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Particles trapped at fluid interfaces

Shenghan Yan

MIT Class of 2007
B.S. Chemical Engineering
B.S. Economics

The goal of my project is to investigate the collective dynamic behavior of colloidal particles trapped in a fluid interface, which is effectively a two-dimensional colloidal suspension. Although many interesting observations were reported, there has not been a comprehensible theoretical interpretation of the system, particularly of the capillary attraction caused by electrostatic effect of charged particles. We started by following the theory proposed by Nicolaides and Kralchevsky on the electrodipping effect and interfacial deformation. Video microscopy and Monte Carlo simulation with pair wise interactions were used to analyze the behavior of the particles at interface. Our current analysis, based on both experiments and simulation, has shown that as surface concentration increases, the system of micron-sized particles trapped at a water/decane interface undergoes phase transition from a gas phase to an isotropic liquid phase and eventually achieves a solid state. However, irregular domains with different particle concentrations were observed on the water/air interface, which are still under investigation.

Particles on the water/air interface forming circular structures.

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