Comparison of the association level of a pyrene-labeled associative polymer obtained from an analysis based on two different models.

A hydrophobically modified alkali swellable emulsion copolymer (HASE) was labeled with pyrene and its fluorescence behavior was monitored by steady-state and time-resolved fluorescence as increasing amounts of the surfactant sodium dodecyl sulfate (SDS) were added to the solution. In aqueous solution, the pyrene pendants are aggregated. As SDS is added, the surfactant binds to the pyrene aggregates, which leads to their breakup at an onset SDS concentration of 1.25 x 10(-3) mol/L. The breakup of the pyrene aggregates is complete at 4.25 x 10(-3) mol/L, which is slightly larger than the critical micellar concentration of SDS in 0.01 M Na(2)CO(3) aqueous solution at pH 9 found to equal 3.5 x 10(-3) mol/L by surface tension measurements. The pyrene pendants were present as different species in solution, and the fractions representative of all emissive pyrene species were determined from the global analysis of the monomer and excimer fluorescence decays. Two analyses were applied to the decays. In the first analysis, the diffusional encounters between pyrene pendants were described by the blob model. In the second analysis, no assumptions were made on how the pyrene pendants encountered each other. Both analyses yielded identical results which demonstrate that the determination of the fractions of the different emissive pyrene species of a solution of a pyrene-labeled associative polymer does not depend on the model chosen to account for the diffusional encounters taking place between pyrene pendants.