Choe, Eunju Julia (2017) Molecular dynamics study of rheological properties of liquid alkanes under high pressure and shear. PhD thesis, University of Warwick.

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Abstract

In this study, molecular dynamics (MD) simulations have been performed to study rheological properties of liquid alkanes under a range of pressures up to several GPa and high shear rates. The liquid alkane considered in this study is 2,4- dicyclohexyl-2-methylpentane (DCMP), which is a highly viscous fluid. Two further molecular motifs, octadecane (Linear) and 1,6-dicyclohexyl-hexane (Dumb- bell) were chosen as comparison. The rheological properties of DCMP under high pressure were studied using molecular dynamics simulations. A wide range of pressure (1 atm ≤ P ≤ 10 000 atm) and shear (5.47 x 10 7 s-1 ≤ y ≤ 5.47 x 10 11 s-1) conditions have been considered. Simulation parameters have been carefully chosen from preliminary simulations. MD allows access to understanding not always available experimentally.

The present simulation results confirm that the density of all three motifs increase as pressure increases. The results also show that the mean squared dis- placements of molecules decrease as pressure increases. At pressures higher than 3000 atm, the movement almost ceases for DCMP and Dumbbell implying a solid- like behaviour at very high pressures. The viscosity of DCMP is higher than that of Dumbbell, but comparable to Linear. As molecules tend to adopt compact shapes at high pressures, this affects their rheological properties accordingly. The viscosity of Dumbbell is found to be the lowest among the three. Viscosities in- crease with pressure for all three molecules with larger changes with DCMP and Linear.

It is found that the pressure of the systems increase when the shear is applied. The viscosity of DCMP and Dumbbell increase as pressure increases. The viscosity of DCMP is found to be higher than that of Dumbbell, especially in the high pressure region. DCMP and Dumbbell show the shear thinning behaviour. The start of a plateau is observed for DCMP and the viscosity in the plateau is at the same order of magnitude as the zero shear viscosity estimated from the Stokes-Einstein relation for low pressure systems.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Rheology -- Simulation methods, Alkanes, Molecular dynamics
Official Date:	September 2017
Dates:	Date Event September 2017 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Rodger, P. M. (P. Mark)
Extent:	xxvii, 183 leaves : illustrations, charts.
Language:	eng

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