Conductivity Measurements Across the Phase Boundary

In close vicinity to the salting out phase transition, the effective charge density was determined by conductivity measurements in combination with the known and estimated electrophoretic mobilities of the counterions and the polyions, respectively. The procedure is based on the fact that, shortly before the precipitation of the polyion, the conductivity comprises contributions of polyions, free counterions and added salt. After precipitation of the polyion by reducing the temperature the conductivity is given solely by the supernatant aqueous salt solution, thus the difference Act is due to polyions and free counterions 

For most samples investigated, the temperature interval during which precipitation occurs, is quite small, i.e. 2-5 °C, as shown in Fig. 10. The upper dotted curve in Fig. 10 represents the temperature dependence which would be expected for the polyion solution if no precipitation occurs and if the fraction of free counterions would not increase with temperature, i.e. the increase in conductivity is solely caused by the decrease of the viscosity of water. Act may be utilized to determine the effective charge density f by the equation 

The present samples salt out in Nal solutions, only. For I the mobility is Hi= 8 10-4 cm2V 1 s 1. The polyion mobilities were measured by electrophoretic light scattering, shown in Fig. 11. Although at low salt np linearizes 

Despite the strong scatter of the data there is a tendency of fa to decrease with increasing cs as graphically shown in Fig. 14. 

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