Thermodiffusion in Macromolecular Solutions

Abstract

As it is well known, self-beating spectroscopy has largely superceded classical techniques such as free diffusion for the determination of the diffusion coefficient of macromolecules in solution. Indeed with classical techniques one obtains the value for the diffusion coefficient from the time evolution of concentration gradients associated with a non stationary mass flow generated under precise geometrical boundary conditions¹. In a free diffusion experiment for example one prepares the sample in such a way that a sharp discontinuity in the concentration is initially built across a horizontal plane (the so called “meniscus”). A mass flow then occurs spontaneously across the boundary and persists until the concentration becomes homogeneous throughout the entire volume. Sharp menisci difficult to prepare however and the evolution of the concentration gradient can be easily upset by even the slightest amount of convective motion.