Research Publications People Computers

Christopher Pooley


My work involves both numerical simulations and theoretical understanding of a wide range of topics within the field of complex fluids.

1. Recently we have been studying the effect of thermal gradients on binary systems.

This film illustrates the pattern formation which occurs when a binary fluid is convected between two plates. The critical transition temperature Tc (below which the fluid binary phase separates) is between the temperature of the lower hot plate and upper cold plate.

This shows cooling the lower edge of the sample below Tc and having the white component lighter than the black. This results in plumes of white fluid rising driven by buoyancy.

2. In studying a system which consists of a binary fluid in coexistence with it homogeneous vapor we discovered an interesting nucleated growth mechanism. The system is initially almost uniform, and is cooled between the liquid gas coexistence curve but outside of the spinodal curve, such that the system does not undergo spinodal decomposition. A nucleated region is placed at the center and strange tentacle patterns are develop as the fluid phase separates. We do not fully understand how these form, but suspect that it is a result of an interesting interplay between fluid flow and diffusion of the two binary species.

3. We have constructed a simple model of surfactant self assembly.
Our aim is to be able to understand the processes involved in a new experimental technique called evaporation induced self assembly, which is used to construct very well defined nanoscopic coatings on material surfaces. Hopefully this understanding will lead to improved manufacture and quality of process.

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This shows the formation of close packed micelles. The surfactant molecules are modeled by a hydrophilic head group (light gray) attached to a chain of black beads, which model the hydrophobic tail. The small dark gray circles are solvent particles. All particles collide with a hard sphere interaction, but with the collision parameter not necessarily the sum of the two colliding particle radii. For instance the solvent-tail radius of interaction is larger than would be expected, to take account of the repulsive potential acting between the species. Since this model contains no explicit potentials (energy is exactly conserved) it can be run much fasted than a corresponding molecular dynamics simulation. Hopefully this will allow simulation timescales to be sufficiently long to also exhibit hydrodynamic flow.

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By changing the shape of the surfactant different structures may be observed. This example shows rod like molecules resulting in lamella structures near to a wall (for clarity the fluid particles are not shown).

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