In his classic 1905 paper on brownian motion, Einstein realized that by separately measuring mobility m and diffusion coefficient D of the same particle, one could obtain the value of Avogadro’s number from RTm/D, where R is the universal gas constant and T is temperature. In 1920 Perrin performed such experiments and obtained a good value for Avogadro’s number. This success laid to rest any remaining doubts about the molecular theory of matter. Today we write Einstein’s relation as D = mkT (k is Boltzmann’s constant) and substitute m obtained from Stokes equation. As a rigid sphere approaches a rigid wall, Brenner (1961) showed that wall hinderence causes m to approach zero. Does Einstein’s equation still hold such that D approaches zero also? In this talk I will show direct measurements of D and m obtained using Total Internal Reflection Microscopy. Both quantities are found to be a few percent of their bulk values when the gap between the spherical particle and the wall is a few percent of its radius.
Dennis C. Prieve is the Gulf Oil Foundation Professor of Chemical Engineering at Carnegie Mellon University. He also currently serves as President of the International Association of Colloid and Interface Scientists (IACIS) and Editor of Colloids and Surfaces A.
He joined CMU in 1975 after receiving a Ph.D. from the University of Delaware and a B.S. from the University of Florida in 1970. Prieve’s research interests focus on the nature and measurement of colloidal forces and their effect on transport of colloidal particles, especially electrokinetic phenomena and chemically-driven flows. Since 1987, he and his students have developed Total Internal Reflection Microscopy which uses evanescent-wave scattering and optical tweezers to measure sub-piconewton colloidal forces between a single microscopic sphere and a flat plate without touching the sphere.
Prieve has been a visiting professor at Princeton University and the University of Melbourne, Australia. He received the 2011 ACS Award in Colloid & Surface Chemistry and the 2007 Lectureship Award of the Colloid Science Division of the Japanese Chemical Society. Elected Fellow of the American Institute of Chemical Engineers in 2004, he also received the AIChE Alpha Chi Sigma Award for chemical engineering research in 1995. Prieve chaired the 2002 Gordon Research Conference on Chemistry at Interfaces and co-chaired the 2004 International Electrokinetics Conference (ELKIN)