Nanostructures of diverse chemical nature are used as biomarkers, therapeutics, catalysts, and structural reinforcements. The decoration with surfactants has a long history and is essential to ...introduce specific functions. The definition of surfactants in this review is very broad, following its lexical meaning “surface active agents”, and therefore includes traditional alkyl modifiers, biological ligands, polymers, and other surface active molecules. The review systematically covers covalent and non-covalent interactions of such surfactants with various types of nanomaterials, including metals, oxides, layered materials, and polymers as well as their applications. The major themes are (i) molecular recognition and noncovalent assembly mechanisms of surfactants on the nanoparticle and nanocrystal surfaces, (ii) covalent grafting techniques and multi-step surface modification, (iii) dispersion properties and surface reactions, (iv) the use of surfactants to influence crystal growth, as well as (v) the incorporation of biorecognition and other material-targeting functionality. For the diverse materials classes, similarities and differences in surfactant assembly, function, as well as materials performance in specific applications are described in a comparative way. Major factors that lead to differentiation are the surface energy, surface chemistry and pH sensitivity, as well as the degree of surface regularity and defects in the nanoparticle cores and in the surfactant shell. The review covers a broad range of surface modifications and applications in biological recognition and therapeutics, sensors, nanomaterials for catalysis, energy conversion and storage, the dispersion properties of nanoparticles in structural composites and cement, as well as purification systems and classical detergents. Design principles for surfactants to optimize the performance of specific nanostructures are discussed. The review concludes with challenges and opportunities.
Improvements in the sustainability and durability of building materials depend on understanding interfacial properties of various mineral phases at the nanometer scale. Tricalcium silicate (C3S) is ...the major constituent of cement clinker and we present and validate a force field for atomistic simulations that provides excellent agreement with available experimental data, including X-ray structures, cleavage energies, elastic moduli, and IR spectra. Using this model and available measurements, we quantify key surface and interface properties of the dry and superficially hydrated mineral. An extensive set of possible cleavage planes shows cleavage energies in a range of 1300 to 1600 mJ/m2 that are consistent with the observation of faceted crystallites with an aspect ratio near one. Using pure and hydroxylated surface models that represent the first step in the hydration reaction, we examined the adsorption mechanism of several organic amines and alcohols at different temperatures. Strong attraction between −20 and −50 kcal/mol is found as a result of complexation of superficial calcium ions, electrostatic interactions, and hydrogen bonds on the ionic surface. Agglomeration of cleaved C3S surfaces in the absence of organic molecules was found to recover less than half the original cleavage energy (∼450 mJ/m2) associated with reduced Coulomb interactions between reconstructed surfaces. Additional adsorption of organic compounds below monolayer coverage reduced the attraction between even surfaces to less than 5% of the original cleavage energy (∼50 mJ/m2) related to their action as spacers between cleaved surfaces and mitigation of local electric fields. Computed agglomeration energies for a series of adsorbed organic compounds correlate with the reduction in surface forces in the form of measured grinding efficiencies. The force field is extensible to other cement phases and compatible with many platforms for molecular simulations (PCFF, COMPASS, CHARMM, AMBER, OPLS-AA, CVFF).
We used a combination of experimental and modelling techniques to study the effect of NaAlO2 on C3S hydration. pH sensitive inhibition of C3S hydration occurred at an early age of reaction, but was ...followed by an increased amount of hydrates formed later. Most results suggest that aluminates hinder C3S dissolution. It is hypothesised that this takes place in active dissolution areas, present with a higher density on finer particles. Annealing reduces their number and increases retardation for a given dosage of aluminates. The view that aluminates act by hindering dissolution is supported by molecular dynamics (MD) simulations. They establish that aluminates can adsorb on the hydroxylated C3S mainly through strong ionic interactions between aluminate and calcium ions on the surface of silicate. Upon progress of hydration and at higher pH values, the binding strength of aluminates to the hydroxylated C3S decreases so that its passivating effect, and retardation, are reduced.
This paper reviews atomistic force field parameterizations for molecular simulations of cementitious minerals, such as tricalcium silicate (C3S), portlandite (CH), tobermorites (model C-S-H). ...Computational techniques applied to these materials include classical molecular simulations, density functional theory and energy minimization. Such simulations hold promise to capture the nanoscale mechanisms operating in cementitious materials and guide in performance optimization. Many force fields have been developed, such as Born–Mayer–Huggins, InterfaceFF (IFF), ClayFF, CSH-FF, CementFF, GULP, ReaxFF, and UFF. The benefits and limitations of these approaches are discussed and a database is introduced, accessible via a web-link (http://cemff.epfl.ch). The database provides information on the different force fields, energy expressions, and model validations using systematic comparisons of computed data with benchmarks from experiment and from ab-initio calculations. The cemff database aims at helping researchers to evaluate and choose suitable potentials for specific systems. New force fields can be added to the database.
