Adsorption of Sodium Diisooctyl Sulfosuccinate onto Calcium Oxalate Crystals.


L Tunik, H Fueredi-Milhofer, and N Garti. 1998. “Adsorption of Sodium Diisooctyl Sulfosuccinate onto Calcium Oxalate Crystals.” Langmuir, 14, 12, Pp. 3351–3355.


The adsorption of diisooctyl sulfosuccinate (AOT) from high ionic strength soln. onto well-defined calcium oxalate monohydrate (COM) and dihydrate (COD) crystals was studied. Adsorption at the COM/soln. interface is characterized by a two-step (LS type) isotherm, starting at low equil. concns. (5 mg dm-3). At ceq = 15-30 mg dm-3 it reaches a plateau which is followed by a relatively steep inflection (ceq = 30-50 mg dm-3) and a further slow increase of the adsorption as a function of increasing AOT concn. In suspensions without surfactant the particles were neg. charged. Upon adsorption an initial slight decrease of the neg. $\zeta$-potential, coinciding with the first plateau, occurred which was followed by a sharp increase in concordance with the increasing surface concn. of the surfactant. In contrast, adsorption onto COD is characterized by a sigmoid isotherm. It commenced at 14 mg dm-3 of AOT and increased abruptly up to a plateau. The max. adsorbed amt. was about half the max. amt. adsorbed on COM, the corresponding adsorption densities in mols. per square nanometer being 7.45 for COD and 14.22 for COM, resp. COD crystals suspended in electrolyte soln. without surfactant were almost uncharged, and the neg. $\zeta$-potential increased in concordance with AOT adsorption. The results are discussed in accordance with literature data and by considering the ionic structure of the different crystal faces. It is assumed that the first adsorption step in the COM/surfactant system is due to electrostatic interactions causing head-on adsorption of the surfactant mols. at high-energy sites, while in the second step a bilayer is formed. In the COD/surfactant system the hydration layers covering the COD crystal faces are shielding them from electrostatic interactions. Consequently AOT adsorption at the COD/soln. interface proceeds only through surface aggregation, resulting in a bilayer of intertwined surfactant mols. [on SciFinder(R)]
Last updated on 05/27/2020