Interaction of ethylene glycol–water clusters with aromatic surfaces

The gas phase geometries of ethylene glycol–water (EGmWn(where m = 0–4, n = 0–4; m + n ≤ 4) clusters adsorbed on a fragment of carbon nanotube have been investigated using density functional theory based M05-2X and ωB97XD methods employing various basis sets. With a view to assess the effect of curvature on the hydrogen bonding pattern between ethylene glycol and water molecules, calculations on intermolecular complexes comprising a planar aromatic surface and EGmWn clusters have been carried out. Results obtained from the electronic structure calculations and Bader's electron density analysis reveal that C–H⋯π, O–H⋯π and lone pair⋯π interactions are predominant in the stabilization of EGmWn and the corresponding complexes with fragments of a carbon nanotube and graphene. Further, the role of the π-cloud on the stability of EGmWn is illustrated by comparing the interaction energies of clusters in the presence and absence of an aromatic surface

Adsorption of guanidinium collectors on aluminosilicate minerals – a density functional study

In this density functional theory based investigation, we have modelled and studied the adsorption behaviour of guanidinium cations and substituted (phenyl, methoxy phenyl, nitro phenyl and di-nitro phenyl) guanidinium cationic collectors on the basal surfaces of kaolinite and goethite. The adsorption behaviour is assessed in three different media, such as gas, explicit water and pH medium, to understand the affinity of GC collectors to the SiO<SUB>4</SUB> tetrahedral and AlO<SUB>6</SUB> octahedral surfaces of kaolinite. The tetrahedral siloxane surface possesses a larger binding affinity to GC collectors than the octahedral sites due to the presence of surface exposed oxygen atoms that are active in the intermolecular interactions. Furthermore, the inductive electronic effects of substituted guanidinium cations also play a key role in the adsorption mechanism. Highly positive cations result in a stronger electrostatic interaction and preferential adsorption with the kaolinite surfaces than low positive cations. Computed interaction energies and electron densities at the bond critical points suggest that the adsorption of guanidinium cations on the surfaces of kaolinite and goethite is due to the formation of intra/inter hydrogen bonding networks. Also, the electrostatic interaction favours the high adsorption ability of GC collectors in the pH medium than gas phase and water medium. The structures and energies of GC collectors pave an intuitive view for future experimental studies on mineral flotation

Effects of functionalization of carbon nanotubes on their dispersion in an ethylene glycol–water binary mixture – a molecular dynamics and ONIOM investigation

The present work utilizes classical molecular dynamics simulations to investigate the covalent functionalization of carbon nanotubes (CNTs) and their interaction with ethylene glycol (EG) and water molecules. The MD simulation reveals the dispersion of functionalized carbon nanotubes and the prevention of aggregation in aqueous medium. Further, residue-wise radial distribution function (RRDF) and atomic radial distribution function (ARDF) calculations illustrate the extent of interaction of –OH and –COOH functionalized CNTs with water molecules and the non-functionalized CNT surface with EG. As the presence of the number of functionalized nanotubes increases, enhancement in the propensity for the interaction with water molecules can be observed. However, the same trend decreases for the interaction of EG molecules. In addition, the ONIOM (M06-2X/6-31+G**:AM1) calculations have also been carried out on model systems to quantitatively determine the interaction energy (IE). It is found from these calculations that the relative enhancement in the interaction of water molecules with functionalized CNTs is highly favorable when compared to the interaction of EG

Interaction of carbon nanotube with ethylene glycol–water binary mixture: a molecular dynamics and density functional theory investigation

Classical molecular dynamics (MD) simulation has been carried out on model systems composed of ethylene glycol (EG) and carbon nanotube (CNT) in water (WAT) medium to gain insight into the interaction between them. The analysis of the MD results reveals that the EG molecules aggregate around CNT expelling water molecules due to the hydrophobic–hydrophobic interaction. Hydrogen-bonding (H-bonding) interaction between two EG molecules increases in the presence of CNT. Further, the presence of CNT decreases the solubility of EG in water. The analysis of the dihedral angle of EG reveals that the CNT induces conformational changes in EG. Specifically, a small fraction of the gauche form of EG is converted into trans. In addition, electronic structure calculations have also been carried out on model systems to quantitatively determine the binding energy (BE). The M05-2X/6-31+G** level calculations on the model systems show that the BE of CNT–WAT and CNT–EG ranges from 11.76 to 17.78 kJ/mol. It is interesting to note from the electronic structure calculations that the BE of trans EG with CNT is more than that of gauche EG with CNT in accordance with the findings from the MD simulation

On the perturbation of the H-bonding interaction in ethylene glycol clusters upon hydration

Ab initio and density functional methods have been employed to study the structure, stability, and spectral properties of various ethylene glycol (EG<SUB>m</SUB>) and ethylene glycol–water (EG<SUB>m</SUB>W<SUB>n</SUB>) (m = 1–3, n = 1–4) clusters. The effective fragment potential (EFP) approach was used to explore various possible EG<SUB>m</SUB>W<SUB>n</SUB> clusters. Calculated interaction energies of EG<SUB>m</SUB>W<SUB>n</SUB> clusters confirm that the hydrogen-bonding interaction between EG molecules is perturbed by the presence of water molecules and vice versa. Further, energy decomposition analysis shows that both electrostatic and polarization interactions predominantly contribute to the stability of these clusters. It was found from the same analysis that ethylene glycol–water interaction is predominant over the ethylene glycol–ethylene glycol and water–water interactions. Overall, the results clearly illustrate that the presence of water disrupts the ethylene glycol–ethylene glycol hydrogen bonds

On the Perturbation of the H-Bonding Interaction in Ethylene Glycol Clusters upon Hydration

Ab initio and density functional methods have been employed to study the structure, stability, and spectral properties of various ethylene glycol (EG<i>_m</i>) and ethylene glycol–water (EG_<i>m</i>W_<i>n</i>) (<i>m</i> = 1–3, <i>n</i> = 1–4) clusters. The effective fragment potential (EFP) approach was used to explore various possible EG_<i>m</i>W_<i>n</i> clusters. Calculated interaction energies of EG_<i>m</i>W_<i>n</i> clusters confirm that the hydrogen-bonding interaction between EG molecules is perturbed by the presence of water molecules and vice versa. Further, energy decomposition analysis shows that both electrostatic and polarization interactions predominantly contribute to the stability of these clusters. It was found from the same analysis that ethylene glycol–water interaction is predominant over the ethylene glycol–ethylene glycol and water–water interactions. Overall, the results clearly illustrate that the presence of water disrupts the ethylene glycol–ethylene glycol hydrogen bonds