EFFECT OF COUNTERION ON THE SIZE AND CHARGE OF ALKYLTRIMETHYLAMMONIUM HALIDE MICELLES AS A FUNCTION OF CHAIN-LENGTH AND CONCENTRATION AS DETERMINED BY SMALL-ANGLE NEUTRON-SCATTERING

The influence of counterion on micelle structure is examined for a series of trimethylammonium halide surfactants C(n)TAX = CnH2n+1 N(CH3)3+X- (X = NO3, Br, CH3SO4, Cl, and OH) by small-angle neutron scattering. The variation of micelle structure as a function of chain length (n = 12, 14, and 16) and surfactant concentration (0.05, 0.1, and 0.2 mol dm-3) is also studied. It was found that the aggregation number, N, increases in the order of NO3 > Br > CH3SO4 > Cl much greater than OH. This order is roughly correlated to the fractional micellar charge, beta, which follows the order OH > Cl > CH3SO4 approximately Br approximately NO3. Fractional charge changes very little and in an irregular fashion when n and/or surfactant concentration are in but the aggregation number increases with respect to both.