Influence of a neutral polymer (PVP) on the solvatochromic properties of SDS micelles.

In the present work, we have studied the influence of a water-soluble neutral polymer (poly-N-vinyl pyrrolidin-2-one, PVP) on the Kamlet-Taft polarity parameters of sodium n-dodecyl sulfate (SDS) micelles. We have used pyrene as an independent dipolarity/polarizability (pi parameter) descriptor molecule. It has been found that the addition of polymer (0.1 wt % PVP) increases the pi value of SDS micelles, suggesting that PVP-SDS aggregates have a larger dipolarity/polarizability than that of SDS micelles. Linear solvation energy relationships involving the fluorescence transition energy of four structurally similar ketocyanine dyes have also been used to evaluate the polarity parameters. It is interesting to observe that the addition of polymer leads to a decrease in both the hydrogen-bond donation (alpha-parameter) and hydrogen-bond acceptance ability (beta-parameter) of the micellar aggregate formed by PVP-SDS, whereas the dipolarity/polarizability value shows an increasing trend. Moreover, convergent results have been obtained for the pi value for PVP-SDS aggregates, using pyrene as a pi descriptor and ketocyanine dyes as molecular probes.