Controlling the aggregation of sodium dodecylsulphate in aqueous poly(ethylene glycol) solutions

Abstract

The interaction between polymers and surfactants has been a topic of study due to their various applications, though for this purpose, a better understanding of these interactions and the ability to control them is also important. In the present work, we explore the interaction of a well known polymer, poly(ethylene glycol) (PEG) of different molecular weights (400, 6000, 10 000 and 20 000 g mol⁻¹) and an anionic surfactant sodium dodecylsulphate (SDS), by using the techniques of surface tension, conductance and small angle neutron measurements. The surface tension isotherms indicate the presence of two breaks in the case of high molecular weight PEG's. At the first break point a surface tension minimum occurs which has been attributed to the onset of PEG–SDS interaction leading to the formation of SDS aggregates on the PEG chains. The second break point is due to the formation of free SDS micelles. These observations have been well supported by conductance and small angle neutron scattering (SANS) measurements. SANS indicates the formation of a bead-necklace structure of micelle-like clusters of the surfactant formed along the unfolded polymer chain in the case of PEG-20 000. The role of added NaCl in these interactions and its ability to control the aggregation of SDS has also been addressed in the present work, thus throwing light on the importance of electrostatic interactions in polymer–surfactant interactions.