Structure and properties of fluids composed of polyelectrolyte and ionic surfactant in the organic phase: Poly(allylamine) and sodium bis(2-ethylhexyl)sulfosuccinate

The structure and properties of an oil-rich microemulsion containing the cationic polyelectrolyte poly(allylamine) hydrochloride, PAAN, were investigated. An anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate AOT, was selected. The patterns of the small-angle X-ray scattering SAXS were drastically changed from those of the polymer-free AOT microemulsions. Electric conductivity and the SAXS patterns indicated the formation of the pearl-necklace structure in the polymer-containing microemulsion. Two kinds of the characteristic size, R-1 and R-2, were evaluated from the SAXS patterns. R-1 was the droplets (pearl) size that was essentially controlled by water-to-surfactant mole ratio W-0. R-2 was the size of the polymer chain connecting the droplets. Re of the salt-free system was near the end-to-end distance of an uncharged polymer chain whose degree of polymerization was the same as that of used PAAN. PAAN behaved like an uncharged polymer due to the strong electrostatic interaction with AOT. This was supported by the dynamic light scattering experiment. R-2 was affected by the salt concentration in the aqueous solution, which was attributed to the change in the strength of the electrostatic interaction between AOT and PAAN. The AOT aggregates retained the original form even in the presence of the polymer strongly interacting with AOT.