For some time it was believed that simple, single - component, fluid phase behaviour was limited to a homogeneous gas and homogeneous liquid phase separated by a line of first order phase transitions. However, recent studies have demonstrated that simple fluid behaviour can be extended to richer phase diagrams through tuning of the effective potential.Fluids whose constituent particles feel a strong attraction at close range and weak repulsion at longer ranges have been shown, under certain conditions, to assemble into heterogeneous structures such as spherical and cylindrical clusters, lamellae and spherical and cylindrical voids.Lattice Monte Carlo simulations are used to explore the phase diagram of a single - component fluid following a hard - core effective potential with an attractive and a repulsive Yukawa tail. The relative strngths of attractive and repulsive potentials are found for which heterogeneous structures become stable. Then the region of stability of heterogeneous structures is delimited through the use of histogram reweighting to map out the locus of points at which the homogeneous and heterogeneous states have equal free energy. A transition matrix Monte Carlo biasing technique is used to reveal the system behaviour inside the free energy barrier at low temperatures, when the gas - liquid phase transition appears to have re-asserted itself. Finally, a discussion as to the mechanism for assembly of the heterogeneous structures is offered.
|Date of Award||13 Sep 2016|
|Supervisor||Nigel Wilding (Supervisor)|
- Monte Carlo
- Transition Matrix