Time-resolved fluorescence and small angle neutron scattering study in pluronics-surfactant supramolecular assemblies.

Interaction of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), with pluronics F88 (EO(103)-PO(39)-EO(103)) and P105 (EO(37)-PO(56)-EO(37)) micelles and its effect on modulating the location of an anionic solute in the mixed micelles have been investigated using time-resolved fluorescence and small angle neutron scattering (SANS) studies. SANS results indicate the formation of pluronic-CTAB supramolecular assemblies, in which the hydrophobic chains of CTAB occupy the hydrophobic core of the pluronic micelle while the positively charged head groups reside at the micellar core-corona interface. Rotational correlation time of the anionic probe in these supramolecular assemblies increases with an increase in the CTAB concentration, and the observed results are explained on the basis of the probe movement from the surface to the interior of the micelle due to the increased electrostatic attraction. Dynamic Stokes' shift measurements also support the movement of the probe due to the addition of the surfactant to the supramolecular assemblies. From the studies with different pluronics, it is indicated that the concentration of CTAB required to drag the probe molecule into the interior of the micelles is linearly correlated to the thickness of the corona region of the respective micelles.