Diffusion Constant: Increase/Decrease in Time & Length?

[retroscience]

a theoretical qstn..

the diffusion constant D, represents the avg. rate of unit displacement by a fluid particle.

should D increase or decrease in time?
and
should D increase or decrease if length (lets say length of the capillary through with its travelling) increases?

- m

 

[mathman]

The diffusion constant depends on the state of the medium. Whether or how it changes depends on the changes in the medium. Time is only relevant if the medium changes in time.