engleski

Counterion Binding to Ionic Micelles: Effects of Counterion Specifity

The effects of counterion specifity on the properties of sodium dodecyl sulfate micelles containing photochemically reactive solubilizates were studied by laser flash photolysis and light scattering, potentiometric, spectroscopic and microelectrophoretic measurements. The counterions investigated were an amphiphilic ion (cetyltrimethylammonium, CTA+) and two divalent ions (cupric, Cu2+, and methylviologen, MV2+). Cu2+ and MV2+ showed lower effect than CTA+ in promoting changes of micelle size and electrostatic potential at the micelle/solution interface. This can be attributed to the complex interplay between electrostatic and hydrophobic interactions, which determine the average location of counterions, i.e., prevailing interfacial or intercalated binding to the micelle. Laser flash photolysis showed that Cu2+ enhanced the rate of decay of biphenyl triplet, while MV2+ did not show any effect. The differences between the quenching cations were attributed to the average location of MV2+ ions in the Stern layer further away from the micelle core than Cu2+.

counterion binding; micelles; surfactants

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