Browsing by Author "Iza, Peter"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    A Computational Chemistry Approach to the Molecular Design of SiO2 Nanoparticles Coated with Stearic Acid and Sodium Stearate in Ethanol Solvent.
    (2023) Galarza-Acosta, Gabriela L.; Parra, Jose G.; Hernandez-Bravo, Raiza; Iza, Peter; Schott, Eduardo; Zarate, Ximena; Castillo, Jimmy; Mujica, Vladimiro
    Preparation of hydrophobic SiO2 nanoparticles (NPs) coated with different surfactants is important due to their potential application in different fields of chemistry. In this work, a combined experimental and Molecular Dynamics (MD) simulation approach, is advanced to characterize the adsorption process, in ethanol as a solvent, of stearic acid and sodium stearate on SiO2 spherical NPs with different ionization degrees (0%, 10%, and 23.3%). The main objective is to gain molecular insight into the factors involved in the preparation of hydrophobic coated NPs, which involves the intervention of ion-dipole, electrostatic, and hydrogen bond-type interactions depending on the surfactants and the nature SiO2 NPs. Our results demonstrate that the SiO2 NPs have a good affinity for ethanol solvent medium., as confirmed through the analysis of the Radial Distribution Functions (RDFs)), which indicates that hydrogen bonds are formed at a distance of similar to 0.192 nm between ethanol and SiO2 NPs. The presence of Na+ ions reduce the electrostatic repulsion between the -COO- and -SiO- groups in NPs with degrees of ionization of 10% and 23.3%, because it acts as a bridge and thus favors the adsorption between the silanol and carboxylic groups. The investigation of the Potentials of Mean Force (PMFs) suggests that the adsorption on these NPs, is a spontaneous process compared with the case with 0% ionization degree. The experimental coating of the NPs was studied using Atomic Force Microscopy (AFM), a technique that allows the indirect measure of the Work of Adhesion (W-adh), a key quantity to estimate the energy needed to separate the interfaces AFM tip-sample. The experimental values of W-adh for the pure SiO2 NPs and two modified SiO2 NPs correspond to 2.01 J/m(2), 1.72 J/m(2) and 1.43 J/m(2), respectively. The main conclusion is that the interaction energies between surfactants and SiO2 NPs, estimated from MD simulations, and the W-adh obtained from AFM measurements are correlated, in the sense that the reduction in the W-adh, in a solvent-free environment, corresponds to an increment of the interaction energy in the presence of the solvent. This reduction in W-adh is also associated with the fact that the nature of the coating of the SiO2 NPs surfaces increases the NPs hydrophobicity. Our analysis provides a path for the computational design and the prediction of hydrophobicity of coated NPs, which is the main focus of our work.
  • No Thumbnail Available
    Item
    Evaluation of the affinity of asphaltene molecular models A1 and A2 by the water/oil interfaces based on a novel concept of solubility parameter profiles obtained from MD simulations
    (2023) Parra, Jose G.; Rodriguez, Geraldine; Iza, Peter; Zarate, Ximena; Schott, Eduardo
    Crude oils are formed of asphaltenes that are species soluble in certain solvents such as toluene. The dis-tribution of asphaltene models and their mixtures in water/n-heptane and water/toluene systems were explored with MD simulations. A1 and A2 asphaltene models were used for the exploration of the affinity of these compounds by the water/oil interfaces. For this, a novel concept called solubility parameter pro-files was used to characterize the polarity of the regions present in water/n-heptane and water/toluene systems. Molecules of asphaltene models, n-heptane, and toluene were described with the GROMOS53A6 force field and CHELPG atomic charges, and water molecules with the SPC model. The prediction of the affinity of A1 and A2 asphaltene models at interfaces was determined using the total solubility parameter differences calculated between these species and solvent molecules. Calculated solubility parameters show a good correlation with experimental values. Total solubility parameter differences equal to 6,dtotal = 3.76 MPa0'5 and 6,dtotal = 0.36 MPa0'5 at the water/n-heptane interface suggest that asphaltene models have a good affinity by the water/n-heptane interface in comparison with the water/toluene interface whose values were 6,dtotal = 5.82 MPa0'5 and 6,dtotal = 9.94 MPa0'5 for A1 and A2 asphaltene mod-els, respectively. It was demonstrated that the affinity of asphaltenes by a specific region of the immis-cible system is controlled by the electrostatic and dispersive contributions associated with the solubility parameter profiles.(c) 2023 Elsevier B.V. All rights reserved.
  • No Thumbnail Available
    Item
    Unveiling the hydrophilic nature of SDS surfactant through molecular simulations: Exploring the influence of charge distribution on interfacial properties in the vacuum/SDS/water system
    (2024) Parra, Jose G.; Iza, Peter; Dominguez, Hector; Schott, Eduardo; Zarate, Ximena
    The hydrophilicity of SDS surfactant was evaluated using different charge distributions derived from atomic charges obtained by quantum mechanical calculations. The atomic charges were determined using the Hirshfeld, CM5, CHELPG, and Merz-Kollman methods. The results indicate that the correct charge distribution in the hydrophilic group has an impact on the description of the surfactant hydrophilicity, which allows us to obtain a good estimation of the interfacial properties of the vacuum/SDS/water system. Two models of charge distribution based on the point charge model were proposed for SDS surfactant, using atomic charges computed through Quantum Mechanical calculations. The charge distributions derived from CM5, Merz-Kollman, and CHELPG atomic charges consistently predict the interfacial properties such as: area occupied per molecule, interfacial thicknesses, and radial distribution functions. Using Molecular Dynamics simulations, the ability of the charge distributions combined with nonbonded parameters of the GROMOS53A6 force field to predict the interfacial properties has the following order: CM5 > Merz-Kollman approximate to CHELPG > Hirshfeld. In contrast, the charge distributions overestimated the reduction of the interfacial tension of the vacuum/SDS/water system. Interfacial properties such as interfacial tension, area occupied per SDS molecule, and molecular interaction between the hydrophilic headgroup and water molecules were evaluated. Simulations demonstrated that the high interfacial activity of the SDS surfactant is associated with the high negative charge distribution defined for the hydrophilic headgroup of the surfactant, which enhances the ability to attract water molecules and the solvation of the hydrophilic region.