We have measured the diffusion coefficients, D, of aqueous micelles formed by cetyltriethyl-, cetyltripropyl- and cetyltributyl-ammonium bromides (CTEABr, CTPABr and CTBABr, respectively) and cetyltriethyl- and cetyltripropyl-ammonium hydroxides (CTEAOH and CTPAOH, respectively) by dynamic light scattering (DLS) at several temperatures from 15 to 55 °C and a range of surfactant (0.01–0.05 M) and salt (0.02–0.06 M NaBr; 0.05–0.3 M NaOH) concentrations. From values of D, we derived the respective fractional ionization values of micellar surfaces. For surfactants with bromide counterion we obtained fits of the diffusivity data using the linear interaction/DLVO approach, thus yielding estimates of the micellar hydrodynamic radius, Rh, and the micellar fractional ionization, α, which ranged from 0.26 to 0.35. For CTEAOH and CTPAOH, the fits appeared to be poorly sensitive to changes in the London-Van der Waals interactions, as expressed by the Hamaker constant, and only a large fractional ionization could account for the observed diffusivities. Display omitted •Cetyltrialkylammonium bromide and hydroxide micelles were investigated by dynamic light scattering.•Linear inteaction-DLVO theory was adopted as a simple approach to evaluate interaction behavior of micelles.•Micelles remained essentially spherical throughout the temperature and ionic strength ranges.•Fractional ionization, α, for Br- micelles ranged from 0.26 to 0.35, with Hamaker parameters increasing with the head group bulk.•Fractional ionization for OH- micelles is much higher (0.58 to 0.65); fits are rather insensitive to the Hamaker parameter.