Ultracentrifuge as a Versatile Tool to Study Preferential Interaction of Polymers in Mixed Solvents

Abstract

Over the past five decades the analytical ultracentrifuge has been a versatile tool in the study of macromolecules and colloidal particles. Several textbooks [1–4] and review articles [5–10] deal with experimental techniques and theories for complete characterization of macromolecular species. However, the first published articles on the analytical ultracentrifuge dealt with the analysis of particle size distributions in suspensions of inorganic colloids. The emphasis has now shifted to organic polymers following the discovery that a large number of such polymers exist in nature. Before the development of the ultracentrifuge, the existence of such giant molecules was not recognized; the molecular kinetic units of proteins and of high organic polymers in solution were simply thought of as clusters of much smaller molecules, forming particles of undefined mass. Beginning with the elegant investigations of Svedberg [11, 12] on ultracentrifugation, such substances were revealed to be macromolecules, large because they contain a huge number of atoms connected together by primary chemical bonds [13]. Following a long and fruitful series of investigations in the early twenties and thirties, Svedberg wrote in one of his articles [12], “the proteins are built up of particles possessing the hallmark of individuality and therefore are in reality giant molecules. We have reason to believe that the particles in the protein solutions and the protein crystals are built up according to a plan which makes every atom in them indispensable for the completion of the structure.” Almost at the same time, it was Staudinger [14] who clearly demonstrated that substances such as polystyrene and natural rubber exist in solution without change in molecular weight regardless of the solvent employed .