Fluorimetric investigations of interactions with macromolecules in solution

Abstract

AbstractBlancophor dyes show a considerable increase in fluorescence yield upon adsorption onto poly(vinyl pyrrolidone). A fluorometric method was used for the quantitative determination of adsorption in polymer‐dye solutions. The adsorption isotherms differ from Langmuir adsorption behavior, and an adsorption isotherm is derived by taking into account the electrostatic repulsion potential of the adsorbed Blancophor ions. Adding foreign electrolytes causes a decrease in the electrostatic potential, which is independent of the species of salt, and is characterized by the Debye‐Hückel shielding parameter. The macromolecule with adsorbed ions represents a good model for a polyelectrolyte having the capability of altering or readjusting its charge density. Macromolecular sizes measured by various methods are related to the effective potential on the surface of the macromolecule. The expansion of the poly(vinyl pyrrolidone) molecule caused by the electrostatic repulsion of the adsorbed Blancophor ions was investigated by viscosity and light‐scattering measurements. Relationships among charge on the macromolecule and screening by added salt ions, on the one hand, and the molecular weight, the end‐to‐end distance, and the second virial coefficient, on the other hand were found and interpreted.