Area dependence of the surface tension of a Lennard‐Jones fluid from molecular dynamics simulations

1995 ◽  
Vol 103 (23) ◽  
pp. 10214-10216 ◽  
Author(s):  
Li‐Jen Chen
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Molecular Dynamics Simulations ◽  
Lennard Jones ◽  
Dynamics Simulations

scholarly journals Shear-rate dependence of thermodynamic properties of the Lennard-Jones truncated and shifted fluid by molecular dynamics simulations

2021 ◽  
Author(s):  
Martin P. Lautenschlaeger ◽  
Hans Hasse
Keyword(s):  
Molecular Dynamics ◽  
Shear Stress ◽  
Shear Rate ◽  
Molecular Dynamics Simulations ◽  
Local Structure ◽  
Rate Dependence ◽  
Lennard Jones ◽  
Fluid Properties ◽  
Dynamics Simulations ◽  
Shear Rate Dependence

It was shown recently that using the two-gradient method, thermal, caloric, and transport properties of fluids under quasi-equilibrium conditions can be determined simultaneously from nonequilibrium molecular dynamics simulations. It is shown here that the influence of shear stresses on these properties can also be studied using the same method. The studied fluid is described by the Lennard-Jones truncated and shifted potential with the cut-off radius r*c = 2.5σ. For a given temperature T and density ρ, the influence of the shear rate on the following fluid properties is determined: pressure p, internal energy u, enthalpy h, isobaric heat capacity cp, thermal expansion coefficient αp, shear viscosity η, and self-diffusion coefficient D. Data for 27 state points in the range of T ∈ [0.7, 8.0] and ρ ∈ [0.3, 1.0] are reported for five different shear rates (γ ̇ ∈ [0.1,1.0]). Correlations for all properties are provided and compared with literature data. An influence of the shear stress on the fluid properties was found only for states with low temperature and high density. The shear-rate dependence is caused by changes in the local structure of the fluid which were also investigated in the present work. A criterion for identifying the regions in which a given shear stress has an influence on the fluid properties was developed. It is based on information on the local structure of the fluid. For the self-diffusivity, shear-induced anisotropic effects were observed and are discussed.

scholarly journals Interface Characteristics of Neat Melts and Binary Mixtures of Polyethylenes from Atomistic Molecular Dynamics Simulations

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1059
Author(s):  
Sanghun Lee ◽  
Curtis W. Frank ◽  
Do Y. Yoon
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Molecular Dynamics Simulations ◽  
Binary Mixtures ◽  
Surface Segregation ◽  
Surface Region ◽  
Polymer Chains ◽  
Methyl Groups ◽  
Free Standing ◽  
Dynamics Simulations

Molecular dynamics simulations of free-standing thin films of neat melts of polyethylene (PE) chains up to C150H302 and their binary mixtures with n-C13H28 are performed employing a united atom model. We estimate the surface tension values of PE melts from the atomic virial tensor over a range of temperatures, which are in good agreement with experimental results. Compared with short n-alkane systems, there is an enhanced surface segregation of methyl chain ends in longer PE chains. Moreover, the methyl groups become more segregated in the surface region with decreasing temperature, leading to the conclusion that the surface-segregation of methyl chain ends mainly arises from the enthalpic origin attributed to the lower cohesive energy density of terminal methyl groups. In the mixtures of two different chain lengths, the shorter chains are more likely to be found in the surface region, and this molecular segregation in moderately asymmetric mixtures in the chain length (C13H28 + C44H90) is dominated by the enthalpic effect of methyl chain ends. Such molecular segregation is further enhanced and dominated by the entropic effect of conformational constraints in the surface for the highly asymmetric mixtures containing long polymer chains (C13H28 + C150H3020). The estimated surface tension values of the mixtures are consistent with the observed molecular segregation characteristics. Despite this molecular segregation, the normalized density of methyl chain ends of the longer chain is more strongly enhanced, as compared with the all-segment density of the longer chain itself, in the surface region of melt mixtures. In addition, the molecular segregation results in higher order parameter of the shorter-chain segments at the surface and deeper persistence of surface-induced segmental order into the film for the longer chains, as compared with those in neat melt films.

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