layered Materials: The Case Study of Tobermorite. ACS Appl. Mater. Interfaces 2017, 9, 1496−1506. (48) Zhang, N.; Shahsavari, R. Balancing strength and toughness of calcium-silicate-hydrate via random nanovoids and particle inclusions: K


Article

Langmuir membranes: electrochemistry and morphology. J. Phys. Chem. B 1997, 101, 5497−5505. (70) Roh, D. K.; Patel, R.; Ahn, S. H.; Kim, D. J.; Kim, J. H. Preparation of TiO2 nanowires/nanotubes using polycarbonate membranes and their uses in dye-sensitized solar cells. Nanoscale 2011, 3, 4162−4169. (71) Han, W.; Fan, S.; Li, Q.; Hu, Y. Synthesis of gallium nitride nanorods through a carbon nanotube-confined reaction. Science 1997, 277, 1287−1289. (72) Han, W.; Fan, S.; Li, Q.; Gu, B.; Zhang, X.; Yu, D. Synthesis of silicon nitride nanorods using carbon nanotube as a template. Appl. Phys. Lett. 1997, 71, 2271−2273. (73) Jana, N. R.; Gearheart, L.; Murphy, C. J. Seed-mediated growth approach for shape-controlled synthesis of spheroidal and rod-like gold nanoparticles using a surfactant template. Adv. Mater. 2001, 13, 1389. (74) Liu, Y.; Goebl, J.; Yin, Y. Templated synthesis of nanostructured materials. Chem. Soc. Rev. 2013, 42, 2610−2653. (75) Hwang, S. H.; Miller, J. B.; Shahsavari, R. Biomimetic, Strong, Tough, and Self-Healing Composites Using Universal SealantLoaded, Porous Building Blocks. ACS Appl. Mater. Interfaces 2017, 9, 37055−37063. (76) Bahri, M. A.; Hoebeke, M.; Grammenos, A.; Delanaye, L.; Vandewalle, N.; Seret, A. Investigation of SDS, DTAB and CTAB micelle microviscosities by electron spin resonance. Colloids Surf., A 2006, 290, 206−212. (77) Bergström, M.; Pedersen, J. S. Structure of pure SDS and DTAB micelles in brine determined by small-angle neutron scattering (SANS). Phys. Chem. Chem. Phys. 1999, 1, 4437−4446. (78) Patel, V.; Dharaiya, N.; Ray, D.; Aswal, V. K.; Bahadur, P. pH controlled size/shape in CTAB micelles with solubilized polar additives: A viscometry, scattering and spectral evaluation. Colloids Surf., A 2014, 455, 67−75. (79) Nooney, R. I.; Thirunavukkarasu, D.; Chen, Y. M.; Josephs, R.; Ostafin, A. E. Synthesis of nanoscale mesoporous silica spheres with controlled particle size. Chem. Mater. 2002, 14, 4721−4728. (80) Lin, H. P.; Kao, C. P.; Mou, C. Y. Counterion and alcohol effect in the formation of mesoporous silica. Microporous Mesoporous Mater. 2001, 48, 135−141. (81) Li, X.; Zhang, L. X.; Dong, X. P.; Liang, J.; Shi, J. L. Preparation of mesoporous calcium doped silica spheres with narrow size dispersion and their drug loading and degradation behavior. Microporous Mesoporous Mater. 2007, 102, 151−158. (82) Hunnicutt, W. A. Characterization of Calcium-Silicate-Hydrate and Calcium-Alumino-Silicate-Hydrate; University of Illinois at Urbana: Urbana, Illinois, 2013. (83) Alizadeh, R.; Beaudoin, J. J.; Raki, L. Mechanical properties of calcium silicate hydrates. Mater. Struct. 2011, 44, 13−28. (84) Villain, G.; Thiery, M.; Platret, G. Measurement methods of carbonation profiles in concrete: Thermogravimetry, chemical analysis and gammadensimetry. Cem. Concr. Res. 2007, 37, 1182−1192. (85) Mojumdar, S. C.; Raki, L. Synthesis, thermal and structural characterization of nanocomposites for potential applications in construction. J. Therm. Anal. Calorim. 2006, 86, 651−657. (86) Chi, J. M.; Huang, R.; Yang, C. C. Effects of carbonation on mechanical properties and durability of concrete using accelerated testing method. J. Mar. Sci. Technol. 2002, 10, 14−20. (87) Fabbri, A.; Corvisier, J.; Schubnel, A.; Brunet, F.; Goffe, B.; Rimmele, G.; Barlet-Gouedard, V. Effect of carbonation on the hydromechanical properties of Portland cements. Cem. Concr. Res. 2009, 39, 1156−1163. (88) Mehta, S. K.; Chaudhary, S.; Kumar, S.; Bhasin, K. K.; Torigoe, K.; Sakai, H.; Abe, M. Surfactant assisted synthesis and spectroscopic characterization of selenium nanoparticles in ambient conditions. Nanotechnology 2008, 19, No. 295601. (89) Tanford, C. The Hydrophobic Effect: Formation of Micelles and Biological Membranes, 2nd ed.; John Wiley & Sons, 1980.

