Diffusion: Heterogeneous mixtures
Download model  (right click to save)
This model was created to simulate the behavior of a heterogenous mixture of particles (oil and water) each of whose random motion is influenced by interactions with other particles. This is in contrast to the behavior of randomly moving particles in the absence of interactions (see From Random Motion to Order: Diffusion and Some Of It's Implications ). As a result of the interactions, particles in this case do not end up randomly distributed in space but rather tend to cluster with particles like themselves.
How it works
At each iteration, each particle looks at the area around itself (set by the "radius" slider). If there are more particles of it's own kind, it moves in a random direction a small distance (set by the "small-jump" slider). If there are more particles of the other kind, it moves in a random direction a larger distance (set by the "big-jump" slider).
How to use it
Click on "add water particles" and "add oil particles" to create a mixture. The number of particles added can be changed with the "number" slider.
You can move particles by clicking on "move-particle" and then clicking on a particle and dragging it with your mouse. You can track a particle by right clicking on it and selecting "watch" from the "particle #" menu at the bottom. To go back to the normal view, right click anywhere and select "reset-perspective".
Things to notice
Notice that if small-jump and big-jump have the same value, then the particles do not separate. This is equivilent to there being no interaction between the particles (see From Random Motion to Order: Diffusion and Some Of It's Implications ).
Notice also that if both small- and big-jump sliders are set to 0, no separate occurs. Separation depends not only on interaction but also on random motion influenced by those interactions.
Things to try
How does changing the jump and radius distances affect whether or not the particles separate? the rate at which they separate? the average ratio at which the mixture stabilizes?
Posted by Laura Cyckowski and Paul Grobstein October 2010. Applet created using NetLogo , the availability of which is gratefully acknowledged.