Crystallisation of soft matter under confinement at interfaces and in wedges
Andrew Archer
Alexandr Malijevsky
2134/20470
https://repository.lboro.ac.uk/articles/journal_contribution/Crystallisation_of_soft_matter_under_confinement_at_interfaces_and_in_wedges/9388364
The surface freezing and surface melting transitions that are exhibited by a model two-dimensional
soft matter system is studied. The behaviour when con ned within a wedge is also considered. The
system consists of particles interacting via a soft purely repulsive pair potential. Density functional
theory (DFT) is used to calculate density pro les and thermodynamic quantities. The external
potential due to the con ning walls is modelled via a hard-wall with an additional repulsive Yukawa
potential. The surface phase behaviour depends on the range and strength of this repulsion: When
the repulsion strength is weak, the wall promotes freezing at the surface of the wall. The thickness of
this frozen layer grows logarithmically as the bulk liquid-solid phase coexistence is approached. Our
mean- eld DFT predicts that this crystalline layer at the wall must be nucleated (i.e. there is a free
energy barrier) and its formation is necessarily a rst-order transition, referred to as `prefreezing',
by analogy with the prewetting transition. However, in contrast to the latter, prefreezing cannot
terminate in a critical point, since the phase transition involves a change in symmetry. If the wall-
uid interaction is su ciently long ranged and the repulsion is strong enough, surface melting can
instead occur. Then the interface between the wall and the bulk crystalline solid becomes wet by
the liquid phase as the chemical potential is decreased towards the value at liquid-solid coexistence.
It is observed that the nite thickness
uid lm at the wall has a broken translational symmetry due
to its proximity to the bulk crystal and so the nucleation of the wetting lm can be either rst-order
or continuous. Our mean- eld theory predicts that for certain wall potentials there is a premelting
critical point analogous to the surface critical point for the prewetting transition. When the
uid
is con ned within a linear wedge, this can strongly promote freezing when the opening angle of the
wedge is commensurate with the crystal lattice.
2016-03-04 12:22:56
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Mathematical Sciences not elsewhere classified
Condensed Matter Physics