(90) Moulik, S. P.; Haque, M. E.; Jana, P. K.; Das, A. R. Micellar properties of cationic surfactants in pure and mixed states. J. Phys. Chem. 1996, 100, 701−708. (91) Stö ber, W.; Fink, A.; Bohn, E. Controlled Growth of Monodisperse Silica Spheres in Micron Size Range. J. Colloid Interface Sci. 1968, 26, 62−69. (92) Wang, X. D.; Shen, Z. X.; Sang, T.; Cheng, X. B.; Li, M. F.; Chen, L. Y.; Wang, Z. S. Preparation of spherical silica particles by Stober process with high concentration of tetra-ethyl-orthosilicate. J. Colloid Interface Sci. 2010, 341, 23−29. (93) Wang, H. C.; Wu, C. Y.; Chung, C. C.; Lai, M. H.; Chung, T. W. Analysis of parameters and interaction between parameters in preparation of uniform silicon dioxide nanoparticles using response surface methodology. Ind. Eng. Chem. Res. 2006, 45, 8043−8048. (94) Poon, B.; Rittel, D.; Ravichandran, G. An analysis of nanoindentation in elasto-plastic solids. Int. J. Solids Struct. 2008, 45, 6399−6415. (95) Basheer, M.; Barbhuiya, S. Pore Structure and Transport Processes. Concrete Durability: A Practical Guide to the Design of Durable Concrete Structures; Thomas Telford, 2010. (96) Pileni, M.-P. Nanocrystal self-assemblies: fabrication and collective properties. J. Phys. Chem. B 2001, 105, 3358−3371. (97) Nikoobakht, B.; Wang, Z.; El-Sayed, M. Self-assembly of gold nanorods. J. Phys. Chem. B 2000, 104, 8635−8640. (98) Collier, C. P.; Vossmeyer, T.; Heath, J. P. Nanocrystal superlattices. Annu. Rev. Phys. Chem. 1998, 49, 371−404. (99) Murray, C.; Kagan, C.; Bawendi, M. Self-organization of CdSe nanocrystallites into three-dimensional quantum dot superlattices. Science 1995, 270, 1335−1338. (100) Singh, G.; Chan, H.; Baskin, A.; Gelman, E.; Repnin, N.; Král, P.; Klajn, R. Self-assembly of magnetite nanocubes into helical superstructures. Science 2014, 345, 1149−1153. (101) Li, M.; Wong, K. K.; Mann, S. Organization of inorganic nanoparticles using biotin-streptavidin connectors. Chem. Mater. 1999, 11, 23−26. (102) Liang, C.; Hong, K.; Guiochon, G. A.; Mays, J. W.; Dai, S. Synthesis of a Large-Scale Highly Ordered Porous Carbon Film by Self-Assembly of Block Copolymers. Angew. Chem., Int. Ed. 2004, 43, 5785−5789. (103) Cheng, J. Y.; Ross, C. A.; Smith, H. I.; Thomas, E. L. Templated Self-Assembly of Block Copolymers: Top-Down Helps Bottom-Up. Adv. Mater. 2006, 18, 2505−2521. (104) Pradhan, A.; Samantaray, C.; Mundle, R.; Birdsong, T.; Santiago, K.; Biswal, D.; Goornavar, V.; Ramesh, G. Self-Assembly of DNA Nanostructures on Electron Beam Lithographically Patterned Templates for Biomedical and Nanoelectronic Sensor Applications. J. Electrochem. Soc. 2014, 161, B3023−B3027. (105) Li, M.; Schnablegger, H.; Mann, S. Coupled synthesis and selfassembly of nanoparticles to give structures with controlled organization. Nature 1999, 402, 393−395. (106) Hwang, S. H.; Shahsavari, R. Intrinsic Size Effect in Scaffolded Porous Calcium Silicate Particles and Mechanical Behavior of Their Self-Assembled Ensembles. ACS Appl. Mater. Interfaces 2018, 10, 890−899. (107) Guo, W.; Wang, M.; Xia, W.; Dai, L. Evaporation-induced selfassembly of capillary cylindrical colloidal crystal in a face-centered cubic structure with controllable thickness. J. Mater. Res. 2012, 27, 1663−1671. (108) Ye, Y. H.; LeBlanc, F.; Hache, A.; Truong, V. V. Selfassembling three-dimensional colloidal photonic crystal structure with high crystalline quality. Appl. Phys. Lett. 2001, 78, 52−54. (109) Meijer, J. M.; Hagemans, F.; Rossi, L.; Byelov, D. V.; Castillo, S. I. R.; Snigirev, A.; Snigireva, I.; Philipse, A. P.; Petukhov, A. V. SelfAssembly of Colloidal Cubes via Vertical Deposition. Langmuir 2012, 28, 7631−7638. (110) Joannopoulos, J. D. Photonics: Self-assembly lights up. Nature 2001, 414, 257−258. L


