Critical density fluctuations within a single polymer chain

Abstract

The coil–globule phase transition is a reversible, conformational change of a macromolecule where the high temperature (or good solvent) phase is an extended coil and the low temperature (or poor solvent) phase is a tightly packed globule¹. We now present direct observations, made by photon-correlation spectroscopy, of the sharp increase in amplitude and relaxation time of density fluctuations within a single polymer molecule as it passes through the coil–globule phase transition. This growth of fluctuations is characteristic of critical phenomena associated with phase transitions, a subject that has generated much interest over the past decade, and has been studied in a wide variety of physical systems. These are the first measurements of critical behaviour that we know of made on a three-dimensional system that can be characterized as finite in the terms of statistical mechanics.