Dynamics of polydisperse hard-spheres under strong confinement

Abstract

We use molecular simulation to probe the connection between local structure and the unusual re-entrant dynamics observed for polydisperse hard-sphere liquids confined in thin slit pores. The local structure is characterised by calculating 2-D bond-orientational order parameters associated with square and hexatic order for particles in the layer adjacent to the confining walls. When the wall separation is commensurate with the average particle size, the particles primarily exhibit local hexatic order, whereas local square order increases in prevalence for incommensurate geometries. The relaxation time extracted from the ensemble-averaged mean-square displacement increases exponentially with the static correlation length associated with hexatic local order in strongly confined commensurate geometries, in agreement with theoretical predictions for dynamical slowing. Square order, by contrast, is not associated with a growing length scale for either commensurate or incommensurate geometries, indicating that it is strongly geometrically frustrated. Our results suggest that the influence of bond-orientational order on dynamical slowing may be altered by changing the extent of confinement.

GRAPHICAL ABSTRACT

Keywords:

• Glass transition
• molecular dynamics
• confinement
• hard spheres
• correlation length

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Acknowledgements

This work was completed in part with resources provided by the Research Computing Data Core at the University of Houston.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors acknowledge support from the Welch Foundation (E-1869 to J.C.C. and E-1882 to J.C.P.) and the National Science Foundation (CBET-1705968).