Statistical distributions and collision rates of additive molecules in compartmentalized liquids studied by EPR spectroscopy. 1. Sodium dodecyl sulfate micelles, 5-doxylstearic acid ester, and cobalt(II)

Abstract

A technique to study the statistical distribution and collision rates of additive molecules in compartmentalized liquids is developed and applied to C O ( H~O )~~+ in SDS micelles. The physical model employs a dilute solution of a nitroxide free radical, the indicator, in the presence and absence of a varying concentration of paramagnetic molecules, the broadeners, which are C O ( H~O )~~+ in this case. The EPR spectra of the indicator vary nonlinearly with the concentration of the broadener in a manner consistent with a hypothesis that the resident time of a CO(H~O)~*+ ion on one micelle is long compared with lO-'s but inconsistent with a random distribution of the added divalent cations among the micelles. A simple theory is developed which takes into account interactions between broadeners residing in the same compartment and ignores such interactions if they reside in different compartments. Assuming a small electrostatic repulsion between the cations brings the experimental results into agreement with theory and allows the collision rate of the broadener with the indicator to be estimated. For C O ( H~O )~~+ ,this collision rate decreases linearly as a function of the inverse volume of the micelle as predicted by a simple random walk model. The polarity of SDS micelles, as estimated by the I4N hyperfine coupling constant of the indicator, decreases linearly with micelle size, while the microviscosity, as estimated from the rotational correlation time of the indicator, increases linearly with this size.

Effect of terbium(III) chloride on the micellization properties of sodium decyl- and dodecyl-sulfate solutions

“…5), the addition of terbium(III) chloride to SDS solutions results in a continuously increasing scattering intensity between 0 and 10 mM SDS, which corresponds to the beginning of SDS-micelle formation, according to conductivity data (cac ap = 9.63 mM to [Tb(III)] = 0.53 mM). This seems reasonable, since it is known from both luminescence quenching studies [30], and EPR spin probe measurements [31], that micelle size is greater in the presence of higher valence ions than in pure SDS. This behaviour also occurs for SDeS-TbCl 3 solutions.…”

Organization of amphiphiles

“…7). The polarity of the SDS micelle, as estimated by the 14 N hyperfine coupling constants of the indicator, is also reported to decrease along with an increase in the micelle size [60].…”

“…The positive value of the interaction parameter (2.76) suggests bluntly that the interaction between CTAB and OP-30 is antagonistic in nature [60] and hence formation of CTAB micelles is not assisted by the OP-30 surfactants.…”

Quantifying the micellar structure formed from hydrocarbon-fluorocarbon surfactants

“…The SANS measurements were performed as detailed previously [12] on the fixedgeometry, time-of-flight LOQ diffractometer (ISIS Spallation Neutron Source, Oxfordshire, UK). All measurements were carried out at 25 o C. Experimental measuring times were between 40 and 80 minutes.…”

“…Rotational correlation times are computed from the overall linewidth of the centre line and the peak-to-peak heights of the three lines and corrected for inhomogeneous broadening using the procedure outlined by Bales [12,14].…”