History-Dependent Stress Relaxation of Liquids under High-Confinement: A Molecular Dynamics Study

Gao, Hongyu

doi:10.3390/lubricants10020015

Cited by 2 publications

(1 citation statement)

References 53 publications

(87 reference statements)

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“…Molecular dynamics (MD) simulation is a powerful tool which can be used to obtain microscopic insights into the properties of confined liquids behind the experimental results and to guide future research applications. Several studies have been conducted using both equilibrium and non-equilibrium MD simulations on confined liquids such as Lennard-Jones (LJ) particles [22][23][24] , water 11,14,25,26 , and hydrocarbons [27][28][29] . A recent simulation conducted by Ta et al 27 of a hexadecane film confined between iron oxide surfaces demonstrated that an increase in the shear rate can result in a decrease in the degree of ordering of the hexadecane film and an increase in the velocity slip at the solid-liquid interfaces.…”

Section: Introductionmentioning

confidence: 99%

Correlation between ordering and shear thinning in confined liquids

Kobayashi¹,

Arai²,

Yasuoka³

2022

Preprint

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Despite the extensive research that has been conducted for decades on the behavior of confined liquids, detailed knowledge of this phenomenon, particularly in the mixed/boundary lubrication regime, remains limited. This can be attributed to several factors including the difficulty of direct experimental observations of the behavior of lubricant molecules under non-equilibrium conditions, the high computational cost of molecular simulations to reach steady state, and the low signal-to-noise ratio at extremely low shear rates corresponding to actual operating conditions. To this end, we studied the correlation between the structure formation and shear viscosity of octamethylcyclotetrasiloxane confined between two mica surfaces in a mixed/boundary lubrication regime. Three different surface separations corresponding to two-, three-, and five-layered structures were considered to analyze the effect of confinement. The orientational distributions with one specific peak for n = 2 and two distributions, including a parallel orientation with the surface normal for n > 2, were observed at rest. The confined liquids exhibited a distinct shear-thinning behavior independent of surface separations for a relatively low sliding velocity, V x 10 −1 m/s. However, the shear viscosities at V x 10 −1 m/s depended on the number of layered structures. Newtonian behavior was observed with a further increase in the sliding velocity. Furthermore, we found a strong correlation between the degree of molecular orientation and the shear viscosity of the confined liquids. The magnitude of the shear viscosity of the confined liquids can primarily be determined by the degree of molecular orientation, and shear-thinning originates from the vanishing of specific orientational distributions with increasing sliding velocity.

show abstract

Section: Introductionmentioning

confidence: 99%

Correlation between ordering and shear thinning in confined liquids

Kobayashi¹,

Arai²,

Yasuoka³

2022

Preprint

View full text Add to dashboard Cite

show abstract

Correlation between ordering and shear thinning in confined OMCTS liquids

Kobayashi

Arai

Yasuoka

2022

The Journal of Chemical Physics

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Despite the extensive research that has been conducted for decades on the behavior of confined liquids, detailed knowledge of this phenomenon, particularly in the mixed/boundary lubrication regime, remains limited. This can be attributed to several factors including the difficulty of direct experimental observations of the behavior of lubricant molecules under non-equilibrium conditions, the high computational cost of molecular simulations to reach steady state, and the low signal-to-noise ratio at extremely low shear rates corresponding to actual operating conditions. To this end, we studied the correlation between the structure formation and shear viscosity of octamethylcyclotetrasiloxane confined between two mica surfaces in a mixed/boundary lubrication regime. Three different surface separations corresponding to two-, three-, and five-layered structures were considered to analyze the effect of confinement. The orientational distributions with one specific peak for n=2 and two distributions, including a parallel orientation with the surface normal for n>2, were observed at rest. The confined liquids exhibited a distinct shear-thinning behavior independent of surface separations for a relatively low shear rate, \dot{\gamma}<10^{8} s^{-1}. However, the shear viscosities at \dot{\gamma}<10^{8} s^{-1} depended on the number of layered structures. Newtonian behavior was observed with a further increase in the shear rate. Furthermore, we found a strong correlation between the degree of molecular orientation and the shear viscosity of the confined liquids. The magnitude of the shear viscosity of the confined liquids can primarily be determined by the degree of molecular orientation, and shear-thinning originates from the vanishing of specific orientational distributions with increasing shear rate.

show abstract

History-Dependent Stress Relaxation of Liquids under High-Confinement: A Molecular Dynamics Study

Cited by 2 publications

References 53 publications

Correlation between ordering and shear thinning in confined liquids

Correlation between ordering and shear thinning in confined liquids

Correlation between ordering and shear thinning in confined OMCTS liquids

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