Dynamics of adsorption of polyallylamine hydrochloride/sodium dodecyl sulphate at water/air and water/hexane interfaces

The present work is devoted to the study of interactions between a cationic polyelectrolyte and an anionic surfactant in the solution bulk and at the water/air and water/oil interfaces. For this purpose surface and interfacial tensions, zeta potential, ellipsometry and dynamic light scattering (DLS) were used to describe the formation of complexes of polyallylamine hydrochloride (PAH) and sodium dodecyl sulphate (SDS). Surface and interfacial tension results are supported by zeta potential measurements and aggregation size measurements via DLS. Due to electrostatic binding of dodecyl sulphate anions to the positive charges of the polyelectrolyte chains the resulting complexes become more hydrophobic. At the 1:1 ratio of PAH:SDS the complexes precipitate and become recharged due to the additional hydrophobic binding of SDS ions. The complexation leads to a depletion of surfactant and hence to an increase in surface and interfacial tensions.

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► PAH-SDS complex in the bulk, at the water/air and water/oil interfaces studied.
► Complex becomes more hydrophobic due to electrostatic binding.
► PAH-SDS complex precipitates and becomes recharged at the 1:1 ratio.
► Complexation leads to a depletion of surfactant and to an increase in surface and interfacial tensions.