The scattered light intensity and the intensity‐correlation function of sodium dodecyl sulfate solutions with surfactant concentrations ranging from below the critical micellar concentration up to 50 mM were measured.
From plots of the scattered light intensity versus SDS‐concentration it followed that aggregates of long chain alcohols were absent. These were removed by a foaming procedure. Intensity‐correlation functions were measured with a digital autocorrelator (Malvern) operating in the clipping mode. Using a procedure introduced by Koppel (1972) the measured intensity correlation functions were fitted to a power series in time. In the case of a pure diffusive motion this procedure allowed the determination of the (number‐averaged) diffusion constant and to estimate the width of the size distribution of the diffusing particles.
The main results are:
There is an overall increase of the diffusion coefficient with increasing SDS‐concentration, possibly due to the interaction of micelles.
The calculation of the hydrodynamic radius of the micelles by using the Einstein relation gives a lower value than would be expected from the chain length of the SDS‐molecules. This could be attributed to the dependence of the diffusion coefficient on the charge of the micelles.
There is a dip in the diffusion constant versus SDS‐concentration plot between 20 and 25 mM. Because no abrupt change can be seen in the integrated intensity, we assume that the correlation function in that concentration region is not only affected by the diffusive motion of the micelles but also by some other dynamic processes of the system.
1992 electric properties, superconductors, semiconductors electric properties, superconductors, semiconductors D 8000
-012Room Temperature Molten Polyiodides.-Room temp. molten polyiodides are obtained from the reaction of dry I2 with iodides of large cations R+: MeEt3N+, Oc4N+ (Oc: octyl) and Et3S+ (80 • C, sealed glass-tube, 6 h). The liquid polyiodides exhibit electrical conductivities in the range 10-3 to 4·10-2 s/cm. For the R4NIx compounds (x = 3, 5, 7, 9), it is found that the electric conductivity increases with increasing polyiodide chain (i.e., with increasing x) and, therefore, it is excluded that an ionic transport mechanism is responsible for the conduction behavior. A Grotthus-like charge transfer along the polyiode chains is proposed to explain the conduction behavior of the molten iodides. -(STEGEMANN, H.; ROHDE, A.; REICHE, A.; SCHNITTKE, A.; FUELLBIER, H.; Electrochim. Acta 37 (1992) 3, 379-383; Dep. Chem., Univ. Greifswald, O-2200 Greifswald, Fed. Rep. Ger.; EN)
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