Adam Law

Soft Matter Theory

Colloids are small particles that are dispersed in liquid or gas and their size usually ranges from nanometres to tens of micrometres [1]. The last two decades has witnessed an increasing interest into the investigation of colloids because they are abundant in everyday experience. From mayonnaise to blood and from ink to smoke, they are labelled under the banner of soft matter, which generally covers physical states that are easily deformed by thermal stresses or thermal fluctuations and occur at an energy scale comparable with room temperature thermal energy. Generally, it is what we are made of and what we use in countless industrial applications in the chemical, pharmaceutical and food industries. It is however when focussing at an interface between two substances where colloids exhibit interesting features.

Alternatively, colloids are an interesting model system for atoms. Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy. Many of the forces that govern the structure and behaviour of matter, such as excluded volume interactions or electrostatic forces also govern the structure and behaviour of colloids. The properties of colloidal monolayers is determined by the interaction forces between colloidal particles, however describing the forces determining the physical behaviour of colloids at interfaces still remains a problem in the modern theory of colloid interaction due to the inclusion of the interface where the particles lie. In order to determine the actual nature of these forces, it is important to be able to measure these forces accurately.

My current theme of research investigates a number of interesting questions associated with colloids. One of these is to look into the so called Critical Casimir Effect, a thermodynamic analog of the famed quantum mechanical effect. When soft matter systems approach it's critical point, long ranged fluctuations appear that can induce further interactions between colloids. This is a big research topic in my current group and has been deduced theoretically and investigated experimentally for various geometries. It is hoped that my knowledge of fluid interfaces within the bounds of colloidal interactions can provide more knowledge into these Casimir forces when near fluid interfaces.

My other research involves particles trapped at fluid interfaces. I am particularly interested in using Integral Equation Theory to use structural data to extract effective pair potentials between particles within monodisperse systems. Initially this has been put into use on simulations of particles at fluid interfaces but now we are seeking to expand this to experiments, those of course with good enough statistics of probability distributions for these types of systems.

In addition, I am interested in the formation of colloidal crystals, in particular binary colloidal systems. Through theory and simulations we have investigated the formation of binary colloidal crystals, for particles adsorbed to a oil/water interface. Through the very strong long ranged interactions between the particles, we witness for the first time, particles stabilised at long range which then form two-dimensional super lattice structures.

These current themes of research require me to make extensive use of simulation techniques such as Monte Carlo and Molecular Dynamic methods. My toolset includes a variety of programming languages such as C++, Fortran and Mathematica.

[1] B.P. Binks and T.S. Horozov. Colloidal Particles at Liquid Interfaces, chapter 1, pages 1-74. Cambridge University Press, Cambridge, 2006.