Mechanical characterization of polymer-grafted graphene PEG nanocomposites using molecular dynamics

Available online 28 February 2024It is known that most polymers exhibit poor interfacial compatibility with graphene sheets. Modification of graphene's surface by functionalization with small polymer chains from the same building blocks as the matrix polymer improves the compatibility of graphene in polymeric materials. In this paper, the mechanical behaviour of polyethylene glycol (PEG) nanocomposites with graphene grafted with polymeric chains under tensile and compression is investigated using molecular dynamics. The influence of the functional groups (-NH2 and –OH) that bond the polymer chain to graphene is analysed. It is found that the system containing the –NH2 functional group showed lower mechanical properties than the system containing the –OH functional group. The mechanical properties of five PEG-nanocomposites are investigated: PEG/G, PEG/GNH-1PEG-S, PEG/GNH-2PEG-L, PEG/GNH-1PEG-S-NH2, PEG/GO-1PEG-S. The radius distribution function values and the variation of interfacial interaction energy are also examined. It is shown that functionalization of the graphene sheet increases the magnitude of the interaction energy, and it also reveals higher adhesion between graphene surface and PEG matrix. It is found that the mechanical properties of PEG are mostly improved in the longitudinal direction (reinforcement up to 43 %). Despite the high interaction between the nanofiller and PEG matrix, the low intrinsic properties of the nanofiller, namely Young's modulus, as well as the rupture of the graphene sheet during the deformation process deteriorated the mechanical properties of the nanocomposite. The presence of polymeric chains grafted to graphene improves the adhesion between the graphene surface and the polymeric matrix but decreases its mechanical properties.This work was supported by FCT, through IDMEC, under LAETA, project UIDB/50022/2020 [Grant No. 10.54499/UIDB/50022/2020], through Centro de Química Estrutural (CQE), project UIDB/00100/2020 and through Institute for Polymers and Composites, and through IDMEC, under LAETA, project UIDP/50022/2020 [Grant No. 10.54499/UIDP/50022/2020]. The first author gratefully acknowledges the financial support given by FCT in the context of the PhD scholarship SFRH/BD/129589/2017. The second author gratefully acknowledges the financial support given by FCT in the context of the Postdoctoral contract CEECINST/00156/2018

An MD Simulation Study

The authors thank the financial support from Fundação para a Ciência e Tecnologia, FCT/MCTES (Portugal) through the projects UIDB/00100/2020, UIDP/00100/2020, LAETA, UIDB/50022/2020, UID/QUI/50006/2019 (Associate Laboratory for Green Chemistry-LAQV-REQUIMTE), PTDC/QUI-QFI/29527/2017, and IMS-LA/P/0056/2020, through CEEC contracts (IST-ID/100/2018 to K.S. and IST-ID/93/2018 to A.A.F.) and the PhD grant SFRH/BD/140079/2018 from M.T.D. Publisher Copyright: © 2024 The Authors. Published by American Chemical SocietyThe unique physicochemical properties of ionic liquids (ILs) attracted interest in their application as lubricants of micro/nano-electromechanical systems. This work evaluates the feasibility of using the protic ionic liquids [4-picH][HSO4], [4-picH][CH3SO3], [MIMH][HSO4], and [MIMH][CH3SO3] and the aprotic ILs [C6mim][HSO4] and [C6mim][CH3SO3] as additives to model lubricant poly(ethylene glycol) (PEG200) to lubricate silicon surfaces. Additives based on the cation [4-picH]+ exhibited the best tribological performance, with the optimal value for 2% [4-picH][HSO4] in PEG200 (w/w). Molecular dynamics (MD) simulations of the first stages of adsorption of the ILs at the glass surface were performed to portray the molecular behavior of the ILs added to PEG200 and their interaction with the silica substrate. For the pure ILs at the solid substrates, the MD results indicated that weak specific interactions of the cation with the glass interface are lost to accommodate the larger anion in the first contact layer. For the PEG200 + 2% [4-picH][HSO4] system, the formation of a more compact protective film adsorbed at the glass surface is revealed by a larger trans population of the dihedral angle -O(R)-C-C-O(R)- in PEG200, in comparison to the same distribution for the pure model lubricant. Our findings suggest that the enhanced lubrication performance of PEG200 with [4-picH][HSO4] arises from synergistic interactions between the protic IL and PEG200 at the adsorbed layer.publishersversionpublishe

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

The importance of being flexible: structural properties of ionic liquids from a molecular perspective

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Nanostructural organization in ionic liquids

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