Freezing of a soft-core fluid in a one-dimensional potential: appearance of a locked smectic phase

ABSTRACT

We investigate the phase behaviour of a two-dimensional colloidal model system of ultra-soft particles on a substrate which varies periodically along one spatial direction. Our calculations are based on mean-field density functional theory for a system of particles interacting via an ultra-soft potential, that is, the generalised exponential model with index four (GEM-4). For suitable substrate periodicities (with commensurability parameter p = 2), we find a succession of phase transitions from a modulated liquid to a locked smectic and then to a locked floating solid phase. The appearance of a locked smectic phase is consistent with earlier theoretical predictions and experiments for freezing of more repulsive systems on structured surfaces (with p = 2). However, the present ultra-soft system does not display re-entrant melting. We here investigate the details of the density distributions of the different phases, thereby supplementing earlier work on GEM-4 systems with p = 1 [Phys. Rev. E 101, 012609 (2020)]. Interestingly, the observed succession of phase transitions can be triggered through different paths along which physical control parameters are changed.

GRAPHICAL ABSTRACT

Keywords:

• Ultra-soft particles
• periodic substrate
• freezing
• density functional theory
• mean-field approximation

Acknowledgements

S.H.L.K. would like to thank Gerhard Findenegg for many enjoyable discussions and collaboration within the DFG-funded Collaborative Research Center 448 ‘Mesoscopically structured composites’ and the International Research Training Group 1524 ‘Self-assembled soft matter nanostructure at interfaces’.

Disclosure statement

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