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Journal of Chemical Physics / Volume 107 / Issue 23

J. Chem. Phys. 107, 10335 (1997); http://dx.doi.org/10.1063/1.474173 (9 pages)

Shear behavior of squalane and tetracosane under extreme confinement. III. Effect of confinement on viscosity

S. A. Gupta1,2, H. D. Cochran1,2, and P. T. Cummings1,2

1Department of Chemical Engineering, University of Tennessee, Knoxville, Tennessee 37996-2200
2Chemical Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6268

(Received 9 June 1997; accepted 11 September 1997)

This study uses nonequilibrium molecular dynamics simulation to explore the rheology of confined liquid alkanes. Two alkanes that differ in molecular structural complexity are examined: tetracosane (C24H50), which is a linear alkane, and squalane (C30H62), which has six symmetrically placed methyl branches along a 24 carbon backbone. These model lubricants are confined between model walls that have short chains tethered to them, thus screening the wall details. This paper, the third of a three part series, compares the viscosities of the confined fluids to those of the bulk fluids. The alkanes are described by a well-documented potential model that has been shown to reproduce bulk experimental viscosity and phase equilibria measurements. Details of the simulation method, and structural information can be found in the preceding two papers of this series. The measured strain rates in these simulations range between 108 and 1011 s−1, which is typical of a number of practical applications. The confined fluids undergo extensive shear thinning, showing a power-law behavior. Comparison of results for the confined fluid to those for the bulk fluid reveal that, for the conditions examined, there is no difference between the bulk and confined viscosities for these alkanes. This observation is in contrast to experimental results at much lower strain rates (10–105 s−1), which indicate the viscosities of the confined fluid to be much larger than the bulk viscosities. In making the comparison, we have carefully accounted for slip at the wall and have performed simulations of the bulk fluid at the same conditions of strain rate, temperature, and pressure as for the corresponding confined fluid. The viscosity is found to be independent of the wall spacing. The calculated power-law exponents are similar to experimentally observed values. We also note that the exponent increases with increasing density of the fluid. © 1997 American Institute of Physics.

© 1997 American Institute of Physics

EDITORIALLY RELATED

    Related Articles

  1. Shear behavior of squalane and tetracosane under extreme confinement. I. Model, simulation method, and interfacial slip
    S. A. Gupta et al.
    J. Chem. Phys. 107, 10316 (1997)JCPSA6000107000023010316000001
  2. Shear behavior of squalane and tetracosane under extreme confinement. II. Confined film structure
    S. A. Gupta et al.
    J. Chem. Phys. 107, 10327 (1997)JCPSA6000107000023010327000001

RELATED DATABASES

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KEYWORDS and PACS

Keywords

flow simulation, liquid films, LUBRICANTS, SHEAR PROPERTIES, SQUALANE, ALKANES, VISCOSITY, DENSITY, SLIP FLOW, RHEOLOGY, MOLECULAR DYNAMICS METHOD, SIMULATION, THIN FILMS, LIQUIDS

PACS

  • 66.20.-d

    Viscosity of liquids; diffusive momentum transport

  • 83.50.Lh

    Slip boundary effects (interfacial and free surface flows)

  • 61.20.Ja

    Computer simulation of liquid structure

  • 83.50.Ax

    Steady shear flows, viscometric flow

  • 83.10.Bb

    Kinematics of deformation and flow

  • 47.11.-j

    Computational methods in fluid dynamics

  • 83.10.Rs

    Computer simulation of molecular and particle dynamics

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.474173

PUBLICATION DATA

ISSN

0021-9606 (print)  
1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
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