# Difference between revisions of "Particle rafts"

Particles at an interface between two fluids often coalesce and build a densely packed monolayer. The most common example for this is hydrophobic particles at an air-water interface (e.g. tea particles swimming on top of a cup). They are similar to the much better known bubble rafts.

In many respects, this layer of particles behaves like a linear elastic 2D structure. One example of this kind of behavior is out of plane buckling under compression (described in detail here), where the particle raft exhibits a shear modulus of

$G \approx \frac{\gamma}{d}$

where $\gamma$ is the surface tension and d is the single particle diameter.

This ability to sustain shear stresses, suggests that high stresses beyond the linear regime might be sustained by fractures in the structure. One option to induce fractures is the addition of surfactants directly on the monolayer (e.g. putting milk on the tea particles in the tea). Experimental results (in detail here) show that the system reacts with a very complex behavior, including crack branching, kinking and frustrated side branches.

The behavior of particle rafts, especially their interaction with surfactants is important to many applications where bubbles or drops (which are often coated with small particles) play a role. A prime example is drug delivery by inhalation as detailed here