The OH-stretch absorption of liquid in CTAB micelles of various sizes, after subtraction of the solvent background. The NaBr spectrum is an absorption spectrum for a solution of NaBr in 1:500 of molality 6. The bulk spectrum is an absorption spectrum for 1:1000 .
Pump induced absorbance change plotted as a function of probe delay at at various micelle sizes. The vibrational relaxation has biexponential character. The absorbance change is defined as , where is the time-dependent transmittance after excitation by the pump and the time-independent transmittance in the absence of pump excitation.
Pump induced absorbance change plotted as a function of probe delay at , comparing CTAB (∎) and CTAC (●) micelles of . The slower component in the vibrational relaxation is associated with the surfactant counterion, which is bromide for CTAB and chloride for CTAC. Water in the first solvation shell of chloride has a faster vibrational relaxation than the solvation shell water of bromide (Ref. 33).
Spectral pump-probe amplitudes for anion-bound and bulklike OH groups as a function of probe frequency . Following the definitions in Eq. (3), the bulklike water spectrum (∎) equals and the anion-bound water spectrum (엯) equals .
Gaussian absorption line shapes for bulklike and anion-bound water, extracted from pump-probe spectra. The data are scaled relative to the sum of the spectrally integrated peak area of bulklike and anion-bound water.
Relative fraction anion-bound water (see Table II) obtained by spectrally integrating the peak areas of bulklike and anion-bound water (see Fig. 5). For comparison, the interfacial water fractions for anionic AOT micelles (Ref. 27) are shown as well.
Anisotropy decay of the OH-stretch vibration at for three sizes of CTAB reverse micelles (, 4, and 8). The mobility of anion-bound water increases when the micelle water content is increased.
Anisotropy decay curves and their fits on a linear scale for three sizes of micelles. For each graph, additional curves for and have been added for comparison, corresponding to cone angles of and 43°, respectively. For very near to 1, the anisotropy decay is slowed down at early delays, in specific cases leading even to a recovery of the anisotropy.
Directionality of the hydrogen-bond between water and sulfonate (a) and between water and bromide (b). The angle refers to the cone semiangle given in Eq. (7).
Schematic overview of the model that describes the population dynamics for both types of excited HDO molecules . Relaxation from the excited 1 state proceeds via an intermediate level . The cross section of the intermediate level is taken to be equal to that of the ground state. The cross section of the transition is assumed to be time independent.
OH-stretch vibrational and reorientational lifetimes (in ps) and parameters of bulklike and anion-bound water in CTAB reverse micelles.
Relative fractions and line shape parameters of bulklike and anion-bound water in CTAB reverse micelles.
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