Interaction of Pyrene-Labeled Poly(ethylene imine) with Sodium Dodecyl Sulfate in Aqueous Solution

The interaction between pyrene-labeled poly(ethylene imine) (PEI−Py), a hyperbranched polymer, and the anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution was studied using steady-state fluorescence measurements. Fluorescence experiments were carried out with PEI−Py containing approximately one Py group per 900 monomer polymer units (PEI−Py/900) at two different pH and at two polymer concentrations. When SDS was added to the PEI−Py/900, at both pH 6.6 and pH 10, the monomer fluorescence I M increased significantly, with a much less pronounced change in the excimer emission ( I E ). In the absence of SDS, the monomer intensity is substantially reduced due to quenching of Py* by secondary and tertiary amino groups of the polymer, whereas the excimer emission is less affected. The increase in I M with increasing SDS concentration indicates that SDS molecules protect Py* from quenching, through formation of polymer-bound micelles formed at the sites of the Py groups. In contrast, I E remains practically unchanged (0.3 wt % PEI, pH 6.6) or decreases. The decrease in I E is attributed to disruption of Py aggregates upon their binding to SDS.