Properties of the lignosulfonate-surfactant complex phase

The association of lignosulfonate (LS) and cationic surfactant (S) has previously been shown to be cooperative, giving a complex, concentrated gel phase (LS/S) at concentration ratios near charge equilibrium between LS and S. In the present work, we have studied the effect of seven variables on the partitioning of LS/S from aqueous- to oil phase. The molecular weight of LS, pH, and the concentration ratios of ionic groups were found to be decisive for the partitioning. A detailed study of the seven variables in terms of polar and dispersive contributions to the surface free energy of the LS/S has been attempted, using contact angle measurements. The method failed to yield quantitatively significant results because of large experimental errors. LS/S has been dispersed in oil-phase by means of oil soluble surfactants. The stability and aggregate size distribution have been studied by photosedimentation. The nature and concentration of the surfactant was found to be of importance, suggesting adsorption to LS/S through hydrophobic interactions. (C) 2001 Elsevier Science B.V. All rights reserved.