•Development of cemff database to improve the accuracy of atomistic simulations and guide in performance optimization of cementitious systems.•Concepts and atomistic force field parameterizations of cementitious minerals.•Atomistic model validations and comparison between the computed data and benchmarks (experimental or ab-initio).•Different force fields (ClayFF, IFF, CementFF, ReaxFF and C-S-H FF) are compared. The benefits and limitations of these approaches are discussed.•Relationships between structure, properties, and applications are discussed.
Calcium sulfates such as anhydrite, hemihydrate, and gypsum find widespread use in building materials, implants, and tissue healing. We introduce a simple and compatible atomistic force field for all ...calcium sulfate phases that reproduces a wide range of experimental data including lattice parameters, surface, hydration, mechanical, and thermal properties in 1% to 5% accuracy relative to experiments. The performance is several times better than prior force fields and DFT methods, which lead to errors in structures and energies up to 100%. We explain (hkl) cleavage energies, the dynamics of (hkl) water interfaces, and new insights into molecular origins of crystal-facet specific hydration and solubility. Impressive agreement of computed and experimentally measured hydration energies is shown. The models add to the Interface force field (IFF) and are compatible with multiple force fields (CHARMM, AMBER, GROMOS, CVFF, PCFF, OPLS-AA) for property predictions of sulfate-containing materials from atoms to the large nanometer scale.
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Chemical admixtures are an essential ingredient of modern concrete mix, but many of their molecular scale working mechanisms remain poorly described. In this respect, recent advances in computational ...methods, provide a unique opportunity to gain the needed molecular level insights into the mechanism of action of chemical admixtures in cementitious systems. Such studies are slowly increasing in number and this paper proposes a review on approaches that deal with molecular simulations of chemical admixtures. The key properties studied so far are mainly adsorption behaviors and conformations of monomers, oligomers and polymers (molecular weight ~ 10,000 g/mol). Our aim is to identify opportunities, challenges and give perspectives on the future of molecular modeling of chemical admixture-cement interactions.
This paper is a discussion of a recent publication by Sekkal and coworkers, which investigated the elasticity, cohesion, and stability of the C-S-H (001) surface as a function of porosity using ...molecular dynamics simulations. In our discussion, we highlight some doubts about their model system for the C-S-H structure. We also comment on the defined stoichiometry, applied methodology and on various incongruous results and erroneous interpretations. We also draw attention to the lack of fundamental details provided by the authors and how it could be improved both conceptually and practically to allow readers to better understand the paper.
The simulation of metals, oxides, and hydroxides can accelerate the design of therapeutics, alloys, catalysts, cement-based materials, ceramics, bioinspired composites, and glasses. Here we introduce ...the INTERFACE force field (IFF) and surface models for α-Al2O3, α-Cr2O3, α-Fe2O3, NiO, CaO, MgO, β-Ca(OH)2, β-Mg(OH)2, and β-Ni(OH)2. The force field parameters are nonbonded, including atomic charges for Coulomb interactions, Lennard-Jones (LJ) potentials for van der Waals interactions with 12–6 and 9–6 options, and harmonic bond stretching for hydroxide ions. The models outperform DFT calculations and earlier atomistic models (Pedone, ReaxFF, UFF, CLAYFF) up to 2 orders of magnitude in reliability, compatibility, and interpretability due to a quantitative representation of chemical bonding consistent with other compounds across the periodic table and curated experimental data for validation. The IFF models exhibit average deviations of 0.2% in lattice parameters, <10% in surface energies (to the extent known), and 6% in bulk moduli relative to experiments. The parameters and models can be used with existing parameters for solvents, inorganic compounds, organic compounds, biomolecules, and polymers in IFF, CHARMM, CVFF, AMBER, OPLS-AA, PCFF, and COMPASS, to simulate bulk oxides, hydroxides, electrolyte interfaces, and multiphase, biological, and organic hybrid materials at length scales from atoms to micrometers. The nonbonded character of the models also enables the analysis of mixed oxides, glasses, and certain chemical reactions, and well-performing nonbonded models for silica phases, SiO2, are introduced. Automated model building is available in the CHARMM-GUI Nanomaterial Modeler. We illustrate applications of the models to predict the structure of mixed oxides, and energy barriers of ion migration, as well as binding energies of water and organic molecules in outstanding agreement with experimental data and calculations at the CCSD(T) level. Examples of model building for hydrated, pH-sensitive oxide surfaces to simulate solid-electrolyte interfaces are discussed.
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