The interaction of two polyamines, hyperbranched polyethyleneimine (PEI) and linear poly(vinylamine)
(PVAm), with the anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution was studied at high
pH by conductometry and potentiometry. At high pH, these polymers are protonated to only a very small
degree. As very weak polyelectrolytes, they should behave in a manner similar to that for nonionic polymers.
Upon titration of the PEI and PVAm aqueous solutions with SDS, the conductivity increases over the whole
range of SDS concentrations. The character of the conductivity changes, however, is different from that
of typical nonionic polymers, such as poly(ethylene oxide) or poly(vinylpyrrolidone). Unlike these nonionic
polymer−surfactant systems, the absolute values of the specific conductivity of aqueous SDS solutions in
the presence of PEI and PVAm are higher than that for pure SDS over the whole range of SDS concentrations.
Potentiometric measurements showed that binding of SDS to PEI and PVAm is accompanied by the
consumption of protons and, as a consequence, by an increase in the pH of the solutions. It has been shown
that the contribution of OH- ions to the increase in the conductivity of PEI−SDS and PVAm−SDS systems
should be taken into account. Some other possible mechanisms of the unusual behavior of the conductivity
versus [SDS] plots in the presence of PEI and PVAm have been also proposed.
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.
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