Perfluorinated Alcohols at High Pressure: Experimental Liquid Density and Computer Simulations

The liquid density of five liquid 1H,1H-perfluorinated alcohols (CF3(CF2)n−1CH2OH n = 2, 3, 4, 5, 6) was measured as a function of pressure (0.1−70 MPa) and temperature (293.15−313.15 K). The corresponding isothermal compressibility and isobaric thermal expansivity coefficients were calculated from the experimental data. The results are compared with data from the literature for the equivalent hydrogenated alcohols. Atomistic molecular dynamics simulations were also performed, providing molecular-level insight into the experimental results, in particular about the H-bond network of the perfluorinated alcohols and the effect of pressure on the organization of the liquid

Molecular dynamics simulation studies of the interactions between ionic liquids and amino acids in aqueous solution

Although the understanding of the influence of ionic liquids (ILs) on the solubility behavior of biomolecules in aqueous solutions is relevant for the design and optimization of novel biotechnological processes, the underlying molecular-level mechanisms are not yet consensual or clearly elucidated. In order to contribute to the understanding of the molecular interactions established between amino acids and ILs in aqueous media, classical molecular dynamics (MD) simulations were performed for aqueous solutions of five amino acids with different structural characteristics (glycine, alanine, valine, isoleucine, and glutamic acid) in the presence of 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide. The results from MD simulations enable to relate the properties of the amino acids, namely their hydrophobicity, to the type and strength of their interactions with ILs in aqueous solutions and provide an explanation for the direction and magnitude of the solubility phenomena observed in [IL + amino acid + water] systems by a mechanism governed by a balance between competitive interactions of the IL cation, IL anion, and water with the amino acids

Tensile and compressive behavior of CHC-Reinforced copper using molecular dynamics

Graphene has been extensively studied as nanofiller to produce ultra-strong and ductile metal nanocomposites but challenges such as poor adhesion at the metal–carbon interface have yet to be met. Carbon honeycombs (CHCs) are highly porous3D graphene networks that possess a very large surface area-to-volume ratio, an outstanding physical absorption capacity and notable mechanical properties.Herein, these recently synthetized 3D CHCs are introduced in copper as nano-fillers, and the mechanical properties of the nanocomposites, such as elastic modulus, tensile strength, failure strain, compressive strength, and critical strain,are obtained using molecular dynamics simulations. Three CHC lattice types are studied, and the metal–carbon interface is accurately modeled by using melting and recrystallization of the copper matrix around the nanofiller. Gains between28% and 50% are obtained for the Young’s modulus, while the tensile strength improved between 43% and 49%. Pullout tests reveal that the copper nanopillars that form by the filling of the honeycomb cells of CHC by copper atoms considerably increase the pullout force and are responsible for improvements in adhesion and in loading stress transfer.This work was supported by FCT, through IDMEC, under LAETA (project no. UIDB/50022/2020); through Centro de Quimica Estrutural (CQE) (project nos. UIDB/00100/2020 and PTDC/QUI-QFI/28367/2017), under Institute of Molecular Sciences (project no. LA/P/0056/2020) and through IPC-Institute for Polymers and Composites. The first author gratefully acknowledges the financial support given by FCT in the context of (grant no. CEECINST/00156/2018)

A Transferable, Polarisable Force Field for Ionic Liquids

A general, transferable polarisable force field for molecular simulation of ionic liquids and their mixtures with molecular compounds is developed. This polarisable model is derived from the widely used CL\&P fixed-charge force field that describes most families of ionic liquids, in a form compatible with OPLS-AA, one of the major force fields for organic compounds. Models for ionic liquids with fixed, integer ionic charges lead to pathologically slow dynamics, a problem that is corrected when polarisation effects are included explicitly. In the model proposed here, Drude induced dipoles are used with parameters determined from atomic polarisabilities. The CL\&P force field is modified upon inclusion of the Drude dipoles, to avoid double-counting of polarisation effects. This modification is based on first-principles calculations of the dispersion and induction contributions to the van der Waals interactions, using symmetry-adapted perturbation theory (SAPT) for a set of dimers composed of positive, negative and neutral fragments representative of a wide variety of ionic liquids. The fragment approach provides transferability, allowing the representation of a multitude of cation and anion families, including different functional groups, without need to re-parametrise. Because SAPT calculations are expensive an alternative predictive scheme was devised, requiring only molecular properties with a clear physical meaning, namely dipole moments and atomic polarisabilities. The new polarisable force field, CL\&Pol, describes a broad set set of ionic liquids and their mixtures with molecular compounds, and is validated by comparisons with experimental data on density, ion diffusion coefficients and viscosity. The approaches proposed here can also be applied to the conversion of other fixed-charged force fields into polarisable versions.<br /

Molecular Modelling of Ionic Liquids.

International audienc

Ionic Liquids and Water: Hydrophobicity vs. Hydrophilicity

Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl [C3C1im][NTf2], butyl [C4C1im][NTf2] and isobutyl [iC4C1im][NTf2]) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of [C2C1im][CnF2n+1SO3], [C2C1im][CnH2n+1SO3], [C2C1im][CF3CO2] and [C2C1im][CH3CO2] (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium [N1 2OH 2OH 2OH]+, with high hydrogen-bonding capability, and the hydrophobic anion [NTf2]–. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs