Abstract: Interaction in binary systems of anionic surfactants and water-soluble nonionic macromolecules was studied by means of steady-state fluorescence quenching. The above binary systems were composed of sodium dodecyl sulfate(SDS) or sodium dodecane sulfonate(AS) with polyethyleneglycol(PEG) or polyvinylpyrrolidone(PVP). The occurrence of aggregates in the above systems was deduced from the detected pseudo-micelle aggregation number N_p. It was discovered that N_p is simply increased linear with increasing surfactant concentration c. [N_p]₁ is defind as the first critical aggregation number of the pseudo-micelle corresponding to c₁ in γ-lgc curves. The experimental results show that [N_p]₁ for a certain type of macromolecule is eventually not changed with the change of molecular weight and concentration of macromolecule. Thus [N_p]₁ seems to be an invariant or a structural eigenvalue which depends solely on the molecular structure of both surfactant and macromolecule.

Key words: Critical aggregation number of pseudo-micelle, Steady-state fluorescence quenching, Surfactant, Macromolecule