Article

Langmuir (111) Shahsavari, R. Intercalated Hexagonal Boron Nitride/Silicates as Bilayer Multifunctional Ceramics. ACS Appl. Mater. Interfaces 2018, 10, 2203−2209. (112) Mehta, K. P. Reducing the Environmental Impact of Concrete. Concr. Int. 2001, 23, 61−66. (113) Shahsavari, R.; Hwang, S. H. Innovative concretes provide the ultimate solution for rising construction costs and environmental footprint. Am. Ceram. Soc. Bull. 2018, 97, 24−30. (114) Biernacki, J. J.; Bullard, J. W.; Sant, G.; Brown, K.; Glasser, F. P.; Jones, S.; Ley, T.; Livingston, R.; Nicoleau, L.; Olek, J.; Sanchez, F.; Shahsavari, R.; Stutzman, P. E.; Sobolev, K.; Prater, T. Cements in the 21(st) century: Challenges, perspectives, and opportunities. J. Am. Ceram. Soc. 2017, 100, 2746−2773. (115) Hwang, S. H.; Shahsavari, R. High calcium cementless fly ash binder with low environmental footprint: Optimum Taguchi design. J. Am. Ceram. Soc. 2018. DOI: 10.1111/jace.15873. (116) Shahsavari, R.; Chen, L.; Tao, L. Edge dislocations in dicalcium silicates: Experimental observations and atomistic analysis. Cem. Concr. Res. 2016, 90, 80−88. (117) Shahsavari, R.; Tao, L.; Chen, L. Structure, Energetics, and Impact of Screw Dislocations in Tricalcium Silicates. J. Am. Ceram. Soc. 2016, 99, 2512−2520. (118) Shahsavari, R.; Chen, L. Screw Dislocations in Complex, Low Symmetry Oxides: Core Structures, Energetics, and Impact on Crystal Growth. ACS Appl. Mater. Interfaces 2015, 7, 2223−2234. (119) Jalilvand, S.; Shahsavari, R. Molecular Mechanistic Origin of Nanoscale Contact, Friction, and Scratch in Complex Particulate Systems. ACS Appl. Mater. Interfaces 2015, 7, 3362−3372. (120) Rafiee, M. A.; Narayanan, T. N.; Hashim, D. P.; Sakhavand, N.; Shahsavari, R.; Vajtai, R.; Ajayan, P. M. Hexagonal Boron Nitride and Graphite Oxide Reinforced Multifunctional Porous Cement Composites. Adv. Funct. Mater. 2013, 23, 5624−5630. (121) Constantinides, G.; Ulm, F.-J. The nanogranular nature of C− S−H. J. Mech. Phys. Solids 2007, 55, 64−90. (122) Cariou, S.; Ulm, F.-J.; Dormieux, L. Hardness−packing density scaling relations for cohesive-frictional porous materials. J. Mech. Phys. Solids 2008, 56, 924−952. (123) Shahsavari, R.; Ulm, F.-J. Indentation analysis of fractional viscoelastic solids. J. Mech. Mater. Struct. 2009, 4, 523−550. (124) Kim, N. D.; Metzger, A.; Hejazi, V.; Li, Y.; Kovalchuk, A.; Lee, S.-K.; Ye, R.; Mann, J. A.; Kittrell, C.; Shahsavari, R.; Tour, J. M. Microwave Heating of Functionalized Graphene Nanoribbons in Thermoset Polymers for Wellbore Reinforcement. ACS Appl. Mater. Interfaces 2016, 8, 12985−12991. (125) Feldman, R. F. Factors affecting Young’s modulus - Porosity relation of hydrated Portland cement compacts. Cem. Concr. Res. 1972, 2, 375−386. (126) Beaudoin, J. J. Comparison of Mechanical-Properties of Compacted Calcium Hydroxide and Portland-Cement Paste Systems. Cem. Concr. Res. 1983, 13, 319−324. (127) Tedesco, J.; Ross, C. Strain-rate-dependent constitutive equations for concrete. J. Pressure Vessel Technol. 1998, 120, 398−405. (128) Lu, Y.; Li, Q. About the dynamic uniaxial tensile strength of concrete-like materials. Int. J. Impact Eng. 2011, 38, 171−180. (129) C09 Committee. ASTM C1202 Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration; ASTM International, 2012. (130) Zhang, J.; Wang, J.; Kong, D. Chloride diffusivity analysis of existing concrete based on Fick’s second law. J. Wuhan Univ. Technol., Mater. Sci. Ed. 2010, 25, 142−146. (131) Li, L.; Aubertin, M. A general relationship between porosity and uniaxial strength of engineering materials. Can. J. Civ. Eng. 2003, 30, 644−658.

M


Size- and Shape-Controlled Synthesis of Calcium Silicate Particles

Recommend Documents