Interaction of Polymer and Surfactant at the Air−Water Interface: Poly(2-(dimethylamino)ethyl methacrylate) and Sodium Dodecyl Sulfate

• Published in: Langmuir Vol. 24; no. 22; pp. 12892 - 12898
• Main Authors: Moglianetti, Mauro, Li, Peixun, Malet, Fred L. G, Armes, Steven P, Thomas, Robert K, Titmuss, Simon
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 18.11.2008
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Interfaces: Adsorption, Reactions, Films, Forces; Surface physical chemistry; Gas liquid interface; Monolayer; Multilayer; Neutrons; Polymer; Air water interface; Surfactant; Ionic surfactant; Complexes; Lauryl sulfate; Polyelectrolyte; Anionic surfactant; Adsorption; Sodium sulfate; Distribution; pH; Surface tension; Monomer; Structure; Surface activity; Physicochemical properties; Conformation; Reflectance
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la8020468

The interactions between the weak polyelectrolyte, poly(2-(dimethylamino) ethyl methacrylate) or PDMAEMA, and the anionic surfactant sodium dodecyl sulfate (SDS) at the air−water interface have been investigated at pH = 3 and 9 using a combination of neutron reflectivity and surface tension measurements. By using deuterated PDMAEMA in combination with h-SDS and d-SDS, we have been able to directly determine the distribution of both the polymer and the surfactant at the air−water interface. At pH = 3, the polyelectrolyte is positively charged while at pH = 9 it is essentially uncharged. The enhancement in the adsorption of SDS at low coverage suggests that surface active polymer surfactant complexes are forming and adsorbing at the interface. This leads to close to monolayer adsorption of SDS, suggesting that it is surfactant monomers that are complexing with polymers that are in extended conformations parallel to the surface. As the concentration of SDS in the mixtures changes so does the surfactant content of the complexes, which affects the surface activity and hence the coverage of the complexes. Multilayer structures are formed at SDS concentrations of 0.1 and 1 mM, for pH = 3 and 9, respectively.