(67a) Effect of Wall Hinderence on Brownian Motion and Mobility

As the 80^th anniversary of Ruckenstein's birth,
2005 is also the 100^th anniversary of Einstein's first paper on
Brownian motion [Annalen der Physik 19, 549 (1905)] in which Einstein
observed that Avogadro's number N could be deduced by measuring
independently the mobility m and diffusion coefficient D of microscopic
Brownian particles.  In particular, he predicted that the two were related by D = mRT/N, where R is the
universal gas constant and T is absolute temperature.  Jean Baptiste Perrin
made such measurements in 1920.  By determining the size of single molecules,
this achievement was a compelling verification of the molecular nature of
matter for which Perrin was awarded the Nobel Prize in 1926.  Using TIRM, we
are able to measure both the mobility and diffusion coefficient for motion
normal to the wall under conditions in which that motion is severely hindered
by the wall (reduced by 10 or 100).  We show that Einstein's relationship
continues to hold even in the presence of severe wall hinderence.