A zwitterionic-based chemical, the 3,3’-(octadecylamino)dipropionic acid, was quantum-theoretically designed to be applied as a corrosion inhibitor for protecting oxidized iron surfaces against the ...attack of very corrosive gasolines. Its performance, as well as those of worldwide-employed nitrogen-free carboxylic-diacid-based corrosion inhibitors, were experimentally evaluated and compared. Through Density-Functional-Theory calculations of the molecular interactions of the corrosion inhibitors with an iron-oxide cluster model, along with the experimental corrosion-inhibiting evaluations, it is revealed that the zwitterionic-based chemical substantially overcomes the performance of nitrogen-free chemicals. It is shown by the theoretical results that the two carboxylic heads of either, the zwitterionic-based or the nitrogen-free corrosion inhibitors, reinforce the octahedral coordination around the exposed Fe3+ atom of the iron oxide. Furthermore, when the zwitterionic-based chemical is bonded to the Fe3+ atom, a two-rings chelate is formed, in contrast to the one-ring chelate formed by the nitrogen-free corrosion inhibitors. Finally, it is theoretically predicted that oleic solvents improve the performance of the zwitterionic-based corrosion inhibitor because preclude the steric hindrance of nitrogen.
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•Corrosion inhibitors based on dicarboxylic acids form one-ring chelates with Fe3+.•Zwitterionic inhibitors based on dipropionic acids form two-ring chelates with Fe3+.•Corrosion-inhibitor performing of zwitterions overcome that of dicarboxylic compounds.
The electronic structure and proton affinities of a series of organosulfur compounds such as thiophene, dibenzothiophene and a series of their derivatives have been studied by means density ...functional theory. The molecular structure of these compounds and their protonated species has been obtained by means of geometry optimization and characterized as potential energy surface minima by harmonic frequency analysis. The analysis of frontier orbitals, aromaticity and proton affinity permits one to make quantitative predictions about the difficulty to remove sulfur from these molecules. In particular, it is suggested that the proton affinities provide a descriptor of the activity of these molecules towards hydrodesulfurization.
Highest occupied molecular orbital (HOMO), (a) thiophene, (b) benzothiophene, (c) dibenzothiophene and (d) 4,6-dimethyldibenzothiophene at B3LYP/6-311++G** level of theory.
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Molecular modeling and computer simulations were used to construct, visualize, control and predict nanostructures with specific morphologies, self-assembling regions and mechanical properties ...associated to poly(styrene)–poly(isoprene) and poly(styrene)–poly(methyl methacrylate) diblock copolymers. Molecular structures of each diblock copolymer were constructed and used to obtain a Gaussian chain constituted of beads. Segment–segment interactions representing the chemical nature of the systems were obtained by means of numerical simulations. The numerical simulations for the two diblock systems predict structures with classic morphologies like bcc, hex, lamellar or gyroids and also other partial structure like islands and labyrinths. Young, bulk and shear modulus were also predicted from the structure and composition of the copolymer generating these morphologies. The excellent agreement between numerical and available experimental results opens a new strategy to modify existing diblock copolymer synthetic chemical processes to obtain products with specific morphologies.
Formation of metastable microphases during the order–order transition (OOT) pathway of gyroid-to-lamellar state of poly(styrene)–poly(isoprene) copolymer in bulk state.
The formation of metastable ...microphases during the order–order transition (OOT) from gyroid-to-lamellar states of a poly(styrene)–poly(isoprene) (PS–PI) copolymer has been investigated on a mesoscopic level using dissipative particle dynamics simulations. The formation of the gyroid microphase was obtained via an order–disorder transition process (ODT). The microphase was then subjected to thermal heating cycles. A thermodynamic instability of poly(styrene) microdomains due to temperature effects induces anisotropic composition fluctuations in the gyroid structure and a microphase transformation from gyroid-to-lamellar takes place via an OOT. Two metastable microphases (hexagonal perforated layers and cylinders) were detected during the thermal process. Results are consistent with experimental and theoretical studies.
The objective of this work is to provide some elements for developing a theoretical methodology aimed to describe the ion conductivity mechanism of chitosan membrane and to obtain its magnitude. ...Atomistic molecular modeling has been utilized to construct an ionic-conducting polymer–electrolyte system consisting of chitosan, H
2O molecules and H
3O
+, OH
−,
SO
4
2
−
ions, inside of the simulation cell. The COMPASS force field was used. The simulation allows describing the ionic conductivity mechanism along the polymer matrix. The theoretical results obtained are compared with previously reported experimental data for chitosan membranes. The present methodology can be considered as a first step towards understanding these complex problems of technological interest.
