GROWTH OF GIANT RODLIKE MICELLES OF IONIC SURFACTANT IN THE PRESENCE OF AL3+ COUNTERIONS

To interpret quantitatively experimental data for the growth of rodlik e anionic surfactant micelles in the presence of Al3+ ions, we underto ok experimental and theoretical investigations. We determined the mice lle size, shape, and interactions by light scattering and examined the binding of Al3+ ions to the micelles by ultrafiltration. Independent static and dynamic light scattering measurements indicated that the ef fect of the micelle-micelle interactions in these solutions can be neg lected. The major factor promoting the micelle growth turns out to be the binding of Al3+ ions to the micelle surfaces, which considerably a ffects the standard chemical potential of the aggregated surfactant mo lecules and can alter the micellization constant by orders of magnitud e. The latter effect was described theoretically. The model of micelle growth, extended in this way, compared well with the experimental dat a. The model provides a quantitative description of the micelle size a nd charge as functions of the surfactant and electrolyte concentration s. It turns out that the rodlike micelles have a lower surface charge than the spherical ones, and this makes their growth energetically fav orable. A practical application may follow from the markedly greater s olubilization efficiency of the studied rodlike micelles compared to t he spherical ones.