Re: Physics in a toilet bawl

[LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>]

Several days ago Brian Whatcott gave a reference which I found and read.
The authors watched very small balls (diameters 10 nm) suspended in water. 
The density of balls was about the same as water and their distribution
in space was found to be uniform. Then ten times larger balls (about 10% 
of the total number of balls) were added. Over a period of tens of hours
a distribution which was originally uniform was found to be strongly 
non-uniform. It showes crystal-like patterns. What kind of force is 
involved? The answer given makes sense to me; it can explain the behaviour 
of hair whiskers.

Thanks Brian for reporting this article ("The Sciences" May-June 1997). 
Ludwik Kowalski

> As it turns out, there is a recent effort to understand the apparently
> anti-entropic clustering of small mobile objects in a suspension.
>
> The collaboration from UPenn, UCSB, URochester NY, found that that
> small polystyrene balls in water do not cluster when the balls have
>  constant size. If a few balls of larger diameter are added, these 
> latter start clustering at the edges in flat lozenges and hexagons.

M.A.Santos responded:

> Are u talking about colloid like sized balls? Isn't there a great
> difference with respect to someones' hair? Indeed, the aggregation
> of micelles of surfactant is also apparently anti-entropic, but
> the hydrophobic effect seems to explain it: size aside, I'm not
> sure to see all the differences.

        I do not know; it was just a casual observation. L.K.