Ok this is my first$^*$ question on overflow, my apologies if this is not the right place to ask what follows!
I observed the following phenomenon: I put a (vitamin) tablet into water, then after a while a thin film forms (I have attached a picture of it). That made me wonder - is there a particular pde that models such a process (or particular stages of it)? I realize that this phenomenon is quite complex, but perhaps there are particular stages that can be modelled and studied generically (for example I think soap bubbles are studied mathematically). What interests me in particular is the transition from the stage where there is only the surface of the water to the stage where a second film has formed.
Here is the picture:
Thanks very much for pointers to sources where I can learn more.
$^*$(Edit: I just realised it is in fact my second question here)