Computer simulations of branched alkanes: The effect of side chain and its position on rheological behavior

Lahtela, Maija; Linnolahti, Mikko; Pakkanen, Tapani A.; Rowley, Richard L.

doi:10.1063/1.475649

Cited by 20 publications

(13 citation statements)

References 29 publications

(29 reference statements)

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“…In contrast, branching in the alkyl chains has not been extensively exploited as a means of systematically varying the physicochemical properties of ILs. Indeed, it is well-known that branching decreases the boiling and melting points and increases the viscosities − of alkanes. Andresova et al recently examined the effect of branched and cyclic alkyl groups on the physicochemical properties of imidazolium-based ILs and found that the viscosities of the branched and cyclic ILs are greater than those of the analogous linear ILs.…”

Section: Introductionmentioning

confidence: 99%

Effect of Alkyl Chain Branching on Physicochemical Properties of Imidazolium-Based Ionic Liquids

et al. 2016

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The branched ionic liquids (ILs) 1-(iso-alkyl)-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([(N – 2)mC N‑1C1im][NTf2] with N = 3–7) were synthesized and their physicochemical properties characterized and compared with the properties of linear ILs 1-(n-alkyl)-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([C N C1im][NTf2] with N = 3–7). For N = 4–7, the density of the branched IL [(N – 2)mC N–1C1im][NTf2] is the same as that of its linear analogue [C N C1im][NTf2] within the standard uncertainty of the measurements. In the case of the N = 3 [1mC2C1im][NTf2]/[C3C1im][NTf2] pair, the density of the branched IL is 0.13% higher than that of the linear IL. For a branched/linear IL pair with a given N, the glass transition temperature T g, melting temperature T m, and viscosity η are higher for the branched IL than for the linear IL. [2mC3C1im][NTf2] is an exception in that its T m is lower than that of [C4C1im][NTf2]. Moreover, the viscosity of [2mC3C1im][NTf2] is anomalously higher than what would be predicted based on the trend of the other branched ILs. These trends in the viscosities of the linear and branched ILs are consistent with recent molecular dynamics simulations. Thermal gravimetric analysis indicates that linear ILs are thermally more stable than branched ILs. Pulsed-gradient spin–echo (PGSE) NMR diffusion measurements show that the self-diffusion coefficients of the ions vary inversely with the viscosities according to the Stokes–Einstein (SE) equation. The hydrodynamic radii of the cations and anions of linear ILs calculated from the SE equation however are consistently higher than those of the corresponding branched ILs.

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Section: Introductionmentioning

confidence: 99%

Effect of Alkyl Chain Branching on Physicochemical Properties of Imidazolium-Based Ionic Liquids

et al. 2016

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“…So far, only a few studies have used NEMD to investigate the effect of branching on the rheology of alkanes of intermediate size. [11][12][13][14][15][16] Utilizing a united atom model for alkanes 5,17 and rRESPA multi-time-step dynamics 6,18,19 incorporating a Nosé thermostat, we present the results of equilibrium ͑EMD͒ and nonequilibrium molecular dynamics simulations of three isomers of C 30 H 62 : n-triacontane, 9-n-octyldocosane, and squalane ͑the architectures of the branched molecules are illustrated in Fig. 1͒.…”

Section: Introductionmentioning

confidence: 99%

Rheology of lubricant basestocks: A molecular dynamics study of C30 isomers

Moore

Cui

Cochran

et al. 2000

The Journal of Chemical Physics

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Rheological and structural studies of liquid decane, hexadecane, and tetracosane under planar elongational flow using nonequilibrium molecular-dynamics simulations Concentration effects on lubrication rheology for polymer solution in molecularly thin film using molecular dynamics J. Appl. Phys. 95, 8450 (2004); 10.1063/1.1751629 Molecular dynamics study of the nano-rheology of n-dodecane confined between planar surfaces Rheological, thermodynamic, and structural studies of linear and branched alkanes under shearWe have performed extensive equilibrium and nonequilibrium molecular dynamics ͑EMD and NEMD͒ simulations of three isomers of C 30 H 62 at temperatures of 311 and 372 K employing a united atom model. Using the rotational relaxation time calculated from the EMD simulation, the Rouse model predicts a zero-shear viscosity for n-triacontane within 16% of the value determined by NEMD. Compared to experiment, NEMD and the united atom model underpredict the kinematic viscosities of n-triacontane and 9-n-octyldocosane but accurately predict the values for squalane ͑within 15%͒. In addition, the predicted values of the kinematic viscosity index for both 9-n-octyldocosane and squalane are in quantitative agreement with experiment and represent the first such predictions by molecular simulation. This same general potential model and computational approach can be used to predict this important lubricant property for potential lubricants prior to their synthesis, offering the possibility of simulation-guided lubricant design.

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“…Most of these works have focused on linear alkanes. A smaller number of studies have been conducted on branched species. − To our knowledge, only one group has performed molecular simulations on realistic PAO molecules. , This work, however, was focused on the conformational properties of typical PAO molecules and no viscosity computations were performed. Recently, the same group performed nonequilibrium molecular dynamics (NEMD) simulations on eicosane isomers to study the effect of side chains on fluid rheology .…”

Section: Introductionmentioning

confidence: 99%

Molecular Simulation of Poly-α-olefin Synthetic Lubricants: Impact of Molecular Architecture on Performance Properties

and

Maginn

1999

J. Phys. Chem. B

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Equilibrium and nonequilibrium molecular dynamics simulations are performed at constant pressure and temperature on three structurally distinct poly-R-olefin (PAO) isomers representative of a major component in synthetic motor oil basestock. In agreement with empirical observations, the temperature dependence of viscosity, as characterized by the viscosity number (VN), is reduced as the degree of branching is lowered. A molecular-level explanation for this behavior is given in terms of the energy barriers for intramolecular reorientation. Other dynamic properties, such as the diffusivity and rate of tumbling, were also computed and found to have similar dependencies on temperature as the viscosity. Based on these calculations, it appears that PAO molecules with long, widely spaced branches should yield a higher VN than those with short, closely spaced branches. The impact of shear rate on PAO properties is also investigated. High shear rates and shear-thinning increases the VN because the behavior of the fluid is largely dominated by the flow field rather than by the thermodynamic state point. Contrary to what has been observed with linear alkanes, it is observed that molecular alignment with the flow field does not always correlate with enhanced shear-thinning. These observations are explained in terms of a competition between the shear forces responsible for aligning the molecules and intermolecular forces that resist shear-thinning. The results of the present work provide molecular-level explanations for the favorable lubricant properties exhibited by "star-like" molecules and suggest an important strategy for assisting in a more rational approach toward the development of improved lubricants and additives.

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Computer simulations of branched alkanes: The effect of side chain and its position on rheological behavior

Cited by 20 publications

References 29 publications

Effect of Alkyl Chain Branching on Physicochemical Properties of Imidazolium-Based Ionic Liquids

Effect of Alkyl Chain Branching on Physicochemical Properties of Imidazolium-Based Ionic Liquids

Rheology of lubricant basestocks: A molecular dynamics study of C30 isomers

Molecular Simulation of Poly-α-olefin Synthetic Lubricants: Impact of Molecular Architecture on Performance Properties

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