Influence of hydrophobically modified polyelectrolytes on CTAB-based w/o microemulsions

This paper is focused on the influence of anionic polyelectrolytes on the inverse micellar region (L2 phase) of the quaternary system cetyltrimethylammonium bromide/toluene–pentanol (1:1)/water. The properties of the different macromolecules have been changed by the gradual incorporation of hydrophobic side chains. Thus, commercially available poly(acrylic acid) has been hydrophobically modified by grafting with butylamine.With increasing hydrophobicity of the PAA, the charged polymers induce a clear diminution of the water solubilization capacity of the microemulsion at a given polymer concentration of 1%. The isotropic polyelectrolyte-modified L2 phase has been also investigated in much more detail by means of conductometric, rheological and calorimetric measurements. The polyelectrolyte-modified microemulsion shows a typical low shear viscosity and Newtonian flow behaviour. The conductivity measurements indicate the characteristic features of percolated microemulsion droplets.An increase of the hydrophobicity leads to a decrease of the acidity of the carboxy groups, as to be demonstrated by potentiometric measurements. However, titration experiments with a surfactant selective electrode show that the cooperativity of the interactions between the hydrophobic-modified polyelectrolyte and the surfactant molecules is decreased due to the formation of microdomains. Basing on this knowledge, the decrease of the area of the L2 phase with increasing hydrophobicity of the PAA becomes plausible due to the precipitation of more hydrophobic polyelectrolyte-surfactant complexes.