We present the quantum mechanics-based understanding about the formation of gums deposits in order to design, and then carry out the experimental synthesis of a detergent-dispersant (DD) gasoline ...additive base n-alkenyl imino di-propionic acid, obtained in mixture with its precursor base n-alkenyl amino propionic acid, aimed both to inhibit gums deposits within internal-combustion engines and maintain in suspension gums inside gasoline. Density Functional Theory reveals the cohesion among gums agglomerates is mediated mainly through dispersion forces, that is, gums form supramolecular complexes; likewise, their affinity for oxidized metallic surfaces is predominantly due also to the dispersion forces, but intensified through the linking of the gums' oxygens by the exposed metallic-surface irons, which is quantum driven to maximize irons spin through completing the truncated oxygen octahedral coordination, so providing to the gums' adsorption a mixed chemisorption/physisorption character. Additionally, carbons from double bonds C=C or from aromatic rings, as well as aminic hydrogens, contribute by means of weak semicovalent bonds to the gums’ chemisorption too. We take advantage of this acquired knowledge to outline a superior coordination chemistry to that of gums for the above deposits inhibitor, lying on the capability to form either trinuclear-tridentate or binuclear-bidentate surface complexes, reinforced moreover by a six-membered chelate ring containing an iron cation. The additive was lab synthesized by means of an industrial-scale residues-less process, and characterized through 1H and 13C nuclear magnetic resonance along with infrared spectroscopy. The detergent performance, experimentally tested within the intake valve of a single-cylinder engine, shows that the DD additive inhibits up to 93.3% of the gums deposition.
The interaction between a series of p-alkyl phenols with the solvent n-heptane (n-C7) is studied by means of theoretical methods. The solvation energies of these molecules are computed using quantum ...mechanical methods in which the solvent is considered as a dielectric medium. Accordingly, the interaction of a solute molecule with the reaction field of the solvent yields a solvation free energy. The electrostatic, dispersion, and repulsion contributions to the solvation energies are analyzed as a function of the alkyl chain length and the relationship with the electronic structure of the molecules, as accounted for by the properties of the quantum topological atoms defined within the formalism of the atoms in molecules theory, is also discussed. Implications of the solvation energies, computed at the microscopic level, on the efficiency of p-alkyl phenols as asphaltene dispersants are discussed. The quantitative aspects of the solubility of these amphiphiles are correlated with their experimentally reported dispersing power of an asphaltene of a given oil source in n-C7. These observations support the hypothesis that the relative ability of a series of p-alkyl phenols to dissolve a given asphaltene in n-C7 is dominated by the amphiphile−solvent interactions, which are sufficient to offset the repulsion and cavitation contributions.
•Enhanced oil recovery (EOR) by the employment of tetraalkyl ammonium chloride (C12TAC).•Theoretical and experimental viewpoints as mechanism for the enhancement of oil recovery.•Oil/oil–water ...wetting of calcite surface induced by heavy oils with high asphaltene content.•Oil disaggregation and viscosity reduction induced by ion–dipole pair formation.
Herein were performed theoretical and experimental studies about the performance of the cationic surfactant docecyltrimethylammonium chloride (C12TAC) on the enhancement of the oil recovery factor (ORF) from heavy oil-impregnated calcite cores. The interaction energies between C12TAC and either of some molecules present in oil such as an asphaltene (Asph), a resin (Res) or an octanoic acid, and among these and a calcite surface were theoretically determined within the framework of the Density Functional Theory. Experimental analysis based on Fourier transform infrared (FTIR) spectroscopy as well as 1H and 13C nuclear magnetic resonance (NMR) spectra were made on the heavy crude oil recovered by spontaneous imbibition tests from the calcite cores. Results evidenced that, by using brine containing 2.9ppm×105ppm of total ion, it were obtained ORF values of 8.9% at 90°C temperature and atmospheric pressure, and 36% at 150°C temperature and 145psi pressure. Meanwhile with the inclusion of C12TAC at the same temperature and pressure conditions used in pure brine experiments, noticeable increased ORF values of 36% and 44%, respectively, were found. From the molecular interaction strengths between C12TAC and the fractions present in the oil, it has been evidenced also the oil disaggregation as well as the subsequent oil viscosity reduction, but finally without significant wettability alteration of the calcite core. A saturated, aromatics, resins and asphaltenes (SARA) component analysis revealed a significant change in composition moving from their original values of 20.6, 21.0, 35.5 and 22.9%, respectively, to 31.0, 23.2, 28.7 and 17.2%, accordingly. The lack of wettability alteration of C12TAC in such process is due to a weak interaction in C12TAC:Res and C12TAC:Asph molecular pairs followed by a clear diminishment of Res and Asph fractions in SARA, which reveals Asph and Res cannot be removed from rock surface. The quantum nature of the supramolecular assembling between the cationic surfactant and oil molecules is described by molecular orbitals analysis.
A combined study for understanding the molecular interactions of asphaltenes with molecular species such as ionic liquids (ILs) comprised experimental measurements and computational numerical ...simulation calculations, using Density-Functional Theory (DFT) with dispersion corrections, molecular dynamics (MD) calculations and experimental rheological characterization of the heavy crude oils (HCOs), before and after doping with ILs, respectively. The main results show that ILs influence the asphaltenic dimmers association by forming supramolecular complexes that modify the properties of crude oils such as viscosity and interfacial tension. The (ILs)-cation and Asphaltene-π ligands molecular interactions seem dominating the interactions between ionic liquids and asphaltenes, where ILs' high aromaticity index induces a strong interaction with the aromatic hard core of asphaltenes.
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