From Colloidal Aggregates to Layered Nanosized Structures in Polymer−Surfactant Systems. 1. Basic Phenomena

In this work, we examine the rich crystallization behavior that occurs in PbII/S-II/poly(ethylene oxide) (PEO)/sodium dodecyl sulfate (SDS) systems, in which the anionic surfactant interacts strongly with the polymer molecules, forming micellar aggregates attached to the polymer chains above the critical association concentration. Lead sulfide crystallites are formed in the vicinity of polymer-bound micelles by adding lead and sulfide ions to the polymer−surfactant solution. Surfactant-stabilized inorganic particles adsorbed on the polymer chains combine through a polymer-mediated bridging flocculation mechanism to produce characteristic rodlike colloidal aggregates. Under certain conditions, these evolve into a range of metastable structures, composed of lead sulfide, PbS, and lead dodecyl sulfate, Pb(DS)2. XRD analysis of the metastable reaction products allows us to follow the slow kinetics of their formation and reveals a well-defined layered structure, based on lead dodecyl sulfate, the thickness of ...