| Abstract
| - We report the use of the nonlinear optical technique of hyper-Rayleigh scattering to investigate the interactionof the cationic probe molecule crystal violet with micelles of sodium dodecyl sulfate. An absolute value of(847 ± 80) × 10-30 esu is measured at the fundamental wavelength of 870 nm for the molecularhyperpolarizability of crystal violet free in pure aqueous solutions. In aqueous solutions of sodium dodecylsulfate, above and below the critical micelle concentration, the measured hyperpolarizability of crystal violetis weaker than in the solution free of sodium dodecyl sulfate. From the comparison with linear opticalphotoabsorption spectroscopy data, this difference is attributed to electrostatic interactions between the cationiccrystal violet molecules and the negatively charged sodium dodecyl sulfate surfactant molecules present inexcess. Polarization resolved hyper-Rayleigh scattering measurements are then performed to show that, belowand above the critical micelle concentration, crystal violet molecules also undergo symmetry changes uponinteraction with sodium dodecyl sulfate. Above the critical micelle concentration, the minimum fraction ofmicelles interacting with at least one CV molecule is estimated. For instance, for a crystal violet aqueousconcentration of 150 μM, this fraction is larger than 7%.
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