EFFECT OF CHAIN-LENGTH COMPATIBILITY ON MICELLAR STABILITY IN SODIUM DODECYL SULFATE ALKYLTRIMETHYLAMMONIUM BROMIDE SOLUTIONS/

The effect of chain length compatibility on the micellar stability was investigated for mixtures of sodium dodecyl sulfate (SDS) and alkyltr imethylammonium bromides (C(n)TAB, n = 8, 10, 12, 14, 16) at a 20/1 mo lar ratio. It was observed that the surface properties of surfactant s olutions were influenced by the chain length compatibility of the surf actant molecules. The slow micellar relaxation time (tau(2)), which di rectly correlates to the micellar stability, was determined using the pressure-jump technique. The addition of C,TAB to SDS solutions result s in a significant increase in the relaxation time compared to SDS alo ne showing a maximum for the SDS/C(12)TAB system. The high micellar st ability results in minimum surface tension, maximum surface viscosity, maximum micellar lifetime, maximum foam stability, and minimum foamab ility. The higher micellar stability as observed for SDS/C(12)TAB is a ttributed to both the chain length compatibility and the Coulombic int eraction of the surfactant head groups, resulting in an optimum packin g of molecules in micelles and at the air/water interface.